Parental Care in Fishes – Different Methods with Examples

• Parental care in fishes refers to the behavior exhibited by adult fish to ensure the survival and development of their eggs or young ones. While not all fish species provide parental care, it is observed in many species as a means to increase the chances of offspring survival. Parental care can involve one or both sexes of the fish and can take various forms.
• In the realm of fish reproduction, approximately 77 percent of fish species show no parental care behavior. These species typically produce a large number of eggs and sperm and rely on external factors for the survival of their offspring. About 17 percent of fish species engage in caring for their eggs only, while less than 6 percent of fish species provide care for both eggs and newly hatched young.
• Parental care in fish exhibits a wide range of behaviors. Some fish species practice random spawning, where eggs are released without any further care. Others deposit a large number of eggs in various locations without offering any care. On the other end of the spectrum, certain fish species provide extensive protection and care to their offspring, ensuring their survival.
• There are two general types of parental care variations observed among fishes. The first variation involves either one or both parents engaging in caring for the offspring. This results in paternal care, maternal care, or biparental care, depending on the involvement of the parents. The second variation pertains to the location where the eggs and newly hatched young are maintained. Some species are substrate-brooders or guarders, where the eggs are kept on the substrate such as plants, under stones, or in excavated pits. In contrast, mouth brooders or incubators carry their eggs and young ones in their mouths for protection.
• Fishes have evolved various mechanisms to provide care to their fertilized eggs and young ones. These can include guarding the eggs against predators, fanning the eggs to increase oxygen supply, cleaning the eggs, and providing shelter or food resources. Parental care in fishes is a significant behavior that contributes to the survival and success of their offspring, ensuring the continuation of their species.
• It is important to note that parental care behavior may vary among fish species, and the specific strategies employed depend on the ecological niche, environmental conditions, and evolutionary adaptations of each species.

Different Types Of Parental Care In Fishes Include

1. Scattering eggs over aquatic plants
2. Depositing eggs in sticky covering
3. Laying of eggs at suitable places
4. Nest building
5. Coiling round the eggs
6. Egg brooding in mouth and intestine
7. Brood pouches
8. By the formation of egg capsules
9. Attachment of eggs to the body
10. Viviparity

1. Deposition of Eggs Into Self-Made Nest

Certain fish species exhibit the behavior of preparing nests to ensure the safe deposition and protection of their eggs, as well as the development of their young ones. The construction of these nests involves the participation of either males or both sexes, depending on the species. These nests are created using a variety of materials, including pebbles, aquatic vegetation, and secretions from their own bodies.

The purpose of nest-building is to provide a suitable environment for egg fertilization, incubation, and the subsequent growth of the offspring. Different species employ various strategies and materials to construct their nests, showcasing their unique adaptations to the aquatic environment.

Males of certain fish species take the responsibility of nest-building. They meticulously gather materials such as pebbles, small rocks, or pieces of aquatic vegetation to create a nest structure. These materials are arranged in a specific manner to form a nest that can provide protection and security to the eggs and young ones. The male invests considerable time and effort in nest construction, ensuring that it meets the requirements for successful reproduction.

In some species, both males and females participate in nest-building activities. They work together to gather suitable materials and construct a nest that fulfills the needs of the developing eggs and young. This cooperative behavior enhances the chances of successful reproduction and enhances the survival rate of the offspring.

In addition to natural materials like pebbles and vegetation, some fish species utilize secretions from their bodies to reinforce the nest structure. These secretions may come from specialized glands or mucus-producing cells, which help bind the nest materials together, making it more stable and secure.

The process of nest-building in fish is a fascinating example of parental care and adaptation to the aquatic environment. By constructing nests, these fish create a favorable microhabitat for their eggs and young ones. The nests provide protection against predators, maintain appropriate water flow and oxygen levels, and offer a suitable substrate for egg attachment and development.

Overall, the deposition of eggs into self-made nests demonstrates the remarkable behaviors and adaptations of fish species to ensure the survival and successful reproduction of their offspring. By investing time and effort in nest-building, these fish increase the likelihood of their eggs hatching and their young reaching maturity in a safe and supportive environment.

The different types of nests built are;

(a) Basin-like nests

Basin-like nests are structures created by certain fish species for the deposition and protection of their eggs. Here are some examples of basin-like nests and their characteristics:

1. Carps: Carps lay their eggs with a special sticky covering that allows them to adhere to each other or to various substrates such as stones or aquatic vegetation. This adhesive coating helps keep the eggs in place and prevents them from drifting away.
2. Yellow perch (Perca flavescens): Yellow perch deposit their eggs in a rope-like structure, where the eggs are held together by a long floating membrane. This arrangement helps keep the eggs clustered and provides some protection during incubation.
3. Angler fish (Lophius): Angler fish lay their eggs invested by a gelatinous external coat, which remains together and forms a transparent mass of considerable size. This gelatinous coating provides buoyancy to the eggs and protects them from external factors.
4. Flying fishes, skippers, garfishes, etc.: Some fish species, such as flying fishes, skippers, and garfishes, secrete a sticky thread-like substance from their kidney. The eggs are attached to this sticky thread, with one end adhered to an aquatic substrate and the other end remaining free. This arrangement helps anchor the eggs while allowing some mobility.

These examples illustrate the various strategies employed by fish species to create basin-like nests or structures that aid in the protection and development of their eggs. The sticky coatings, floating membranes, gelatinous coatings, or thread-like substances play crucial roles in keeping the eggs together, preventing them from dispersing, and providing some degree of protection. These adaptations ensure the survival and successful incubation of the eggs, enhancing the reproductive success of these fish species.

(b) Circular nest

A circular nest is a type of nest structure created by certain fish species for the purpose of egg deposition and protection. Here are a couple of examples of fish species that construct circular nests:

1. Male Bowfin (Amia calva): The male Bowfin prepares a crude pit-like circular nest among aquatic vegetation. The male then invites a female to spawn in the nest, where she deposits her eggs. The male fertilizes the eggs, and thereafter, he assumes the responsibility of protecting the nest until the young ones hatch. Once the young ones have hatched, they are allowed to leave the nest under the protection of the father. This circular nest provides a safe environment for the eggs and young ones, ensuring their survival and development.
2. Some catfish species (Arius): In certain catfish species found in North America, both the male and the female participate in preparing a crude circular nest in the mud at the riverbed. The nest typically has a diameter of about 50 cm and may be supplemented with a protective cover of logs or stones. After the eggs are laid and fertilized, both parents do not provide any further care or protection for the eggs. The eggs are left uncared for and rely on natural conditions for their development.

These examples demonstrate the diverse strategies employed by fish species in constructing circular nests for their eggs. The nests provide a centralized location for egg deposition and offer some degree of protection, ensuring the survival of the offspring. While some fish species exhibit parental care and guard the nest until the young ones hatch, others rely on the natural environment for the development of their eggs. The construction of circular nests is an adaptive behavior that enhances the reproductive success and survival of these fish species.

(c) Hole/Burrow nest

A hole/burrow nest is a type of nest structure created by certain fish species, where they excavate holes or burrows in their habitat for the purpose of egg deposition and protection. Here are a couple of examples of fish species that construct hole/burrow nests:

1. African lungfish (Protopterus): The male African lungfish prepares a simple nest in the form of a deep hole in swampy areas along the river bank. The nest is surrounded by long aquatic weeds and grasses. After spawning, the male lungfish keeps guard over the nest, occasionally aerating the water by his slow body movement. This aeration helps in maintaining oxygen levels for the developing eggs.
2. South American lungfish (Lepidosiren): The South American lungfish constructs a nest in the form of a burrow in swampy areas. The burrow can vary in length from 1 to 2 meters and consists of a short vertical portion and a larger horizontal portion where the eggs are deposited. In this species, the males take care of the eggs. During this period, they develop a long red filament from their pelvic fins. This filament performs the function of aeration, allowing oxygen to reach the eggs without the male lungfish having to come to the surface to gulp air.

These examples highlight the nesting behaviors of lungfish species, where they create holes or burrows in their habitat to provide a safe environment for their eggs. The males assume the responsibility of guarding the nest and ensuring the well-being of the developing eggs. The construction of hole/burrow nests allows these fish species to protect their eggs from potential predators and maintain suitable conditions for successful reproduction.

(d) Barrel-shaped nest

• A barrel-shaped nest is a specific type of nest constructed by certain fish species, characterized by its compact and tunnel-like structure resembling a barrel. Here’s an example of a fish species that builds a barrel-shaped nest:
• Male sticklebacks (such as the three-spined stickleback, Gasterosteus aculeatus, and the ten-spined stickleback, Pygosteus pungitius) construct elaborate nests before the start of courtship. The male stickleback first selects a suitable location in shallow water where the flow is continuous but not too swift.
• Using a combination of plant fragments, rootlets, and weeds, the male stickleback builds the nest by binding these materials together with a sticky secretion from its kidney. The male engages in various activities such as probing, boring, sucking, and gluing to create a compact nest with a tunnel-like structure capable of receiving the eggs (resembling a barrel).
• Once the nest is ready, the male stickleback sets out in search of a mate. When encountering a female with a bulging abdomen, signaling her readiness to lay eggs, the male performs a zigzag dance around her, displaying his red spot. If the female is receptive, she responds by curving her head and tail upwards. Together, they swim to the nest, and the male opens the entrance of the nest with his snout.
• The female then deposits two to three eggs inside the nest and swims out through the opposite side of the entrance. The male promptly enters the nest and fertilizes the eggs. He repeats this process with other females until a sufficient number of eggs are laid. The male takes on the role of guarding the nest and ensures proper aeration by fanning the eggs with his fins and tail. As the eggs develop, the male maintains a close watch over the brood, preventing any young ones from straying away.
• The construction of a barrel-shaped nest in stickleback fish species is a fascinating reproductive behavior that provides a safe and suitable environment for the eggs. The male’s active involvement in nest building, mate selection, egg fertilization, and parental care contributes to the successful reproduction and survival of their offspring.

(e) Cup-shaped nest

• A cup-shaped nest is a specific type of nest constructed by certain fish species, characterized by its concave shape resembling a cup. Here’s an example of a fish species that builds a cup-shaped nest:
• The male Apelts quadracus, a fish species, constructs an elaborate cup-shaped nest that is attached to rooted plants near the bottom of the water. The construction of this nest involves a unique process.
• When a female lays a clutch of eggs, the male starts building an extension of the nest. This extension is built up and over the eggs, forming a concave upper surface within the nest. The purpose of this extension is to create additional space for future clutches of eggs.
• After the extension is built, a second female lays another clutch of eggs on the new concave floor created by the extension. This process can be repeated multiple times, with each female laying her clutch of eggs on the concave surface of the previous extension. As a result, the male ends up with several clutches of eggs stacked vertically within a multi-tiered nest, each clutch occupying its own concave section.
• By constructing a cup-shaped nest with multiple tiers, the male Apelts quadracus maximizes the use of available space and provides separate compartments for each clutch of eggs. This nesting strategy allows for efficient egg deposition and provides a safe and organized environment for the developing embryos.
• The construction of a cup-shaped nest in Apelts quadracus showcases the complexity and ingenuity of fish reproductive behaviors. The male’s effort in building and maintaining the nest demonstrates his dedication to ensuring the successful incubation and survival of the eggs.

(f) Floating nest

• Certain fish species, such as the male Mormyrids (specifically Gymnarchus), construct unique nests known as floating nests. These nests are created with the assistance of aquatic vegetation and have distinctive characteristics.
• The male Mormyrids engage in nest construction by gathering and intertwining aquatic vegetation. This process involves weaving and intertwining plant materials to form a nest structure that is capable of floating on the water’s surface. The vegetation is skillfully arranged and compacted, resulting in a nest that is held together and buoyant.
• The floating nest created by the male Mormyrids possesses a notable feature: the nest’s wall extends several centimeters above the water surface. This elevated wall helps to provide additional protection and stability to the nest. By keeping the wall projected above the water, the nest remains visible and serves as a conspicuous marker for the male’s territory.
• The purpose of constructing a floating nest is primarily for reproductive activities. Once the nest is completed, the male Mormyrids use it as a breeding site. Females are attracted to the nest, and upon entering the male’s territory, they deposit their eggs within the floating structure.
• The floating nest provides a safe and suitable environment for the eggs. The aquatic vegetation used in its construction offers protection against predators and helps maintain the eggs’ position within the nest. The floating nature of the nest also ensures adequate water circulation around the eggs, promoting oxygenation and maintaining suitable conditions for embryonic development.
• The male Mormyrids play a vital role in guarding and maintaining the floating nest. They diligently patrol their territory, defending the nest from potential threats and ensuring the integrity of the structure. This guardianship demonstrates the male’s investment in the survival and well-being of the developing eggs.
• The use of floating nests by male Mormyrids highlights their remarkable adaptation and reproductive behavior. The construction of these nests showcases their ability to utilize available resources and create a specialized habitat for successful egg incubation. The floating nests serve as a remarkable example of the diverse strategies employed by fish species to enhance reproductive success in their natural environments.

(g) Foamy nest

• Certain fish species have developed a unique type of nest known as a foamy nest, which is characterized by the use of bubbles and mucus. The foamy nest provides a safe and suitable environment for the eggs and showcases the remarkable reproductive behavior of these fish species.
• American catfishes are known to construct nests where the eggs are suspended within a mass of bubbles and mucus. The male catfish plays an active role in creating this unique structure. By secreting mucus and agitating the water, the male forms a foam-like mass that contains the eggs. The foam serves as a protective barrier, shielding the eggs from external threats and providing buoyancy.
• Another example of a foamy nest is seen in the male fighting fish, also known as Betta. These fish build nests by blowing bubbles of air and combining them with sticky mucus. The bubbles adhere together, forming a floating mass of foam on the water’s surface. The male fighting fish collects the fertilized eggs in his mouth and gives them a coating of mucus before attaching them to the lower surface of the foamy nest. The male remains on guard, fiercely defending the nest and fighting to the death if necessary.
• Similarly, the male paradise fish, scientifically known as Macropodus, also constructs a foamy nest. In this species, the male creates a similar structure using bubbles and mucus. However, the eggs in the paradise fish are lighter and have the ability to rise up to the nest without the active participation of the father.
• The use of foamy nests by these fish species demonstrates their ability to create specialized environments for the protection and development of their eggs. The foam provides buoyancy and insulation, ensuring the eggs are kept at the appropriate water level and temperature. The mucus coating on the eggs helps prevent them from drying out and provides some level of protection against pathogens.
• The construction and maintenance of foamy nests require significant effort and dedication from the male fish. They invest time and energy in building and defending the nest, showcasing their commitment to reproductive success. The foamy nests serve as a remarkable adaptation and strategy to enhance the survival of the offspring in their natural habitats.
• Overall, the foamy nests built by American catfishes, fighting fish, and paradise fish exemplify the ingenuity and unique reproductive behaviors exhibited by these fish species. These nests provide a fascinating example of the diverse strategies employed by fish to ensure the successful development and survival of their eggs in different aquatic environments.

2. Egg brooding in mouth and intestine

• Egg brooding, specifically through mouth brooding or oral brooding, is a fascinating behavior observed in certain fish species. This behavior involves the stockpiling of eggs or young ones within the fish’s body for a designated period of time.
• One common example of oral brooding can be seen in the Tilapia mossambica, where the female fish takes on the responsibility of brooding the fertilized eggs in her mouth. Initially, the female deposits the eggs in a safe location and invites the male to fertilize them. After the eggs have been fertilized, the male swims away. The female then proceeds to swallow the eggs, trapping them in her buccal cavity (mouth).
• During this brooding period, the female fish stops feeding and solely focuses on caring for the eggs. She occasionally opens her mouth to allow fresh air and water to pass through for the rejuvenation of the eggs. In case of danger, she provides refuge to the young fry within her buccal cavity for a few days after hatching.
• Mouth brooding is also observed in several cichlid species, where the female carries the eggs in her oral cavity. Once the eggs hatch, the fry remain close to the mother’s mouth and can quickly seek refuge inside it if any threat arises. This behavior ensures the protection and survival of the young fry during their early stages.
• In addition to mouth brooding, there are other forms of brooding observed in different fish species. For example, in certain catfish species like Arius, the male fish takes on the role of brooding by carrying the eggs and young ones in his mouth. During this period, the male abstains from feeding and solely focuses on safeguarding the developing eggs and fry.
• Egg brooding in mouth and intestine is a remarkable adaptation seen in various fish species, enabling them to provide parental care and increase the chances of survival for their offspring. This behavior highlights the dedication and commitment of fish parents in ensuring the successful development and protection of their eggs and young ones.

3. Eggs kept in brood pouches

• Eggs kept in brood pouches are a fascinating reproductive strategy observed in various fish species. This method of parental care involves the transfer of fertilized eggs from the female to a specialized pouch where they are protected and nourished until hatching.
• One example of this behavior can be seen in sea horses (Hippocampus). In sea horses, the female transfers the fertilized eggs into the brood pouch located on the lower surface of the male’s abdomen. The male then takes on the responsibility of providing nutrients and oxygen to the developing embryos for several weeks. The brood pouch serves as a protective enclosure, allowing the male to directly care for the eggs and ensure their survival.
• In sea horses, the availability of brood pouches is limited compared to the number of eggs produced by females. Therefore, male sea horses exhibit active mate choice, preferring females with a larger number of eggs that can fill their brood pouch more effectively. Once the eggs hatch, the fry may seek refuge in the pouch when in danger, further emphasizing the importance of this specialized structure for the survival of the offspring.
• Another example of brood pouches can be found in male pipefish (Syngnathus). In these fish, a brood pouch is formed by two flaps of skin on the underside of the body. The female deposits the eggs onto this pouch, and the male takes on the role of protecting and nourishing the developing embryos until they are ready to hatch.
• In the solenostomidae family, specifically, the female’s pelvic fins form the brood pouch. This specialized structure includes numerous long filaments that help keep the eggs in the proper position within the pouch, ensuring their development and survival.
• The presence of brood pouches in these fish species highlights the remarkable adaptations and behaviors that have evolved to ensure the successful reproduction and survival of their offspring. By providing a protected environment and direct parental care, these fish increase the chances of their eggs hatching and their fry reaching a stage of independence.

4. Coiling Round Eggs

• In some fish species, such as the butter fish (Pholis), a unique behavior called “coiling round eggs” is observed. This behavior involves one of the parents, often the male, taking on the responsibility of guarding the eggs by coiling around them.
• After the female butter fish lays her eggs, either on a substrate or within a nest, the male fish assumes the role of protecting the eggs. He accomplishes this by rolling the eggs into a rounded ball shape and then wrapping his body around them. This coiling action forms a protective barrier around the eggs, shielding them from potential threats and predators.
• The male butter fish remains vigilant and dedicated to guarding the egg-ball, ensuring the safety and well-being of the developing embryos. By coiling around the eggs, the male not only provides physical protection but also creates a barrier that helps maintain the eggs’ environmental conditions, such as temperature and oxygen levels.
• This behavior of coiling round eggs in the butter fish is an excellent example of parental care in fish. It demonstrates the commitment of one parent to safeguard the eggs and increase the chances of successful hatching and survival of the offspring. This protective behavior ensures that the eggs receive the necessary care and attention until they are ready to hatch and face the challenges of the external environment.
• Coiling round eggs is just one of the many remarkable adaptations and behaviors exhibited by fish to ensure the survival of their offspring. It highlights the diverse range of strategies that fish employ to maximize their reproductive success and contribute to the overall survival of their species.

5. Depositing eggs in sticky covering

In certain fish species, a fascinating behavior known as “depositing eggs in sticky covering” can be observed. This behavior involves the fish laying their eggs while simultaneously attaching them to various surfaces using a special sticky covering. Here are some examples of this behavior in different fish species:

1. Carps: Carps are known to deposit their eggs with a sticky covering that allows them to attach to each other or to objects like stones, weeds, or other underwater structures. This adhesive covering helps keep the eggs in place and protects them from being swept away by water currents.
2. Yellow perch: The eggs of yellow perch (Perca flavescens) are laid in a distinctive rope-like structure. The eggs are held together by a long, floating membrane, creating a cluster that remains intact and provides some protection against predation.
3. Angler fish: The angler fish, specifically the species Lophius, lays its eggs with a gelatinous external coat. These eggs are deposited in large masses that form a transparent, jelly-like structure. The gelatinous coating not only provides protection but also aids in buoyancy, allowing the eggs to float in the water column.
4. Flying fishes, skippers, garfishes: Some species of flying fishes, skippers, and garfishes secrete a sticky thread-like substance from their kidneys. This sticky substance acts as an adhesive on one end, allowing the eggs to attach to aquatic substrates such as rocks or vegetation. The other end of the thread remains free, enabling some movement for the eggs while keeping them in place.

The act of depositing eggs in a sticky covering serves multiple purposes. Firstly, it helps secure the eggs in a specific location, reducing the risk of dispersal or loss. Secondly, the sticky covering may offer some protection against predators by making it more difficult for them to consume or dislodge the eggs. Lastly, this behavior ensures that the eggs are situated in an environment suitable for their development and survival.

The diversity of methods used by different fish species to attach and protect their eggs through sticky coverings showcases the remarkable adaptations and strategies employed in reproductive behaviors. These behaviors increase the chances of successful egg fertilization, development, and ultimately the survival of the offspring.

6. Depositing Eggs in Suitable Places

Many fish species have evolved various strategies for depositing their eggs in suitable and protected places without the need to build nests. These methods ensure the safety and survival of the eggs in different aquatic environments. Here are some examples:

1. Deposition of eggs in sticky covering: (i) Carps lay their eggs with a special sticky covering that attaches them to each other or to stones, weeds, and other surfaces. (ii) Yellow perch deposit their eggs in a rope-like structure held together by a long floating membrane. (iii) Angler fish lay their eggs invested by a gelatinous external coat, forming a transparent mass of considerable size. (iv) Flying fishes, skippers, garfishes, and similar species secrete a sticky thread-like substance from their kidney. The eggs remain attached to this thread, with one end adhered to an aquatic substrate.
2. Eggs scattered over aquatic plants: Species such as pikes, carps, and Carrassius auratus scatter their eggs over aquatic plants, to which the eggs remain attached.
3. Eggs laid at suitable places: (i) Anadromous fishes, including species like Salmo solar, Acipenser, and Oncorhyncus, lay their eggs in suitable spawning grounds. They excavate pits in gravel substrates, deposit the eggs within the pits, cover them with gravel, and then leave them. (ii) Sand Gobi (Pomatoschistos minutus) lay their eggs in protected places where they are guarded by the male. The male also aerates the eggs through his movement.
4. Eggs deposited on dead shells of bivalves: (i) Females of the cyprinid family deposit their eggs on the dead shells of mussels. (ii) Females of European bitterling (Rhodeus amarus) deposit their eggs in the siphon of a freshwater mussel using a long tube acting as an ovipositor. The male Rhodeus promptly releases sperm over the eggs and guards them. Interestingly, male Rhodeus are not sexually stimulated by the presence of their own species’ females, but rather by the sight of the mussel shell where the eggs have been deposited.

These various strategies for depositing eggs in suitable places showcase the remarkable adaptations and behaviors that fish have developed to ensure the successful reproduction and survival of their offspring. Each method is tailored to the specific needs and environments of the fish species, demonstrating their remarkable diversity and ability to thrive in different aquatic habitats.

7. Scattering eggs over aquatic plants

• In certain fish species, a notable reproductive behavior is the scattering of eggs over aquatic plants. This behavior is observed in fish such as pikes (Esox lucius), carps (Cyprinus carpio), and Carrassius auratus, among others. Instead of depositing their eggs in a consolidated mass or attaching them to specific surfaces, these fish disperse their eggs over aquatic plants, to which they become attached.
• During the breeding season, female fish release their eggs in the water near aquatic vegetation. The eggs are surrounded by a gelatinous coating or adhesive substance that allows them to adhere to the surfaces of plants. This adhesive material helps keep the eggs in place, preventing them from drifting away with water currents.
• By scattering their eggs over aquatic plants, these fish species offer several advantages for the successful development of their offspring. First, the attachment to aquatic plants provides stability and protection for the eggs. The plants offer a secure substrate where the eggs can remain stationary, reducing the risk of being carried away or consumed by predators.
• Additionally, the presence of aquatic plants provides a suitable microenvironment for the eggs. The plants may offer shelter, shade, and a source of nutrients for the developing embryos. They also contribute to maintaining the necessary oxygen levels in the surrounding water, ensuring proper oxygenation for the eggs.
• Scattering eggs over aquatic plants is an adaptive reproductive strategy employed by these fish species. By utilizing the natural structures provided by the plants, they maximize the chances of successful egg development and survival. This behavior also contributes to the dispersion and colonization of fish populations within their freshwater habitats.
• Overall, the scattering of eggs over aquatic plants exemplifies the diverse and fascinating reproductive behaviors exhibited by different fish species. It demonstrates the remarkable adaptations that have evolved to enhance the survival and reproductive success of their offspring in aquatic environments.

8. By the formation of egg capsules

• In the reproductive behavior of oviparous elasmobranchs, such as sharks and rays, the formation of egg capsules plays a crucial role in protecting and nurturing the developing embryos. These species do not give birth to live young but instead produce fertilized eggs that are enclosed in protective structures known as mermaid purses or egg capsules.
• The egg capsules of elasmobranchs are composed of a tough, leathery material often referred to as “horny” or “chondrichthyan” substance. This specialized structure provides mechanical support and acts as a barrier against potential threats, such as predation or physical damage. The exact shape and size of the egg capsules can vary among different species of elasmobranchs.
• After fertilization, the female elasmobranch deposits the fertilized eggs inside these egg capsules. The capsules are then attached to aquatic weeds or other substrates by tendrils or adhesive structures present on the capsules. This attachment ensures that the egg capsules remain in a stable and protected environment during the development of the embryos.
• The egg capsules serve multiple purposes. Firstly, they provide physical protection, shielding the developing embryos from potential predators and external disturbances. Secondly, they create a microenvironment that supports embryonic development. The capsules provide a stable and regulated environment, protecting the eggs from fluctuations in temperature, salinity, and other environmental factors.
• Inside the egg capsules, the embryos undergo development over a period of time. The duration of this developmental process varies depending on the species. As the embryos grow, they obtain nourishment from the yolk sac present within the egg capsules. This yolk sac provides essential nutrients for the embryos until they are ready to hatch.
• The formation of egg capsules in elasmobranchs represents an adaptive reproductive strategy that ensures the survival and development of the embryos. By providing a protected and controlled environment for embryonic growth, these egg capsules enhance the chances of successful hatching and the subsequent survival of the offspring.
• Overall, the formation of egg capsules in oviparous elasmobranchs demonstrates the remarkable adaptations and reproductive strategies employed by these species. It showcases the intricate mechanisms evolved to protect and nurture the developing embryos, increasing their chances of survival in the challenging marine environment.

9. Attachment of eggs to the body

• In certain fish species like Kurtus indicus, a fascinating phenomenon known as the attachment of eggs to the body can be observed. This attachment mechanism involves the male fish developing a bony hook that projects from its forehead, supported by a specialized process of skull bone.
• The eggs of Kurtus indicus are organized into two distinct bunches, and this grouping is facilitated by filamentous processes present on the egg membrane. These filamentous structures help in clustering the eggs together. The unique feature of this species is that the eggs are attached to the bony hook on the male’s forehead.
• As the male fish swims through the water, the eggs are strategically positioned on either side of its head. This placement ensures that one bunch of eggs lies on each side of the male’s head, creating a balanced distribution. The attachment of the eggs to the bony hook allows the male fish to carry and transport the eggs with relative ease.
• This attachment strategy serves multiple purposes. First and foremost, it provides a secure and stable environment for the developing eggs, minimizing the risk of them being dispersed or damaged by external factors. By keeping the eggs close to its body, the male fish can actively protect and guard them against potential predators.
• Additionally, this unique form of egg attachment allows for efficient oxygen and nutrient exchange between the male and the eggs. The proximity of the eggs to the fish’s body ensures that they receive the necessary resources for their development and growth.
• The attachment of eggs to the body in species like Kurtus indicus showcases the diverse and remarkable adaptations that exist in the world of fish reproduction. This strategy exemplifies the evolutionary ingenuity of these organisms in ensuring the survival and well-being of their offspring.

10. Viviparity

Viviparity is a reproductive strategy observed in certain fish species, characterized by internal fertilization and the development of offspring within the oviduct of the female. This form of reproduction involves a high level of parental care and provides maximum protection for the developing embryos.

In viviparous fishes, such as the dogfish (Scoliodon) and the surf fish (Cymatogaster aggregatus), both fertilization and embryo development occur internally within the female’s body. The female retains the fertilized eggs and provides a nurturing environment for their growth. The developing embryos are nourished primarily by a yolk sac placenta, which supplies them with essential nutrients required for their development.

During viviparity, the embryos undergo various stages of development within the oviduct. The female provides the necessary conditions for the embryos to grow and mature. As a result, the young are born with characteristics that resemble those of the adult fish, ensuring their immediate adaptation to the aquatic environment.

Viviparity offers numerous advantages for both the offspring and the parent. The internal development of the embryos allows for better control of environmental factors, such as temperature and water quality, thereby enhancing their chances of survival. The nurturing provided by the yolk sac placenta ensures that the embryos receive sufficient nutrients and oxygen, promoting their healthy development.

Furthermore, viviparity represents the highest degree of parental care among fishes. The female invests significant energy and resources into protecting and nourishing the developing embryos, ensuring their well-being until birth. This form of reproductive strategy contributes to the overall success of the species by increasing the survival rate of the offspring.

In conclusion, viviparity is a remarkable reproductive adaptation observed in certain fish species. It involves internal fertilization, development of the embryos within the oviduct, and nourishment through a yolk sac placenta. Viviparity provides maximum protection, ensures the offspring’s resemblance to the adult form, and represents the highest degree of parental care observed in fishes.

(a) Viviparous Elasmobranchs

• Viviparity is a reproductive strategy observed in various shark species, where the embryos develop within the uterus of the female. This phenomenon is witnessed in more than a dozen shark families and contributes to the high degree of parental care observed in these elasmobranchs.
• In the case of viviparous elasmobranchs like Scoliodon and Mustelus, the eggs undergo development inside the uterus of the female. The uterus is lined with a mucous membrane that forms individual compartments filled with fluid, each accommodating one embryo. These fluid-filled compartments provide a protective environment for the developing embryos, shielding them from external threats and ensuring their survival.
• Nourishment for the developing embryos is provided through a specialized structure known as the yolk-sac placenta. The uterine tissue secretes a substance called embryotrophe or uterine milk, which serves as a nutrient-rich source for the embryos. The embryos receive nourishment from the uterine milk via the yolk-sac placenta, which facilitates the exchange of nutrients and waste products between the mother and the developing embryos.
• The yolk-sac placenta and the uterine milk play crucial roles in supporting the growth and development of the embryos. The uterine milk contains essential nutrients, such as proteins, lipids, and carbohydrates, necessary for the embryos’ proper development. It also helps remove waste materials generated by the embryos.
• The viviparous reproductive strategy in elasmobranchs, including sharks, demonstrates a high level of parental care. The female invests significant energy and resources into providing a safe and nourishing environment for the developing embryos. This ensures their survival and increases the chances of successful offspring production.
• In summary, viviparous elasmobranchs, such as Scoliodon and Mustelus, exhibit a remarkable reproductive adaptation where the eggs develop inside the uterus. The mucous lining of the uterus forms protective compartments for each embryo, and nourishment is provided through the yolk-sac placenta and uterine milk. This viviparous reproductive strategy demonstrates the advanced parental care observed in these shark species, contributing to the survival and success of their offspring.

(b) Viviparous Bony Fishes

• Viviparity, a reproductive strategy where the embryos develop within the female’s body, is not exclusive to elasmobranchs like sharks but can also be observed in certain bony fish species. Viviparous bony fishes, particularly those belonging to the orders Cyprinodonts and Perciformes, exhibit unique reproductive adaptations.
• In teleosts, such as Zoarces, Gambusia, and Poecilia, internal fertilization takes place, and the young ones develop within the ovary. However, unlike viviparous elasmobranchs, the embryos are not attached to the ovary wall. Instead, they develop freely within a sac inside the ovary. This sac, known as the gestational sac or embryonic sac, contains the developing embryos and is filled with an “embryotrophic” material. This material is believed to be produced by the discharged ovarian follicles and provides nourishment to the developing embryos.
• As pregnancy progresses, the gestational sac becomes highly vascularized, allowing for the exchange of nutrients and waste products between the mother and the embryos. This vascularization ensures a continuous supply of nutrients to support the embryos’ growth and development during the months of pregnancy.
• In the case of the shiner-perch (Cymatogaster aggregata), a specific viviparous bony fish species, fertilization of the eggs also occurs within the ovarian follicles. However, the eggs are soon released into the ovary cavity instead of remaining within the follicles. Once released, the eggs are nourished by a secretion from the ovary. This nourishing secretion supports the growth and development of the embryos while they remain in the ovary.
• The young shiner-perch individuals are retained within the ovary until they reach sexual maturity. This unique reproductive strategy allows for extended internal development, ensuring that the offspring have a higher chance of survival and maturity before being released into the external environment.
• Overall, viviparous bony fishes exhibit internal fertilization and various adaptations to support embryonic development within the female’s body. The presence of gestational sacs or ovarian cavities, along with nourishing secretions, highlights the complexity of reproductive strategies in these fish species. These adaptations contribute to increased parental care and enhance the survival and development of the offspring.

(c) Ovo-viviparous

• In the realm of shark reproduction, a unique reproductive strategy known as ovo-viviparity can be observed. This intermediate condition between oviparity (egg-laying) and viviparity (live birth) is exemplified in the nurse shark (Ginglymostoma).
• During ovo-viviparity, the nurse shark’s eggs are covered by a protective horny case within the uterus of the female. The female shark produces eggs internally, and instead of being laid outside the body, the eggs remain inside and undergo development within the uterus. The horny case surrounding each egg provides a protective barrier during the gestation period.
• Within the confines of the uterus, the eggs receive nourishment and oxygen from the mother’s body. This nourishment is delivered through specialized structures such as yolk sacs or placental connections. The development of the embryos progresses within the uterus until they reach a fully developed stage.
• When the time comes for birth, the fully developed young nurse sharks hatch out from their individual eggs within the uterus. They do so by breaking the protective shell that encapsulates each egg. As a result, the newborn sharks are effectively “born” inside the uterus rather than being laid as eggs outside the mother’s body.
• This ovo-viviparous reproductive strategy offers a middle ground between the two extremes of oviparity and viviparity. While the eggs develop internally and receive nourishment from the mother, they are still enclosed within protective cases before hatching. This strategy provides an extra layer of protection for the developing embryos and ensures their survival until birth.
• The ovo-viviparous nature of nurse sharks and other species that employ this reproductive strategy highlights the diversity and complexity of shark reproductive adaptations. It showcases the remarkable ways in which sharks have evolved to give birth to live young, offering them increased protection and improving the chances of survival for their offspring.

11. Concealing Eggs and Young’s in or on their Body

Certain species of fishes have evolved remarkable adaptations to safeguard their eggs and young ones by concealing them in or on their body. These strategies ensure protection and increase the chances of survival for the offspring. Let’s explore some of these methods:

1. Eggs and young concealed in mouth cavity: Some fish species exhibit mouth brooding, where the female carries and protects the fertilized eggs in her mouth. For example, in many cichlids such as Tilapia, the female broods the eggs in her mouth, and after hatching, she allows the young to seek refuge in her buccal cavity during times of danger. Similarly, in marine catfishes like Arius and cardinal fishes, the male carries the eggs and young ones in his mouth, dedicating his energy to parental care and not feeding during this period. The Brazilian cat-fish (Loricaria typus) possesses an enlarged lower lip that forms a pouch for labial incubation, ensuring safety and proper aeration. Even after hatching, the offspring remain close to the father and enter his buccal cavity at the slightest disturbance.
2. Formation of egg ball: In some species like the butter fish (Pholis), the eggs are rolled into a round ball, and one of the parents, often the male, guards the egg ball by curling around it until the young hatch.
3. Eggs attached to cephalic hook: The male nursery fish (Kurtus) of New Guinea demonstrates a unique method of parental care. The male carries a mass of eggs on his forehead, held in a cephalic hook, ensuring their protection and survival.
4. Eggs in integumentary cups: The cat-fish Platystacus of Brazil employs an interesting method where, during the breeding season, the skin on the lower surface of the female’s body becomes soft and spongy. After fertilization, the female presses her body against the eggs, attaching each egg to her skin by a small stalked cup. The eggs remain fixed in these integumentary cups until they hatch.
5. Eggs kept in brood pouches: Several fish species utilize brood pouches for parental care. In sea horses (Hippocampus), the fertilized eggs are transferred by the female into the brood pouch located on the lower surface of the male’s abdomen. The male provides nutrients and oxygen to the eggs during his “pregnancy” period, which lasts several weeks. Male sea horses actively choose mates based on the size and ornamentation of the females, as they need large ones to quickly and sufficiently fill their brood pouches. Male pipefish (Syngnathus) possess a brood pouch formed by two flaps of skin on the underside of their body, onto which the female places the eggs. In the family solenostomidae, the pelvic fins of females form the brood pouch, and numerous long filaments keep the eggs inside the pouch in the proper position.
6. Egg capsules: In oviparous elasmobranchs such as sharks and rays, fertilized eggs are enclosed within protective horny egg capsules called mermaid purses. These capsules, which vary in shape among different groups, are attached to aquatic weeds by their tendrils. The eggs complete their development inside the purse, ensuring their safety until they hatch.

These diverse methods of concealing eggs and young ones in or on the body of fish demonstrate the remarkable adaptations and behaviors that have evolved to ensure the survival and protection of their offspring. By providing a secure environment and direct parental care, these fish species increase the chances of their eggs hatching and their young reaching a stage of independence.

Other Methods of Parental Care in Fishes

Formation of Integumentary Cups

• In the catfish species Platystacus found in Brazil, an intriguing method of parental care can be observed, involving the formation of integumentary cups. During the breeding season, a remarkable transformation occurs in the female fish. The skin on the lower surface of her body becomes soft and spongy, creating a specialized environment for the eggs.
• After the eggs are fertilized, the female fish actively presses her body against the eggs. This pressing action ensures that each individual egg becomes lodged within a small depression in the integument, forming what is known as an integumentary cup. The cup-like structure provides a protective space for each egg.
• To further secure the eggs within the cups, each egg is attached by an inconspicuous stalk. This stalk serves as a connection between the egg and the integumentary cup, preventing the eggs from dislodging or drifting away. The attachment is strong enough to keep the eggs in place but delicate enough to allow for necessary movement and development.
• Once the eggs are firmly positioned inside the integumentary cups, they remain in this protective arrangement until they hatch. The cups provide a stable and sheltered environment for the developing eggs, shielding them from potential harm and external disturbances.
• This unique method of parental care in Platystacus showcases the incredible adaptations and behaviors that fish employ to ensure the survival and successful development of their offspring. The formation of integumentary cups is a remarkable strategy that highlights the intricacies of fish reproductive biology and the diversity of parental care mechanisms observed in nature.

Mermaid’s Purses

• In the realm of oviparous sharks, such as the species Scyllium, a fascinating phenomenon occurs where fertilized eggs are deposited inside protective structures known as mermaid’s purses. These purses, also referred to as egg capsules, are made of a tough and resilient material called horny substance.
• The purpose of these mermaid’s purses is to provide a secure and sheltered environment for the developing embryos. Once the female shark lays her fertilized eggs, they are enclosed within these protective capsules. The capsules feature long tendrils that serve as anchoring mechanisms, attaching them to sea weeds or other suitable substrates.
• The mermaid’s purses remain firmly secured to their anchor points, ensuring that the developing embryos are kept in a stable position. This attachment also helps protect the eggs from drifting away or being displaced by water currents.
• As the embryos continue to develop within the capsules, they eventually reach a stage where they are ready to hatch. At this point, the young sharks use their specialized structures, such as sharp teeth or spines, to rupture the egg case. Through this process, they emerge from the mermaid’s purse and enter the surrounding water.
• The mermaid’s purses play a vital role in safeguarding the eggs and facilitating the development of the embryonic sharks. They serve as a physical barrier against potential predators and environmental hazards, ensuring the survival of the embryos until they are ready to hatch.
• The presence of mermaid’s purses in oviparous sharks exemplifies the remarkable adaptations and reproductive strategies found in marine organisms. These structures not only provide protection but also contribute to the successful continuation of the species by allowing for the safe incubation and hatching of shark embryos.

Care of Independently Swimming Young’s

• In certain fish families such as Gasterosteridae, Centachidae, and Ictaluridae, parental care extends beyond the protection of eggs and encompasses the care of independently swimming young. These fish species go to great lengths to ensure the safety and well-being of their offspring by creating a secure environment away from predators and potential threats.
• As mentioned previously, species like Tilapia, seahorses, and pipefish exhibit parental care by either sheltering their young within the mother’s oral cavity or the father’s brood pouch. This physical closeness provides direct protection to the developing embryos and newborn fry, keeping them safe from harm.
• In the case of cichlid fish, both the male and female contribute to the care of their young. They secrete a nutritious substance from their bodies, often referred to as “parental mucus” or “milk,” which is consumed by the offspring. This substance serves as a nourishing food source, ensuring the young fish receive the necessary nutrients for their growth and development.
• By providing this additional care and nourishment, these fish species increase the chances of survival for their offspring. They actively defend their young ones from potential predators and enemies, safeguarding them until they reach a stage where they can fend for themselves.
• The commitment to caring for independently swimming young reflects the remarkable parental instincts and behaviors observed in various fish families. The provision of protection and nutrition beyond the embryonic stage demonstrates the dedication of these fish parents in ensuring the success of their offspring and the continuation of their species.

FAQ

References

• https://www.sscollegejehanabad.org/study-material/1126279659Parental%20care%20in%20fishes%20(pg)_FishBiology_zoology_narendra.pdf
• http://bgsscienceacademy.ac.in/EducationalNotes/StudyMaterial/UG%20ZOOLOGY/Z5%20Parental%20care%20-%20BGS%20SARC.pdf
• https://www.brainkart.com/article/Extent-and-diversity-of-care—Parental-care-of-Fishes_22274/
• https://www.notesonzoology.com/phylum-chordata/fishes/parental-care-in-fishes-with-diagram-vertebrates-chordata-zoology/8064
• https://www.notesonzoology.com/fish/parental-care-in-fishes-zoology/4464
• https://pcsstudies.com/parental-care-in-fishes/
• https://content.patnawomenscollege.in/zoology/Zoo%20CC305%20Parental%20Care%20in%20Fishes.pdf