Induced Breeding In Fishes – Principle, Mechanism, Procedure, Advantages

What Is Induced Breeding (hypophysation)?

• Induced breeding, also referred to as hypophysation, is a technique used in aquaculture to stimulate fish to breed under controlled conditions. This process is especially important for species that naturally reproduce in free-flowing waters, like rivers, but face challenges breeding in confined environments such as ponds or tanks. By injecting hormones—often pituitary extracts or synthetic alternatives—into mature, ripe fish, the process triggers their gonads to release eggs and sperm, facilitating reproduction.
• This method was first successfully applied to Indian major carps in the 1950s, and has since become a cornerstone of modern fish farming, particularly for species like mrigal (Cirrhinus mrigala), rohu (Labeo rohita), and catla (Catla catla). In the wild, these species breed in the rainy season when they migrate to shallow, flooded regions of rivers. In captive settings, however, the absence of the natural ecological stimuli required for spawning means they cannot reproduce without assistance. Therefore, external hormones are used to induce this process.
• Historically, fish culturists relied on the collection of seeds (fertilized eggs) from rivers, which was labor-intensive and often led to mixed batches containing unwanted species. Induced breeding overcomes this challenge by providing a reliable, quality-controlled method to ensure the production of high-quality fish stock in hatcheries. By managing reproduction in controlled environments, hatcheries can focus on enhancing genetic traits and improving the survival rate of the fish.
• Induced breeding has been especially critical in regions like India, where fish, particularly major carps, play a vital role in nutrition and economic livelihood. With India ranking second in global farmed fish production, methods like induced breeding are essential to meet the growing demand. These fish provide essential nutrients like proteins, omega-3 fatty acids, and amino acids, making them a crucial component of human diets.
• Besides improving the quality of fish stock, induced breeding has transformed aquaculture by reducing dependence on the unpredictable and often unsustainable practice of natural seed collection. As fish farmers have more control over breeding cycles, they can plan and optimize fish production, which is key to ensuring food security and sustaining fisheries management.

History of induced breeding

Induced breeding has played a transformative role in aquaculture, enabling the controlled reproduction of fish species that naturally require specific environmental stimuli for spawning. The history of this technique highlights key advancements across different countries, leading to its widespread adoption in modern fish farming.

• 1930, Argentina – Houssay:
  The concept of induced breeding began in Argentina in 1930, when Houssay successfully used pituitary extract to stimulate viviparous fish to give premature birth. This groundbreaking work laid the foundation for further exploration into manipulating fish reproduction.
• 1934, Brazil:
  Four years later, Brazilian researchers achieved success with induced breeding using pituitary extract. This step demonstrated the technique’s viability for broader application beyond Argentina.
• Adoption in America and Russia:
  Soon after, the technique spread to other regions. American researchers like Merlin and Hubs, and Russian scientist Gerebilisky, embraced induced breeding as a method to enhance fish production, pushing forward the global research in aquaculture.
• 1937, India – Khan’s First Success:
  In India, the first recorded success with induced breeding was achieved by Khan in 1937, who worked with Cirrhinus mrigala. This marked the introduction of the technique in Indian fisheries and would later serve as a foundation for further advancements.
• 1955, Dr. Hiralal Choudhuri’s Contribution:
  In 1955, Dr. Hiralal Choudhuri experimented with minor carps such as potasi (Pseudeotropius atherinoides) and Indian flying barb (Esomus danricus), utilizing induced breeding to spawn these species under controlled conditions.
• 1956, Ramaswamy and Sunderaraj – Induced Breeding of Catfish:
  Ramaswamy and Sunderaraj pioneered induced breeding in catfish species like magur (Clarias batrachus) and singhi (Heteropneustes fossilis) in 1956, further demonstrating the versatility of the technique for diverse fish species.
• 1957, Major Milestone – Dr. Hiralal Choudhuri and Major Carps:
  A landmark achievement occurred in 1957 when Dr. Hiralal Choudhuri successfully induced the breeding of major carps such as Cirrhinus mrigala, C. reba, and Labeo rohita. This success represented a significant breakthrough in aquaculture, enabling the controlled breeding of economically important fish species in India.
• 1960, Indian Major Carps – Pituitary Extract and Synthetic Hormones:
  Following the success in the 1950s, Indian major carps were induced to spawn using injections of pituitary extract or synthetic hormones (gonadotropic hormones), refining the induced breeding process further.
• 1963, Parameswaran and Alikunhi – Breeding Chinese Carps:
  The success of Parameswaran and Alikunhi in 1963 with exotic Chinese carps like grass carp (Ctenopharyngodon idella) and silver carp (Hypophthalmichthys molitrix) marked another significant advancement. Their work demonstrated the global potential of induced breeding for increasing fish production and diversifying the species available for aquaculture.

Principle of Induced Breeding (hypophysation)

Induced breeding, or hypophysation, is a controlled reproductive technique used to stimulate fish to spawn under captive conditions. This method is especially important in aquaculture to breed species that naturally require specific environmental stimuli to reproduce. The process uses hormone injections to artificially trigger the natural reproductive cycle of fish. Here’s a detailed breakdown of the principle behind induced breeding:

• Environmental Factors → Brain:
  In a natural setting, environmental factors such as temperature, light, and water conditions signal the brain to initiate reproductive processes. These cues are vital for the release of necessary hormones.
• Brain → Hypothalamus (Releasing Hormone):
  In response to the environmental signals, the brain activates the hypothalamus, which secretes releasing hormones. These hormones play a critical role in signaling the next stage of the reproductive process.
• Hypothalamus → Pituitary Gland (Gonadotropic Hormones – FSH & LH):
  The releasing hormones stimulate the pituitary gland to release two key gonadotropic hormones: Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH). These hormones are essential for initiating and regulating the development and maturation of the fish’s reproductive organs.
• Pituitary Gland → Gonads (Gonadotropic Hormones):
  Once the FSH and LH hormones are released, they act on the gonads (ovaries in females, testes in males). These hormones accelerate the maturation of eggs in females and sperm in males.
• Gonads → Gametes (Spawning):
  The final step in the process involves the release of mature gametes (eggs and sperm). In response to the hormone signals, the fish undergoes spawning, where eggs and sperm are released into the water for fertilization.

Events of natural breeding

Natural breeding in fish involves a complex interaction of environmental and biological factors that trigger the reproductive process. For many cultured farm fishes, including Indian major carps, natural breeding can be difficult in captive conditions due to the absence of these environmental triggers. However, in the wild, a range of stimuli and conditions lead to successful reproduction.

• Environmental Factors:
  • Environmental elements such as photoperiods (day length), rainfall, temperature, and water flow play a critical role in fish reproduction. These factors affect the pituitary gland’s hormonal activity, leading to the release of gonadotropins that regulate the maturation of the gonads in both males and females.
  • Indian major carps typically spawn in submerged river areas during the monsoon season when fresh floods clear terrestrial life and promote the growth of microflora and microfauna, which serve as food for the fry and fingerlings.
• Spawning Conditions:
  • Spawning occurs in natural settings where conditions such as water currents and the influx of fresh rainwater create optimal environments for fish to lay eggs. These natural phenomena are difficult to replicate in static water bodies like ponds or lakes, which explains why many species, including major carps, struggle to reproduce in confined conditions.
  • Any disruption in these environmental conditions—such as changes in temperature, water quality, or flow—can hinder hormonal secretions in captive environments, preventing fish from naturally reproducing.
• Hormonal Control:
  • The pituitary gland in fish is a key endocrine organ that regulates reproductive processes. Located in the brain, the pituitary gland secretes hormones like Follicle Stimulating Hormone (FSH) that trigger the development and maturation of reproductive organs. Once the gonads mature, spawning is initiated.
  • In natural settings, the correct environmental cues ensure the proper secretion of these hormones, facilitating the reproductive cycle. However, in captivity, these natural signals may be absent, leading to the need for induced breeding techniques that replicate the hormonal triggers artificially.

Mechanism of induced breeding

Induced breeding is a crucial technique in aquaculture, enabling the controlled reproduction of fish species. This process typically involves hormone injections that stimulate spawning in mature breeders. The administration of pituitary extracts, derived from donor fish, is the most widely utilized method for this purpose. The mechanism of induced breeding unfolds through a systematic series of steps that ensures successful spawning, ultimately leading to the collection of fertilized eggs for cultivation. Below are detailed descriptions of each step in the mechanism of induced breeding.

1. Selection of Breeders: The success of induced breeding hinges on the careful selection of healthy, mature fish. Ideal breeders are typically medium-sized, aged between two and four years, and weigh between 1-5 kg. Breeders should be collected from their natural habitats prior to the breeding season and housed in fertilization ponds. The selection process emphasizes identifying fully ripe males and females. Male fish exhibit roughened pectoral fins and release milt when pressure is applied to their abdomens. Ripe females have soft, rounded bellies, with swollen, pinkish vents.
2. Segregation of Breeders: To achieve a high fertilization rate, synchronization of ovulation and milt release is critical. This necessitates segregating males and females prior to breeding, allowing for optimal timing when the fish are injected with hormones. The health of the breeders must be maintained throughout this period. Measures include treating any injuries with a dilute potassium permanganate (KMnO₄) solution and regular monitoring for pathogens. Maintaining suitable water conditions tailored to the species selected is essential during this phase.
3. Stocking of Breeders: Stocking involves placing breeders in designated ponds or bundhs, which are specially designed to mimic natural spawning environments. These ponds should support optimal spawning conditions and are stocked at a density of 1000-2000 per hectare. The fish can be procured from natural sources, either by collecting eggs or juvenile stages (spawn, fry, and fingerlings) from local rivers during the appropriate seasons.
4. Maintenance of Breeders: Breeders are fed a diet of rice bran and oil cakes, constituting approximately 1% of their body weight daily. Regular monitoring of their health and maturation status is vital. Breeders are typically segregated by sex to facilitate controlled breeding when hormones are administered.
5. Extraction of the Pituitary Gland: The pituitary gland, a critical source of hormones for induced breeding, is collected from donor fish. This extraction can be performed either through the foramen magnum or by dissecting the skull. The former method is generally preferred due to its efficiency and the ability to utilize the fish head afterward. Care must be taken to avoid damaging the gland during extraction.
6. Storage of the Pituitary Gland: After collection, the pituitary glands must be preserved to retain their potency. Common preservation methods include freezing the glands, storing them in absolute alcohol, or using acetone. Each of these methods effectively dehydrates the gland while maintaining its hormonal activity for future use.
7. Preparation of Pituitary Extract: The preserved glands are then processed to create a pituitary extract suitable for injection. The dosage depends on the recipient’s size and maturity level. The glands are ground with a small volume of distilled water or saline, centrifuged, and the supernatant is used for administration.
8. Injection of Pituitary Extract: The extract is administered via intramuscular injection, typically in the region of the caudal peduncle. Proper dosages vary, with females generally receiving two doses—initially 2-3 mg/kg followed by 5-8 mg/kg after six hours. Males receive a single dose of 2-3 mg/kg. Post-injection, the breeders are placed in breeding hapas or cisterns to facilitate spawning.
9. Spawning Observation and Egg Collection: Following the second injection, breeders typically spawn within six hours, often during the night. Eggs are monitored for fertilization quality; fertilized eggs are clear and buoyant, while unfertilized ones appear opaque. The fertilized eggs are carefully collected and transferred to hatching hapas for incubation.
10. Hatching and Transfer of Hatchlings: After a specified incubation period, hatchlings emerge from fertilized eggs and are subsequently transferred to the outer section of the hatching hapa. The inner section retains the unhatched shells, while the outer section houses the active hatchlings.

Procedure of induced breeding technique

1. Collection of Pituitary Gland from Fish

The pituitary gland, a crucial component for induced breeding, is collected from a mature fish known as the donor fish. One of the most commonly used donor species is the common carp (Cyprinus carpio) due to its year-round breeding cycle, ensuring a constant supply of mature individuals. Collecting the pituitary gland requires precise handling and can be achieved through two primary methods.

• Collection of Glands from the Foramen Magnum:
  • The first step involves uncovering the foramen magnum by carefully removing the vertebral parts attached to the skull.
  • Using forceps, the surrounding fat is removed, often aided by cotton pieces for cleaning.
  • Two forceps are inserted dorsally into the foramen magnum, allowing the anterior part of the brain to be detached.
  • The remaining brain portion is carefully lifted through the foramen magnum, exposing the pituitary gland.
  • The gland is identified and then gently removed without causing any damage.
• Collection of Glands by Dissecting Heads:
  • This method is preferred for its efficiency and economical advantage, as the fish heads can still be used for consumption.
  • The head is dissected using a sharp butcher’s knife, making a clean cut to remove part of the scalp.
  • Fat surrounding the brain is removed with the help of cotton.
  • Next, the olfactory and optic nerves are severed, allowing the brain to be lifted out of the skull.
  • The pituitary gland can either come out with the brain or remain attached to the brain cavity floor, often covered by a thin membrane.
  • In both cases, the gland is carefully extracted, ensuring it remains intact and undamaged.

2. Preservation of Gland

Preservation of the pituitary gland is a critical step following its collection, ensuring that the gland remains viable for future use in induced breeding procedures. The gland must be preserved properly to maintain the integrity and potency of the gonadotropins required for stimulating reproduction in fish. Various methods of preservation are employed depending on the region and specific requirements.

• Immediate Storage in Absolute Alcohol:
  • Once the pituitary gland is collected, it is immediately placed in sterile vials or bottles filled with absolute alcohol (ethanol).
  • This method is widely used in India, as ethanol provides an effective means to preserve the gland for extended periods, typically for up to a week or longer if needed.
  • The sterile environment and alcohol solution help to prevent any microbial contamination or degradation of the gland.
• Acetone-Dried Preservation:
  • In temperate regions such as the USSR and USA, the acetone-dried method is commonly used for preservation.
  • In this process, the pituitary gland is dehydrated using acetone, which effectively removes water and prevents the breakdown of tissue.
  • This method allows for long-term storage and is particularly useful when glands need to be preserved for an extended period.
• Freezing Method:
  • Freezing is another technique employed for gland preservation. By freezing the glands, enzymatic activity is halted, which helps to maintain the gland’s potency.
  • This method can preserve the gland for a more extended duration, especially when immediate use is not required.
• Glycerine Preservation:
  • In certain cases, glycerine is used as a preservative for pituitary glands.
  • Glycerine creates a protective environment for the gland, preventing its desiccation and maintaining its structural integrity.

3. Preparation of Hormonal Extract from Pituitary Gland

Preparation of the hormonal extract from the pituitary gland is an essential step in induced breeding. This extract, derived from donor fish, is prepared carefully to ensure it retains its gonadotropic hormones, which stimulate spawning in mature breeders. The preparation process is straightforward yet requires precision at each stage to maximize the effectiveness of the extract.

• Measurement of Pituitary Gland:
  • The process begins by measuring the required amount of pituitary glands based on the total body weight of the fish intended for breeding.
  • This quantity is carefully calculated to ensure the hormonal dosage aligns with the body weight of the recipient fish.
• Drying of Pituitary Gland:
  • After collection, the pituitary gland is dried using blotting paper to remove excess moisture.
  • Proper drying ensures that the gland does not lose potency when processed further.
• Homogenization of the Gland:
  • Once dried, the gland is transferred into a tissue homogenizer.
  • A small quantity of distilled water is added, and the gland is homogenized to break it down into a fine solution.
  • The dilution ratio of the gland extract should be carefully controlled, typically set at 0.2 ml of extract per kilogram of fish body weight.
• Centrifugation:
  • The homogenized gland solution is then centrifuged. This process separates the solid gland tissue from the liquid extract.
  • After centrifugation, the supernatant—the clear liquid portion—contains the active hormones and is used for injection.
  • The solid residue is discarded, ensuring that only the purified hormonal extract is utilized for inducing spawning.

4. Brooders Selection

Brooder selection is a crucial step in the process of induced breeding, as the success of spawning depends heavily on selecting healthy, mature, and fully ripe brooders. Proper selection ensures that hormonal treatments will lead to effective ovulation or spermiation, resulting in successful fertilization.

• Maturity and Health:
  • Brooders must be fully mature and in good health for effective breeding. Selecting fish that are too young or not in peak physical condition can result in unsuccessful breeding efforts.
  • Typically, fish between the ages of 2 to 4 years are selected for breeding, as they are generally at the optimal age for reproductive performance.
• Body Weight:
  • The preferred body weight of selected fish ranges from 1 to 5 kilograms. This weight range typically indicates that the fish are large and healthy enough to contribute a significant quantity of eggs or sperm.
• Identification of Male and Female Brooders:
  • Clear differentiation between male and female brooders is essential for successful pairing. The following characteristics are commonly used to identify mature male and female Indian carps:
  • Male Characteristics:
    • The inner surface of the pectoral fin feels rough to the touch.
    • The abdomen of the male is narrow and firm.
    • The vent, or genital region, appears whitish and is recessed or inward.
    • When the abdomen is gently pressed, milt (sperm) is released.
  • Female Characteristics:
    • The inner surface of the pectoral fin is smooth.
    • The abdomen is soft, bulging, and larger than that of the male.
    • The vent is pinkish in color and protruded outward.
    • When the abdomen is pressed, eggs are released, indicating that the female is fully ripe and ready for spawning.

5. Injection to the Brooders

In the process of induced breeding, injecting brooders with hormonal extracts is a key technique to stimulate spawning. The hormones, usually derived from the pituitary glands of donor fish, are administered to induce ovulation in females and spermiation in males. The method of injection, dosage, and timing are critical for ensuring the success of the breeding program.

• Homoplastic Injection:
  • In this method, the hormonal extract from the pituitary gland of one fish species is injected into another closely related species within the same group.
  • For instance, the pituitary extract from one carp species can be used to induce breeding in another carp species.
• Heteroplastic Injection:
  • This technique involves injecting hormonal extract from the pituitary gland of one species into a more distantly related species.
  • An example would be using pituitary extract from catfish to induce breeding in carps, or vice versa.
• Process of Injection in Fishes:
  • Correct Dosage Determination:
    • Determining the appropriate dosage of the pituitary gland extract is vital. The amount administered depends on the size, weight, and maturity of the brooders. Additionally, the state of maturity of the donor fish is a factor in determining the hormone concentration in the extract.
  • Injection Methods:
    • The pituitary extract is administered to the brooders using a hypodermic syringe. The injection can be either intramuscular (into the muscle) or intraperitoneal (into the abdominal cavity).
    • Intramuscular injections are preferred for their ease and safety, while intraperitoneal injections, though occasionally used, are avoided by less experienced hands due to the risk of puncturing internal organs such as the heart.
  • Dosage and Timing:
    • Female fish typically receive two doses of hormone injections. The first, known as the preliminary dose, is usually 2-3 mg/kg of body weight and is administered to prepare the female for the final hormonal surge. Male fish, on the other hand, do not receive this preliminary dose.
    • After an interval of about 6 hours, a second dose is administered to the female, with an increased concentration of 5–8 mg/kg of body weight, which directly stimulates ovulation.
    • Males receive a single dose of 2-3 mg/kg of body weight, usually timed with the second dose given to the female. The precise dosage may vary based on factors such as the age, sex, and maturity of the fish, as well as environmental conditions.
  • Injection Sites:
    • For intramuscular injections, the fish is laid on its side in a hand net, and the needle is inserted into the caudal peduncle (the base of the tail) or the shoulder region.
    • For intraperitoneal injections, the needle is inserted near the base of the paired pectoral fins. However, this method requires caution, as less experienced hands can risk puncturing critical organs such as the heart. Therefore, intramuscular injections are generally preferred due to their safer administration.

6. Spawning

Spawning is a critical phase in fish breeding, particularly when utilizing hormonal induction techniques. Following hormone injections administered to both male and female brooders, spawning is facilitated in a specially prepared environment known as a breeding hapa. This process is essential for the production of fertilized eggs, which are vital for successful aquaculture operations.

• Breeding Setup:
  • Brooders are released into a breeding area, typically a circular breeding hapa, immediately after hormone injections.
  • A standard set of brooders consists of one female fish accompanied by two males to enhance fertilization chances.
  • The breeding hapa is a box-shaped enclosure constructed from fine mesh materials, such as marking cloth or mosquito netting.
  • The fine mesh design allows for proper water circulation while preventing the escape of fish eggs and milt, thus ensuring successful fertilization.
• Dimensions and Configuration:
  • The average dimensions of a breeding hapa are approximately 3 meters x 1.5 meters x 1 meter, which accommodates brooders weighing between 3 to 5 kg.
  • It is important for the hapa’s height to remain around 20 centimeters above the water level to prevent suffocation of fish seedlings.
  • The hapa is enclosed on all sides, but the roof can be left open or closed based on specific environmental conditions.
• Behavioral Changes:
  • Within 2-3 hours after administering the second hormonal injection, both male and female fish exhibit increased activity and excitement.
  • Males engage in vigorous behavior, swimming towards females and pressing against them with their snouts, which is a precursor to spawning.
• Timing of Spawning:
  • Spawning typically occurs 3-6 hours after the second injection, often peaking around midnight if the injection is administered in the evening.
  • Optimal conditions for hormonal injection include cooler, cloudy weather, which has been shown to yield better results.
• Fertilization Process:
  • The spawning event results in the release of fertilized eggs, which are then carefully transferred to hatching hapas for incubation.
  • Fertilized eggs of species like Osteobarma belangeri are characterized by a crystalline, transparent, and pearl-like appearance, allowing them to rise to the surface with slight water movement.
  • In contrast, unfertilized eggs appear opaque or whitish, indicating that fertilization has not occurred.
• Factors Affecting Spawning Success:
  • The success rate of spawning is influenced by several factors, including the effectiveness of the hormonal inducement and the type of inducing agent used. This highlights the importance of precise technique and knowledge in aquaculture practices.

Role of other natural and synthetic hormones in induced breeding

The role of natural and synthetic hormones in induced breeding is paramount in aquaculture, facilitating the controlled reproduction of various fish species. Hormonal induction enhances spawning success rates and allows for the manipulation of reproductive cycles, thereby contributing to sustainable fish farming practices.

• Types of Hormones Used:
  • Gonadotropin-Releasing Hormone (GnRH) Analogues: These hormones are pivotal in stimulating reproductive processes. They are often used in conjunction with dopamine antagonists to enhance their efficacy.
  • Synthetic Hormones: Due to the challenges associated with the preparation and preservation of natural pituitary extracts, various synthetic hormones have emerged as viable alternatives. Examples include:
    • LHRH-a (Luteinizing Hormone-Releasing Hormone agonist): Utilized in conjunction with domperidone, LHRH-a effectively induces oocyte maturation and ovulation, particularly in species such as the bighead carp (Aristichthys nobilis).
    • Human Chorionic Gonadotropin (HCG): Known for its ability to induce ovulation, HCG offers several advantages, including:
      • Cost-effectiveness and availability in a purified form.
      • Enhanced stability, contributing to a longer shelf life.
      • Studies indicate that HCG can successfully induce spawning in fish such as Labeo rohita at doses of 600 IU/kg body weight and in silver carp with doses ranging from 630-660 IU.
• Additional Synthetic Hormones:
  • WOVA-FH: This synthetic gonadotropin-releasing hormone analogue (SGnRH) has shown efficacy in inducing breeding across various fish species, including Indian major carp, exotic carp, and catfish. SGnRHs provide a robust means of manipulating reproductive activities in aquaculture settings.
  • Ovatide: An endemic hormone that is both cost-effective and highly efficient in inducing breeding, Ovatide is employed for major carps with varying doses, such as:
    • 0.20-0.40 ml/kg for Rohu and Mrigal.
    • 0.20-0.30 ml/kg for Catla.
    • The use of Ovatide can yield fertilization and hatching rates between 85-95%.
  • Synahorin: This hormone combines chorionic gonadotropin with mammalian pituitary extract and has demonstrated effectiveness when paired with pituitary extracts in inducing spawning. However, it has not proven successful as a standalone treatment for species like rohu.
  • Ovaprim: Recognized as a modern analogue of gonadotropin hormones, Ovaprim serves as an effective substitute for pituitary gland extracts. Key observations regarding Ovaprim include:
    • It often results in higher egg production rates, with notable increases from 1.15 lakh to 1.41 lakh eggs in rohu when compared to pituitary extract use.
    • Fertilization and hatching rates tend to be superior with Ovaprim, leading to larger eggs after water hardening, indicative of more advanced development.
    • Spawning response times for Ovaprim are comparable to traditional pituitary treatments, yet hatchlings derived from Ovaprim treatment generally appear healthier, although further validation is warranted.
    • Recommended dosages for various species include:
      • 0.40-0.50 ml/kg for Catla.
      • 0.30-0.40 ml/kg for Labeo rohita.
      • 0.25-0.30 ml/kg for Mrigal.
      • 0.50-0.70 ml/kg for silver and grass carps.
      • For male fish, effective doses typically range from 0.10 to 0.20 ml/kg.
    • Notably, post-spawning mortality rates for brooders treated with Ovaprim are minimal, attributed to reduced handling compared to traditional methods.
• Storage and Handling:
  • One of the significant advantages of Ovaprim is that it can be stored at room temperature, eliminating the need for refrigeration, thereby simplifying handling protocols in aquaculture operations.

Factors influencing induced breeding

The factors influencing induced breeding in fish are multifaceted and interconnected, playing critical roles in the success of aquaculture practices. Understanding these elements is essential for enhancing breeding outcomes. Below are the key factors that impact induced breeding, explained in detail:

• Favorable Climatic and Hydrological Conditions:
  • Optimal environmental conditions, including temperature, light, and water quality, significantly increase the likelihood of successful breeding.
  • Conversely, poor choices in breeders, incorrect dosages of pituitary extracts, and adverse climatic conditions often lead to breeding failures.
  • For instance, extreme heat, high salinity, or excessive sunlight typically hinder the breeding process.
• Light:
  • Light exposure significantly influences fish reproduction, with photoperiods affecting maturation and spawning.
  • Certain species exhibit varying responses to light; for example, Salvelinus fontinalis matures earlier under shorter light periods but experiences delayed maturation under prolonged exposure.
  • In India, Cirrhinus reba also demonstrates earlier maturity in daylight, indicating the critical role of light in reproductive cycles.
• Temperature:
  • The relationship between environmental temperature and sexual maturation is well-documented.
  • Optimal temperature ranges exist for different species, with deviations leading to unsuccessful breeding.
  • For example, Indian major carps typically breed within a temperature range of 24°C to 37°C, with an optimum around 27°C. Breeding success diminishes significantly above 30°C.
  • Higher temperatures may enhance gonadal ripening and stimulate spawning, while lower temperatures post-injection provide favorable conditions for fertilization and embryonic development.
• Dissolved Oxygen (DO₂):
  • High levels of dissolved oxygen are critical for the hatching process, as many fish species require elevated oxygen levels for successful reproduction.
  • Water that is low in oxygen often inhibits breeding behavior; therefore, water renewal and aeration are essential for stimulating reproductive activities.
• Water Current and Rain:
  • The rheotactic response, or the inclination of fish to swim in the direction of water flow, is a well-established behavior influencing spawning.
  • Rain plays a pivotal role, especially for major carps, as it stimulates spawning even in the presence of hormonal injections.
  • The relationship is evident: increased monsoons lead to higher rainfall, resulting in stronger water currents, which in turn promote maturation and gonadal activity.
• Cloudy Weather:
  • Many fish species tend to spawn more successfully during cloudy or rainy days, particularly following heavy rainfall.
  • Cooler temperatures and reduced light intensity during these conditions create an ideal environment, enhancing fish activity and breeding readiness.
• pH Levels:
  • The pH of the water significantly influences breeding, particularly among carp species.
  • Successful breeding generally occurs within an alkaline pH range, underscoring the importance of maintaining appropriate water chemistry for optimal reproductive outcomes.

Examples of natural and synthetic hormones use in induced breeding of fishes

The use of natural and synthetic hormones in the induced breeding of fish represents a significant advancement in aquaculture practices. This approach enhances the efficiency of fish reproduction, making it essential for sustaining fish populations and supporting fisheries. The introduction of various hormone extracts has improved the methods of artificial breeding, achieving high levels of success. Below is a detailed examination of the primary hormones and their roles in induced breeding.

• Human Chorionic Gonadotropin (HCG):
  • HCG is a glycoprotein hormone produced by the placenta during pregnancy, appearing in high concentrations in urine.
  • When administered to mature fish, HCG promotes gamete maturation and release.
  • Its efficacy in inducing ovulation and sperm release is significantly enhanced when combined with pituitary gland extracts, rather than being used alone.
• Sumaach and Synahorin:
  • Developed by INFAR (India) Ltd., these products are cost-effective alternatives to pituitary extracts with extended shelf lives.
  • The preparation involves grinding the product in distilled water (2 mg in 0.2 ml) and centrifuging the mixture to obtain a supernatant for injection.
  • A two-step injection process is employed: the first injection is given to the female, followed by a simultaneous injection to both sexes. The doses are weight-dependent, with optimal results achieved using fully ripe breeders under favorable environmental conditions.
• Synahorin:
  • This preparation consists of chorionic gonadotropin and mammalian hypophysial extract, contributing to the hormonal regulation of fish reproduction.
• Ovaprim (Salmon Gonadotropin RH):
  • Ovaprim is a formulation of salmon gonadotropin releasing hormone (RH) combined with a dopamine antagonist, stabilizing the solution in glycerin and alcohol.
  • Research by Dr. Richard Peter highlighted that dopamine inhibits gonadotropin synthesis and release from the pituitary gland in fish.
  • By disrupting the inhibitory signal, Ovaprim facilitates gamete release. Dosage recommendations are 0.3 to 0.5 mg/kg for females and 0.01 to 0.3 mg/kg for males.
  • It has shown superior results in various Indian states, yielding significantly higher egg production compared to pituitary extracts, with notable stability under tropical conditions.
• Pimozide and LHRH-A:
  • Pimozide functions as a dopamine antagonist and enhances the ovulatory effects of LHRH-A, particularly effective for Indian major carps.
  • LHRH and its analogue are advantageous for brackish water fish species, although current formulations are short-lived, necessitating the development of longer-lasting alternatives.
• DOCA (II-Desoxycorticosterone-acetate):
  • This hormone has shown effectiveness in inducing ovulation and egg maturation in catfish species, particularly Clarias and Heteropneustes.
  • Its dual role in both maturation and ovulation distinguishes it from other hormone preparations.
• Antiestrogen Tamoxifen:
  • This compound has been beneficial for coho salmon, especially when used in conjunction with a primer such as pituitary extract.
  • It exemplifies the diversity of hormonal treatments available for optimizing fish breeding practices.

Substitutes of fish pituitary gland

The use of fish pituitary gland extracts has been a traditional method for inducing breeding in aquaculture. However, several substitutes have emerged that offer various advantages, including effectiveness and practicality. Understanding these substitutes is crucial for improving breeding success rates in fish. The following points detail the main substitutes for fish pituitary gland extracts:

• Human Chorionic Gonadotropin (HCG):
  • HCG, particularly from Organon, has demonstrated efficacy in inducing spawning in species like silver carp. When administered alone, HCG has been successful, and its effectiveness is enhanced when used in conjunction with carp pituitary extracts. This dual approach capitalizes on the synergistic effects of both hormones, leading to improved spawning outcomes.
• Synahorin:
  • Synahorin is another substitute that, when combined with carp pituitary gland extracts, has successfully induced breeding in both rohu and silver carp. However, it has shown limited efficacy when used alone in rohu, indicating that while it can be beneficial, its effectiveness may depend on the species and specific hormonal interactions. This suggests a need for further research to optimize its application in induced breeding.
• Ovaprim:
  • Ovaprim is a relatively newer hormone preparation designed specifically as a substitute for fish pituitary extracts. While it may be more expensive, Ovaprim has proven to be significantly more effective than carp pituitary extracts in inducing spawning across various carp species. Its unique formulation enhances its ability to stimulate reproductive processes, making it a valuable tool for aquaculturists aiming for high breeding success rates.

Problems of hypophysation technique

The hypophysation technique, widely employed in aquaculture for induced breeding, has encountered several challenges that can hinder its effectiveness and practicality. Understanding these problems is crucial for improving breeding strategies and enhancing fish production. Below are the key issues associated with the hypophysation technique:

• Measurement of Potency:
  • Farmers face difficulties in accurately measuring the potency of the available pituitary glands. This lack of standardization complicates the administration of appropriate dosages for effective breeding, leading to inconsistent results in spawning success.
• Collection and Storage Challenges:
  • Large-scale collection and storage of pituitary glands pose serious logistical issues. The process requires careful handling and preservation to maintain the viability of the glands. As a result, many farms may struggle to acquire sufficient quantities for their breeding programs, thereby limiting their operational capacity.
• Supply and Demand Gap:
  • There exists a significant disparity between the supply and demand for pituitary glands in aquaculture. This gap can lead to shortages, compelling farmers to resort to alternatives that may not be as effective. Consequently, this inconsistency can adversely affect the overall productivity of fish farming operations.
• Lack of Basic Equipment:
  • Many aquaculture facilities lack essential equipment, such as chemical balances, centrifuges, and refrigerators, which are critical for processing and utilizing pituitary extracts effectively. The absence of this equipment can impede the proper application of the hypophysation technique, resulting in lower breeding success rates.
• High Market Costs:
  • The cost of pituitary glands in the market is often prohibitively high. This financial burden can deter farmers, particularly small-scale operations, from utilizing this technique. Consequently, the high costs associated with hypophysation may limit its widespread adoption and utilization in aquaculture practices.

Advantages of induced breeding

Induced breeding offers several advantages that significantly enhance the efficiency and effectiveness of fish farming practices. By manipulating reproductive processes, aquaculture practitioners can achieve desirable outcomes that are often unattainable in natural conditions.

• Targeted Species Selection: Induced breeding allows for the spawning of specific fish species, effectively reducing the presence of unwanted or invasive fish populations in culture ponds. This targeted approach ensures that only the desired species are cultivated, optimizing resource use and management.
• Consistent Supply on Demand: One of the primary benefits of induced breeding is the ability to provide a reliable and timely supply of fish spawn. Unlike wild conditions, where breeding times can be unpredictable, induced breeding enables hatcheries to meet market demands consistently, ensuring a steady flow of fish stock.
• Seasonal and Flexible Supply: Induced breeding provides the flexibility to produce fish seedlings according to varying market demands throughout different seasons. This adaptability is crucial for aquaculture businesses, allowing them to synchronize production with consumer needs, thereby enhancing economic viability.
• Reduced Holding Period: By employing induced breeding techniques, there is no longer a need to maintain potential male and female spawners in captivity for extended periods while waiting for natural spawning events. This reduction in holding time conserves space and resources, streamlining management practices in aquaculture facilities.
• Ease of Implementation: The techniques involved in induced breeding are relatively straightforward, making them accessible to practitioners without extensive technical training. This simplicity encourages broader adoption within the aquaculture sector, as farmers can learn and implement these methods effectively.
• Cost-Effectiveness: Induced breeding generally incurs lower costs compared to traditional methods of collecting fish spawn from natural sources. The economic advantage lies in the reduced labor, time, and resources required to produce viable fish stock, which ultimately enhances profitability for aquaculture operations.
• Enhanced Control Over Reproduction: Induced breeding allows aquaculture managers to exert greater control over the reproductive cycles of fish. This control is crucial for improving production efficiency, ensuring that spawning occurs at optimal times to maximize yield.

Precautions for Induce Breeding

Precautions for induced breeding in fish are essential for maximizing the chances of successful spawning while minimizing health risks. Proper management of breeding conditions and careful handling of breeders contribute significantly to effective aquaculture practices. The following points outline critical precautions to consider:

• Disease and Parasite Prevention:
  • To minimize the risk of diseases and parasitic infections, maintaining a biosecure environment is crucial. This includes regular monitoring of water quality and fish health.
• Breeder Preparation:
  • Breeders should be thoroughly cleaned using a potassium permanganate (KMnO₄) solution for a few minutes before induction. This step is vital for disinfecting the fish and reducing potential pathogen loads.
• Protection from Mechanical Injury:
  • During handling, breeders must be shielded from mechanical injuries. Gentle handling techniques should be employed to prevent physical stress and damage, which could adversely affect breeding outcomes.
• Optimal Water Conditions:
  • Water conditions must be conducive to spawning, with optimal temperatures ranging from 24°C to 31°C. This temperature range facilitates metabolic activities necessary for gamete maturation and release.
  • Additionally, water turbidity should be monitored, ideally maintained between 100 and 1000 ppm, as this range supports a suitable environment for breeding.
• Flowing Water with High Dissolved Oxygen:
  • Utilizing flowing water with elevated levels of dissolved oxygen (DO) enhances the breeding environment. High DO levels are crucial for the metabolic processes involved in spawning and embryonic development.
• Light Intensity and Duration:
  • The intensity and duration of light exposure are significant factors influencing induced breeding and spawning. Optimal lighting conditions stimulate reproductive behaviors and hormonal responses in fish.
• Use of Compatible Pituitary Gland Extracts:
  • When using pituitary gland extracts for induced breeding, it is advisable to select glands from the same species or closely related species as the recipient fish. Such extracts are known to be more effective in promoting gamete release.

Why does fish not breed in captivity?

The inability of certain fish species, particularly many cultured farm fish like Indian Major Carps (IMC), to breed in captivity poses significant challenges in aquaculture. Understanding the underlying reasons for this phenomenon is crucial for enhancing breeding practices and improving fish production. The following points detail the primary factors contributing to the lack of breeding in captivity:

• Environmental Influence:
  • Many fish species rely on specific environmental cues to trigger breeding behaviors. Factors such as rainfall, temperature, and water current play a vital role in influencing hormonal activity related to reproduction. These environmental triggers are often absent or insufficient in captive settings.
• Hormonal Regulation:
  • The hormonal release from the pituitary gland and gonads is critical for reproductive success. In natural habitats, changes in environmental conditions stimulate the appropriate hormonal responses, leading to breeding. However, disturbances in the captive environment can disrupt this hormonal release, resulting in insufficient hormonal levels necessary for successful breeding.
• Impact of Poor Nutrition:
  • The availability and quality of food significantly affect the maturation of fish ovaries. In captivity, fish may not receive adequate nutrition or sufficient natural foods, which can hinder the development of reproductive organs and overall breeding success.
• Exposure to Contaminants:
  • The presence of biocides and other pollutants in captive environments can negatively impact the health and reproductive capabilities of fish. These substances can lead to hormonal imbalances and impair the maturation of gonads, further preventing successful breeding.
• Stress Factors:
  • Captive environments may introduce stressors that do not exist in the wild, such as limited space, unnatural social structures, and handling procedures. Stress can adversely affect the physiological processes involved in reproduction, further inhibiting breeding behaviors.
• Lack of Natural Stimuli:
  • In natural environments, fish experience a variety of stimuli that promote breeding, including seasonal changes and the presence of suitable habitats for spawning. In captivity, the absence of these natural cues can lead to a failure in initiating breeding behaviors.

Why induced breeding is necessary for fish culture?

The following points outline the necessity of induced breeding in aquaculture:

• Purity of Spawn: Induced breeding ensures the collection of pure spawn from specific fish species. In contrast, spawn collected from natural water sources is often contaminated with undesirable wild species, which can adversely affect the quality of cultivated fish. Therefore, induced breeding allows for the elimination of these undesirable species, promoting healthier populations.
• Timeliness of Seed Availability: The availability of fish seed in natural environments is unpredictable and varies with environmental conditions. Induced breeding provides a reliable and timely supply of pure seeds, allowing fish farmers to meet market demands efficiently. This capability is especially critical in commercial aquaculture, where timing can significantly influence profitability.
• Scalability of Production: Induced breeding can fulfill varying quantities of seed demand at any given time. This flexibility allows fish farmers to scale their operations according to market needs, thus optimizing production levels and ensuring a consistent supply of fish.
• Simplicity of Technique: The methods employed in induced breeding are generally straightforward and do not require extensive technical expertise. This accessibility makes it feasible for individuals without specialized training to learn and implement the techniques effectively. Consequently, it democratizes fish farming, enabling a broader range of practitioners to participate in aquaculture.
• Cost-Effectiveness: Induced breeding is a cost-efficient alternative to traditional methods of spawn collection, which often involve significant expenditures associated with wild harvesting. The lower costs associated with induced breeding not only make it economically viable for fish farmers but also enhance overall profitability.
• Control Over Breeding Conditions: Induced breeding allows aquaculturists to manipulate environmental conditions to optimize spawning outcomes. By regulating factors such as temperature, light, and water quality, fish farmers can enhance reproductive success rates, leading to increased yields.
• Enhancement of Desired Traits: Through induced breeding, fish farmers can selectively breed for desirable traits, such as growth rate, disease resistance, and feed conversion efficiency. This selective breeding contributes to the development of superior fish strains that can thrive in cultivated environments.

Why induced breeding? – Significance of induced breeding

The significance of induced breeding arises from several key factors that influence fish reproduction, particularly in controlled environments.

• Environmental Factors: Natural breeding in fish is often regulated by various environmental conditions, such as photoperiod, rainfall, temperature, and water currents. These factors can trigger hormonal responses in fish that lead to spawning. In aquaculture, replicating these natural cues can be challenging. Therefore, induced breeding provides an effective solution to overcome these limitations by creating optimal conditions for spawning in captivity.
• Hormonal Stimulation: In captive environments, the release of hormones necessary for spawning may be insufficient due to the lack of natural stimuli. Induced breeding compensates for this deficiency by utilizing hormonal injections, such as gonadotropins or synthetic analogs, which stimulate the gonads to release gametes. Consequently, this technique enhances the likelihood of successful fertilization and increases spawn viability.
• Nutritional Considerations: The availability of natural foods plays a significant role in the maturation of fish gonads. In captivity, fish may not have access to the same variety or quantity of natural food sources that they would encounter in the wild. Insufficient nutrition can impede the reproductive process, leading to suboptimal spawning outcomes. Induced breeding allows for the provision of adequate nutrition while simultaneously stimulating gamete release, thereby improving reproductive performance.
• Controlled Breeding Cycles: Induced breeding allows for the synchronization of breeding cycles among fish populations. This synchronization is crucial for managing hatcheries and ensuring a steady supply of juvenile fish. By controlling the timing of spawning events, aquaculturists can better plan for subsequent stages of production, such as larval rearing and grow-out phases.
• Enhancement of Production Efficiency: Induced breeding is instrumental in increasing the overall efficiency of fish production. It enables fish farmers to meet market demands by ensuring a reliable and consistent supply of high-quality juvenile fish. Moreover, it reduces reliance on wild-caught fish for broodstock, thereby contributing to the sustainability of fish populations.
• Broodstock Management: The ability to induce breeding in a controlled environment also allows for better management of broodstock. Fish can be selectively bred to enhance desirable traits, such as growth rates, disease resistance, and adaptability. This selective breeding contributes to the development of robust fish strains that are better suited for aquaculture.
• Reduction of Environmental Impact: By facilitating controlled breeding in aquaculture settings, induced breeding can help reduce the pressure on wild fish populations. Sustainable practices such as induced breeding contribute to the conservation of natural resources and the maintenance of ecological balance.