hormones in aquaculture fish reproduction
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Hormones in Aquaculture/Fish
Reproduction
Dr. Craig Kasper
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Introduction
New innovative hatchery techniques have evolved asglobal 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 methodto induce reproduction in these fishes.
Now fish may be spawned nearly any time of yearproviding environmental conditions and cues are correctfor the target species.
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Hormones/Fish
Hormone induced spawning of fish is nearly 75 yearsold!
Surprisingly, many techniques havent changed much
during this period.
Fish such as carp, catfish, seabass, redfish and snookwere used as test fish.
Induced spawning for many other fish became merely amodification of what was already being done.
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Why InduceFish to Spawn?
Hybrid production
Sterile fish (polyploidy)
Synchronous spawning
(simplifies production)
Max. production of fry
Produce fish outside
normal season ($$$!!)
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Fish Handing
Of course be careful!! REM: These arebroodfish and money is at stake!
Fish should be captured, handled and spawnedwith the greatest care possible. (Females willreabsorb eggs if roughed up!)
Optimal environmental conditions are required tomaximize spawning potential.
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Sexual Maturity Revisited
Ensuring the sexual maturity of your fish isimportant.
Males can be checked or milt easily, but femalesare more difficult (may require a microscope)
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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.
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Egg/Sperm Acquisition
1. Tank spawning
2. Hand stripping (taking eggs)
3. Surgically removing the eggs
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1. Tank Spawning w/hormones
Simplest method for obtaining a hatchery spawn.
Brood fish of both sexes are placed together in thespawning tank following injection(s).
Brood fish should not be disturbed and subdued lightingis recommended. (Frank Sinatra doesnt hurt)
The female ovulates when she is physiologically ready.
Male will stimulate the female to release eggs.
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Tank Spawning
Fertilization improved if males arepreconditioned (injected prior).
Males can be used for several tank spawns.
Two or three males/female/tank can be used toensure fertilization. (unless aggressive)
If tank size permits, then more groups may bein one tank.
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Tank Spawning Advantages
Skilled workers (predicting the exact time of ovulation orchecking females)
Verifying ovulation is unnecessary
Rapid deterioration of eggs in the ovary after ovulation isnot a problem.
Unnecessary to check and strip the fish (
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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.
Cant used method for polyploidy
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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.)
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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 aint ready!
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If you make a mistake
Sacrificing your broodfish for poor technique is never a good feeling.
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Hand Stripping
Water cant 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 checkingfor ripeness. Firm pressure and steady flowing motions
are better than driving them out with force.
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Surgical Removal
Yes, sometimes it becomes necessary to dothis.
Anatomy of some fish wont allow efficient stripspawning.
For example, sturgeon and paddlefish have noovarian sac; the eggs are released into theabdominal cavity during ovulation.
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Surgical Removal
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Fertilization
Once youve got the eggs, repeat the same stripping
technique with a male fish.
Milt can be added to eggs and them slightly agitated byswirling, 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.
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Sticky Eggs?
In the wild, eggs stick together or adhere to substrate,but in the hatchery this isnt desirable.
Silt-clay
Bentonite
Fullers Earth
Diatomaceous Earth is bad (sharp edges of diatomsdamage eggs).
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Sticky Eggs
The silt-clay suspension (saturated) is combinedwith fertilized eggs at 2 to 4 parts suspension to1 part fertilized eggs. (~20 minutes)
Other options:
Tannic acid
Urea and salt
Sodium sulfite(for recipe and mixing instructions see SRAC
handout #426)