Hormones in Aquacultre/Fish Reproduction

1. Hormones in Aquacultre/Fish Reproduction Dr. Craig Kasper

2. Introduction • New inovative hatchery techniques have evolved as global demand for fish increases. • Many fish spawn in environments that are nearly impossible to simulate in a hatchery. • Hormone-induced spawning is the only reliable method to induce reproduction in these fishes. • Now fish may be spawned nearly any time of year providing environental conditions and cues are correct for the target species.

3. Hormones/Fish • Hormone induced spawning of fish is nearly 75 years old! • Surprisingly, many techniques haven’t changed much during this period. • Fish such as carp, catfish, seabass, redfish and snook were used as test fish. • Induced spawning for many other fish became merely a modificaiton of what was already being done.

4. Why Induce Fish to Spawn? • Hybrid production • Sterile fish (polyploidy) • Sychronous spawning • (simplifies production) • Max. production of fry • Produce fish outside normal season ($$$!!)

5. Fish Handing • Of course be careful!! REM: These are broodfish and money is at stake! • Fish should be captured, handled and spawned with the greatest care possible. (Females will reabsorb eggs if roughed up!) • Optimal environmental conditions are required to maximize spawning potential.

6. Sexual Maturity Revisited • Ensuring the sexual maturity of your fish is important. • Males can be checked for milt easily, but females are more difficult (may require a microscope)

7. Environmental Conditions • photoperiod • water temperature • water quality (e.g., dissolved oxygen, pH, hardness, salinity, alkalinity) • flooding and water current • tides/lunar cycles • weather cycles (e.g., atmospheric pressure, rainfall) • spawning substrate (e.g., aquatic plants, sticks, gravel, mats, caverns) • nutrition • disease and parasites • presence of other fish.

8. Egg/Sperm Aquisition 1. Tank spawning 2. Hand stripping (taking eggs) 3. Surgically removing the eggs

9. 1. Tank Spawning w/hormones • Simplest method for obtaining a hatchery spawn. • Brood fish of both sexes are placed together in the spawning tank following injection(s). • Brood fish should not be disturbed and subdued lighting is recommended. (Frank Sinatra doesn’t hurt…) • The female ovulates when she is physiologically ready. • Male will stimulate the female to release eggs.

10. Tank Spawning… • Fertilization improved if males are preconditioned (injected prior). • Males can be used for several tank spawns. • Two or three males/female/tank can be used to ensure fertilization. (unless aggressive) • If tank size permits, then more “groups” may be in one tank.

12. Tank Spawnig Advantages • Skilled workers (predicting the exact time of ovulation or checking females) • Verifying ovulation is unnecessary • Rapid deterioration of eggs in the ovary after ovulation is not a problem. • Unnecessary to check and strip the fish (<injury). • Less labor required!

13. Tank Spawning Disadvantages • Egg collector or suitable spawning substrate needed • Dirt/debris with the eggs, or egg clumping = fungus • Some females may not release all their eggs! • Estimation of fecundity difficult. • Can’t used method for polyploidy

14. Hand Stripping • Also a common technique. • Broodfish kept separate. • Ovulation verified when eggs flow freely from the vent (most spp.) (or with ultrasound!) • One hour prior to anticipated spawning females are checked again. • Tropical species every 45 minutes or less, temp.)

16. Hand stripping… • 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. • Do not try to squeeze or force the eggs from the fish (injury)! • If you only get a few eggs, then put ‘er back! She ain’t ready!

17. If you make a mistake… Sacrificing your broodfish for poor technique is never a good feeling.

18. Hand Stripping • Water can’t touch the eggs at this point!! • 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. • Solution: Keep a towel handy! • Stripping of eggs used the same technique as checking for “ripeness.” Firm pressure and steady flowing motions are better than driving them out with force.

19. Surgical Removal • Yes, sometimes it becomes necessary to do this. • Anatomy of some fish won’t allow efficient strip spawning. • For example, sturgeon and paddlefish have no ovarian sac; the eggs are released into the abdominal cavity during ovulation.

20. Surgical Removal

21. Fertilization • Once you’ve got the eggs, repeat the same “stripping” technique with a male fish. • Milt can be added to eggs and them slightly aggitated by swirling, mixing with glass rod, or turkey feather. • Next add some water. Hardening of the eggs will occur within several minutes in some spp. • Move eggs to the appropriate McDonald jar, etc.

22. Sticky Eggs? • In the wild, eggs stick together or adhere to substrate, but in the hatchery this isn’t desirable. • Silt-clay • Bentonite • Fuller’s Earth • Diatomaceous Earth is bad (sharp edges of diatoms damage eggs).

23. Sticky Eggs… • The silt-clay suspension (saturated) is combined with fertilized eggs at 2 to 4 parts suspension to 1 part fertilized eggs. (~20 minutes) • Other options: • Tannic acid • Urea and salt • Sodium sulfite • (for receipe and mixing instructions see SRAC handout #426)

24. Hornmone Injection

25. Brain-hypothalamus-pituitary-gonad • The internal mechanism that regulates the process of reproduction in fish is the brain-hypothalamus-pituitary-gonad chain (Figure 1). • The hypothalamus produces gonadotropin releasing hormone (GnRH) and also gonadotropin release inhibiting factors.