Aquaculture: Genetics

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AquacultureGenetics

• Dr. Craig Kasper
• FAS 1012

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Genetics What is it?

• Genetics The science of heredity and
  variation.
• Heredity transmission from generation to
  generation (usually through the process of
  reproduction) factors which cause the offspring
  to resemble their parents (or not.)

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Genetics Terms

• Selective breeding-the choosing of individuals of
  a single strain and spp.
• Hybridization-the crossing of different spp.
• Crossbreeding-the mating of unrelated strains of
  the same spp. to avoid inbreeding

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Selective Breeding

• Artifical selection as opposed to natural
  selection, results in reducing genetic
  variability in a population. Could be considered
  inbreeding if not closely monitored.
• If selective breeding involves excessive
  inbreeding physical abnormalities, metabolic
  deficiencies, and developmental abnormalities may
  occur.
• Inbreeding depression-loss of fitness due to
  inbreeding
• more likely to observe occurence of recessive
  traits
• Decrease in heterozygosity

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Selective Breeding

• Although potential for deleterious results,
  selective breeding rationalized by
• size
• color
• shape
• better FCR
• reproductive capacity
• disease resistance

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Hybridization

• Already looked at hybrid striped bass.
• What other examples are out there??
• Splake-brook trout/lake trout, Tiger
  Musky-northern pike/musky
• Sunfish hybrids (many combinations)
• Hopefully achieve hybrid vigor, at least in
  some trait.
• Most true hybrids are sterile, but not all.

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Hormones in Aquaculture

• Hormonal cascade (see handout)
• Importance of Pituitary Gland
• Hypophysectomy removal of pituitary (under
  isotonic growing conditions)
• Pituitary extracts used in some spawning
  practices

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Pituitary Gland - Master Gland

• Linked with hypothalamus of brain
• Produces hormones that affect other endocrine
  tissues - indirect influence
• Produces hormones that
• affect non-endocrine tissues
• directly

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Pituitary Gland

• Indirect influence
• ACTH - adrenocorticotrophic hormone
• stimulates interrenal tissue production of
  cortisol
• TH - thyrotrophic hormone
• stimulate thyroid production of thyroxin (growth,
  metamorphosis-i.e. flounder)
• GTH- gonadotrophic hormone
• stimulates gonads to produce androgens/estrogens

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Pituitary Gland

• Effects non-endocrine tissues directly
• pigmentation - melanophore stimulating hormone
  (MSH)
• affects long-term control of color
• osmoregulation - prolactin, vasotocin
• controls fresh/saltwater systems
• growth somatotrophic hormone
• stimulates gt length, cell multiplication

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Hormones

• Basic concept-a chemical messenger
  (intercellular) released by endocrine glands.
• Hormones in aquaculture
• 1) Human Chorionic Gonadotropin (hCG)
• -mimics endocrine gonadotropins
• -augements serum gonadotropins already present
• -induces ovulation
• -injected IM (often to get multiple broodfish
  to synchronize spawning), chorulon (FDA approved)
• -dosage 50-2000 IU/kg wet weight
• -330 IUs for striped bass and white bass

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Hormones

• 2) Salmon Pituitary Extract (SPE)
• -crude acetone dried preparation of whole
  pituitary
• glands
• -powder
• -natural source of gonadotropins
• 3) Carp Pituitary Extract (CPE)
• Use extracts which are closest phylogenetically
  to fish being injected!

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Hormones

• 4) Leutinizing hormone-releasing hormone
• Gonodotropin Releasing Hormone
• Leutizing Releasing horomoneGnRH
• LHRHaanalog (synthetic) (potent)
• -triggers pituitary to release gonadotropins
• -Intraperitoneal injection (IP)-rapid absoption

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Hormones

• 5) Methyltestosterone (MT)-used under strict
  control
• -accelerates growth rate of some fish (no longer
  used for this purpose)
• -tilapia
• -sex reversal (apply during sexual
  differentiation
• tilapia, walleye, yellow perch
• -can be used to sterilize fish (monosex
  population)
• -can be given orally (food)
• 6) Estradiol
• -all female

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Gynogenesis

• Development of an ovum without fusion of gametes
• usually haploid and die
• sometimes diploid larva develop
• requires retention of 2nd polar body during
  meiosis
• Amazon mollies, cruzian carp do this
• Induced by
• radition, chemical, electrical currents, sperm
  from related species

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Sex reversal

• Genotypic females turned into phenotypic males
  (MT)
• sex-reversed (XX) males cross with normal females
  yields all female
• Polyploidy
• triploid fish (involves retention of 2nd polar
  body, but fertilized by normal sperm)
• essentially 2 sets of chromosomes from female,
  one from male

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Intersexed fish

• Hermaphrodites-contain ovotestes, can go either
  way...
• MT treatment female after sex determination
  occurs (ovary has already started to develop)
• intersexed fish must be killed to determine if
  the process work! Not very good for aquaculture?

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Questions??