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
  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 environmental conditions and cues are
  correct for the target species.

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Hormones/Fish

• Hormone induced spawning of fish is nearly 75
  years old!
• Surprisingly, many techniques havent 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 modification of what was already being
  done.

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Why Induce Fish 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 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.

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Sexual Maturity Revisited

• Ensuring the sexual maturity of your fish is
  important.
• Males can be checked or milt easily, but females
  are 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
  the spawning tank following injection(s).
• Brood fish should not be disturbed and subdued
  lighting is 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 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.

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Tank Spawning 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
  (ltinjury).
• Less labor required!

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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
  checking for 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 do this.
• Anatomy of some fish wont allow efficient strip
  spawning.
• For example, sturgeon and paddlefish have no
  ovarian sac the eggs are released into the
  abdominal 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 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.

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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 diatoms
  damage eggs).

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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 recipe and mixing instructions see SRAC
  handout 426)