Hormones in Aquacultre/Fish Reproduction Dr. Craig Kasper Introduction вЂў New inovative hatchery techniques have evolved as global demand for fish increases. вЂў Many fish spawn in environments that are nearly impossible to simulate in a hatchery. вЂў Hormone-induced spawning is the only reliable method to induce reproduction in these fishes. вЂў Now fish may be spawned nearly any time of year providing environental conditions and cues are correct for the target species. Hormones/Fish вЂў Hormone induced spawning of fish is nearly 75 years old! вЂў Surprisingly, many techniques havenвЂ™t changed much during this period. вЂў Fish such as carp, catfish, seabass, redfish and snook were used as test fish. вЂў Induced spawning for many other fish became merely a modificaiton of what was already being done. Why Induce Fish to Spawn? вЂў Hybrid production вЂў Sterile fish (polyploidy) вЂў Sychronous spawning (simplifies production) вЂў Max. production of fry вЂў Produce fish outside normal season ($$$!!) Fish Handing вЂў Of course be careful!! REM: These are broodfish and money is at stake! вЂў Fish should be captured, handled and spawned with the greatest care possible. (Females will reabsorb eggs if roughed up!) вЂў Optimal environmental conditions are required to maximize spawning potential. Sexual Maturity Revisited вЂў Ensuring the sexual maturity of your fish is important. вЂў Males can be checked for milt easily, but females are more difficult (may require a microscope) Environmental Conditions вЂў photoperiod вЂў water temperature вЂў water quality (e.g., dissolved oxygen, pH, hardness, salinity, alkalinity) вЂў flooding and water current вЂў tides/lunar cycles вЂў weather cycles (e.g., atmospheric pressure, rainfall) вЂў spawning substrate (e.g., aquatic plants, sticks, gravel, mats, caverns) вЂў nutrition вЂў disease and parasites вЂў presence of other fish. Egg/Sperm Aquisition 1. Tank spawning 2. Hand stripping (taking eggs) 3. Surgically removing the eggs 1. Tank Spawning w/hormones вЂў Simplest method for obtaining a hatchery spawn. вЂў Brood fish of both sexes are placed together in the spawning tank following injection(s). вЂў Brood fish should not be disturbed and subdued lighting is recommended. (Frank Sinatra doesnвЂ™t hurtвЂ¦) вЂў The female ovulates when she is physiologically ready. вЂў Male will stimulate the female to release eggs. Tank SpawningвЂ¦ вЂў Fertilization improved if males are preconditioned (injected prior). вЂў Males can be used for several tank spawns. вЂў Two or three males/female/tank can be used to ensure fertilization. (unless aggressive) вЂў If tank size permits, then more вЂњgroupsвЂќ may be in one tank. Tank Spawnig Advantages вЂў Skilled workers (predicting the exact time of ovulation or checking females) вЂў Verifying ovulation is unnecessary вЂў Rapid deterioration of eggs in the ovary after ovulation is not a problem. вЂў Unnecessary to check and strip the fish (<injury). вЂў Less labor required! Tank Spawning Disadvantages вЂў Egg collector or suitable spawning substrate needed вЂў Dirt/debris with the eggs, or egg clumping = fungus вЂў Some females may not release all their eggs! вЂў Estimation of fecundity difficult. вЂў CanвЂ™t used method for polyploidy Hand Stripping вЂў Also a common technique. вЂў Broodfish kept separate. вЂў Ovulation verified when eggs flow freely from the vent (most spp.) (or with ultrasound!) вЂў One hour prior to anticipated spawning females are checked again. вЂў Tropical species every 45 minutes or less, temp.) Hand strippingвЂ¦ вЂў The fish is turned belly up and gentle finger pressure is applied to the abdomen starting at the pectoral fins, moving slowly toward the vent. вЂў Do not try to squeeze or force the eggs from the fish (injury)! вЂў If you only get a few eggs, then put вЂ�er back! She ainвЂ™t ready! If you make a mistakeвЂ¦ Sacrificing your broodfish for poor technique is never a good feeling. Hand Stripping вЂў Water canвЂ™t touch the eggs at this point!! вЂў Water activates sperm and closes the micropyle (hole where sperm enter egg.) For many fish, this closure takes place within only 45 to 60 seconds. вЂў Solution: Keep a towel handy! вЂў Stripping of eggs used the same technique as checking for вЂњripeness.вЂќ Firm pressure and steady flowing motions are better than driving them out with force. Surgical Removal вЂў Yes, sometimes it becomes necessary to do this. вЂў Anatomy of some fish wonвЂ™t allow efficient strip spawning. вЂў For example, sturgeon and paddlefish have no ovarian sac; the eggs are released into the abdominal cavity during ovulation. Surgical Removal Fertilization вЂў Once youвЂ™ve got the eggs, repeat the same вЂњstrippingвЂќ technique with a male fish. вЂў Milt can be added to eggs and them slightly aggitated by swirling, mixing with glass rod, or turkey feather. вЂў Next add some water. Hardening of the eggs will occur within several minutes in some spp. вЂў Move eggs to the appropriate McDonald jar, etc. Sticky Eggs? вЂў In the wild, eggs stick together or adhere to substrate, but in the hatchery this isnвЂ™t desirable. вЂў Silt-clay вЂў Bentonite вЂў FullerвЂ™s Earth вЂў Diatomaceous Earth is bad (sharp edges of diatoms damage eggs). Sticky EggsвЂ¦ вЂў The silt-clay suspension (saturated) is combined with fertilized eggs at 2 to 4 parts suspension to 1 part fertilized eggs. (~20 minutes) вЂў Other options: Tannic acid Urea and salt Sodium sulfite (for receipe and mixing instructions see SRAC handout #426) Hornmone Injection Brain-hypothalamus-pituitary-gonad вЂў The internal mechanism that regulates the process of reproduction in fish is the brain-hypothalamuspituitary-gonad chain (Figure 1). вЂў The hypothalamus produces gonadotropin releasing hormone (GnRH) and also gonadotropin release inhibiting factors.