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)