Fish Reproduction Brian Peterson, M'S'

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Fish ReproductionBrian Peterson, M.S.
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Objectives

• Aquaculture and its role in the U.S. and Idaho
• Female reproductive system
• -Ovary and follicle anatomy
• Sex determination and hermaphorditism
• Alligator production in Idaho
• Research at the U of I

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1999 Census Catches 1 Billion in Sales

• Aquacrop Value ()
• Catfish 488,000,000
• Trout 77,000,000
• Salmon 100,000,000
• Ornamental 69,000,000
• Source Economic Research Service, USDA

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Fish Farming vs Cattle Ranching

• Fish farming is the fastest growing sector of the
  world food economy.
• -Growing 11/year
• -13 million tons produced in 1990 to 34.4
  million tons in 1999.
• Cattle ranching hit high of 53 million tons in
  1990.
• -Surpass cattle ranching as a food source by the
  end of this decade.

Source World Catch News
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Rainbow Trout Production 1999

• Idaho currently ranks 1 in the nation in RBT
  production- 48 of total sales
• 76 of market size fish
• 2)North Carolina 4.5 million lbs
• 3)California 2.3 million lbs
• 1999 Idaho produced 47.5 million fish which
  equates to 46 million lbs
• 1999 total sales of RBT- 37 million
• Source Economic Research Service, USDA

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Terms to Know

• TeleostFish that exclude jawless fish,
  cartilaginous fish, lobe-finned fish, and
  sturgeon.
• VitellogeninGlycolipoprotein produced in the
  liver and accumulated in the oocyte as yolk.
• VitellogenesisProcess of yolk formation.

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Female Reproductive System

• Hypothalamus, pituitary, ovary, and liver.
• In all species, oogonia proliferate in the
  ovary, become oocytes, undergo vitellogenesis,
  maturation, and ovulation.
• Endocrine controls of the system begin with
• 1.) hypothalmic responses to environmental cues
• photoperiod and temperature

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Female Reproductive System

• 2.) hypothalmic responses to proximal cues like
  substrate type, courtship behaviors, and
  pheromones.
• Ultimately these cues influence gonadotropin
  releasing hormone (GnRH) that stimulates GTH-I
  and GTH-II.

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Role of GTH-I and GTH-II

• Ovarian and testicular function is controlled by
  GTH-I and GTH-II (glycoprotein heterodimers).
• GTH-I/GTH-II contain a common alpha subunit and a
  distinct beta subunit conceived to be FSH-and
  LH-like.
• GTH-I important for vitellogenesis, early
  gonadal development, and elicits the production
  and storage of GTH-II.
• GTH-I secreted during the early phases of
  ovarian development.

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Role of GTH-II and GnRH

• GTH-II stimulates events leading to final
  oocyte maturation and ovulation in females and
  spermiation in males.
• GTH-IIstimulated by GnRH, NE, and NPY
• inhibited by DA
• In teleosts, multiple GnRH molecules may be
  expressed simultaneously with different
  functions.
• GnRH mRNA levels can be influenced by many
  factors state of sexual maturation,
  photoperiod, and sex steroids.
• Indicates that GnRH is controlled by internal and
  external factors.

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Delivery of hypothalmic hormones

• How is GnRH delivered to the gonadotrophs in the
  pituitary gland?
• In mammals a hypothalamohypophysial portal system
  is present.
• In cartilaginous, salmonid fishes, and others no
  portal system exists. GnRH delivered by direct
  innervation of all portions of the pituitary.

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Changes in levels of GTH-I and GTH-II in coho
salmon during reproductive maturation
GTH-II
GTH
GTH-I
M
O
N
A
A
M
S
J
J
Vitellogenesis Ovulation
Adapted from Dickoff and Swanson, 1990
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Ovary Anatomy

• Teleost ovarian structure is classified into two
  forms gymnovarian and cystovarian
• Gymnovarian ovaries are possessed by most bony
  fishes except (salmonids).
• Lack a true ovarian cavity.
• Characterized by ovigerous folds which lie
  exposed to the peritoneal cavity.
• Oocytes are ovulated into the coelom and moved
  into the oviduct by ciliated epithelium.

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Ovary Anatomy

• Cystovarian ovaries (salmonids) have a true
  ovarian capsule.
• Oocytes are ovulated into the intraovarian space
  and move down to the cloaca without entering the
  peritoneal cavity by ciliated epithelium or
  smooth muscles.

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A section through a cystovarian ovary showing
ovigerous folds and location of oocytes
Adapted from Turner, 1983
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Gymnovarian
Cystovarian
Bilobed
Bilobed
Mesonephric Kidneys
Mesonephric Kidneys
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Follicle Anatomy

• Ovarian follicle consists of a developing oocyte
  and two surrounding cells layers.
• Innermost layer steroidogenic granulosa cells
  Outer layer thecal layer (fibroblasts, collagen
  fibers, capillaries, and steroidogen special
  theca cells).

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Diagrammatic representation of the follicle and
oocyte during early vitellogenesis
Nagahama, 1983
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Oocyte Recruitment

• Three modes of oocyte development in teleosts
• Synchronous- all oocytes develop synchronously
  and ovulate at the same time.
  Ex Pacific Salmon (semelparous)
• Group-synchronous- vitellogenic oocytes are
  divided into groups, which ovulate over the
  course of one breeding season.
• Ex RBT (iteroparous)

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Oocyte Recruitment

• Three modes of oocyte development in teleosts
• Asynchronous- oocytes at all developmental stages
  are present in the ovary.
• Ex Tropical fish

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Mechanisms of Sex Determination

• I. Recombination of sex chromosomes at
  fertilization
• a. Chromosomal genotype
• Mammals and most fish Male XY
• FemaleXX
• Birds and some fish MaleZZ
• FemaleZW

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Sex Determination/Development

• b. H-Y Antigen
• 1. Male specific antigen present on the
  surfaces of cells
• XYH-Y antigen
• Old theory suggested H-Y antigen existed in
  fish--Not true
• 2. Can be used to sex embryos in mammals
• 3. Does not cause male development

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Sex Determination/Development

• SRY Gene
• Located on the Y chromosome of mammals and NOT
  FISH
• Stimulates male development
• Produces Testis Determining Factor (TDF)
• FISH--Male/female development is regulated by
  genetic and hormonal control

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Sex Determination/Development

• Development of the gonads, reproductive tract and
  external phenotype
• a. Origin of gonads
• Fish are similar to mammals in that the male and
  female start with an undifferentiated gonad
• Mesonephros (Primative kidney)
• Ovary and testis arise from this undifferentiated
  gonad-PGC migrate from yolk sac to the genital
  ridge--Mechanism is unclear in fish

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Sex Determination/Development

• b) Origin of reproductive tract
• Two duct system
• Mullerian ducts--female reproductive
  tract-oviducts, uterus, cervix and vagina
• Wolffian ducts--male reproductive
  tract-epididymis, vas deferens, seminal vessicles
• FISH--tubular extension of the gonad

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Mechanisms of Sex Determination

• II. Temperature-dependent sex determination
• Alligators and turtles have no heteromorphic pair
  of chromosomes-sex is determined by temperature
• Example-Alligators-lays 40-45 eggs (65 days to
  hatch)
• 93oF-All F
• 86oF-All M
• 88oF-Half F and half M

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Alligator Production

• Alligators are being grown in southern ID
• Young alligators are grown in tanks at 85-90oF
  year- around-grow at a rate of 2 inches per month
• Alligators are harvested at 3 yrs old (5 feet
  long)
• Skins sold for 30/ft
• Meat sold for10-20/lb

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Mechanisms of Sex Determination

• III. Behavior sex determination
• Social situations can initiate changes in gonadal
  sex.
• Example-(Marine fish) Sex change is initiated by
  removal or addition of dominant male or female to
  a population.
• Mechanism of action is unclear!
• However, GnRH-cells in the preoptic area of the
  brain increase.

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Hermaphroditism in Fish

• c. Three forms of hermaphroditism in fish
• 1. Protogynous hermaphroditism-individuals
  develop first into females and turn later into
  males-Ex (Clown Fish)
• 2. Protandrous hermaphroditism- individuals
  develop first into males and turn later into
  females
• -Marine fish

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Hermaphroditism in Fish

• 3. Synchronous hermaphroditism-Both male and
  female states coexist functionally
• -Sea bass (self fertilization)

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Research at University of Idaho

Hypothalamus
SS (-)
GHRH ()
Anterior Pituitary
GH
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My Research

• Release patterns of GH in fish.
• Somatostatin role in GH release.
• Passive immunization against SS
• Immunize another animal (rabbit, sheep, cow)
• Active immunization against SS
• Immunize animal of interest

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GH values over time in RBT
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RBT injected with SS-14 (5 ng/g BW)
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RBT passively immunized against SS-14 (125)