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Hormones in Aquacultre/Fish Reproduction

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Hormones in Aquacultre/Fish
Reproduction
Dr. Craig Kasper
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.
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.
Why Induce Fish to Spawn?
• Hybrid production
• Sterile fish (polyploidy)
• Sychronous spawning
(simplifies production)
• Max. production of fry
• Produce fish outside
normal season ($$$!!)
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.
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)
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.
Egg/Sperm Aquisition
1. Tank spawning
2. Hand stripping (taking eggs)
3. Surgically removing the eggs
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.
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.
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!
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
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.)
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!
If you make a mistake…
Sacrificing your broodfish for poor technique is never a good feeling.
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.
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.
Surgical Removal
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.
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).
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)
Hornmone Injection
Brain-hypothalamus-pituitary-gonad
• The internal mechanism that regulates the process of
reproduction in fish is the brain-hypothalamuspituitary-gonad chain (Figure 1).
• The hypothalamus produces
gonadotropin releasing hormone
(GnRH) and also gonadotropin
release inhibiting factors.
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