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Fish Reproduction Brian Peterson, M.S. 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. 1999 Census Catches ~ $1 Billion in Sales.

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Fish Reproduction Brian Peterson, M.S.

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Fish ReproductionBrian Peterson, M.S.


  • 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

1999 Census Catches ~ $1 Billion in Sales

AquacropValue ($)


Trout 77,000,000


Ornamental 69,000,000

Source: Economic Research Service, USDA

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

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

Terms to Know

  • Teleost—Fish that exclude jawless fish, cartilaginous fish, lobe-finned fish, and sturgeon.

  • Vitellogenin—Glycolipoprotein produced in the liver and accumulated in the oocyte as yolk.

  • Vitellogenesis—Process of yolk formation.

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

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.

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.

Role of GTH-II and GnRH

  • GTH-II: stimulates events leading to final oocyte maturation and ovulation in females and spermiation in males.

  • GTH-II—stimulated 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.

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.

Changes in levels of GTH-I and GTH-II in coho salmon during reproductive maturation













Vitellogenesis Ovulation

Adapted from Dickoff and Swanson, 1990

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.

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.

A section through a cystovarian ovary showing ovigerous folds and location of oocytes

Adapted from Turner, 1983





Mesonephric Kidneys

Mesonephric Kidneys

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).

Diagrammatic representation of the follicle and oocyte during early vitellogenesis

Nagahama, 1983

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)

Oocyte Recruitment

Three modes of oocyte development in teleosts

  • Asynchronous- oocytes at all developmental stages are present in the ovary.

    Ex: Tropical fish

Mechanisms of Sex Determination

I. Recombination of sex chromosomes at fertilization

a. Chromosomal genotype

Mammals and most fish: Male= XY


Birds and some fish: Male=ZZ


Sex Determination/Development

b. H-Y Antigen

1. Male specific antigen present on the surfaces of cells

XY=H-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

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

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 genitalridge--Mechanism is unclear in fish

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

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

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 for~$10-20/lb

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.

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

Hermaphroditism in Fish

3. Synchronous hermaphroditism-Both male and female states coexist functionally

-Sea bass (self fertilization)

Research at University of Idaho


SS (-)

GHRH (+)

Anterior Pituitary


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

GH values over time in RBT

RBT injected with SS-14 (5 ng/g BW)

RBT passively immunized against SS-14 (1:25)

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