Reproduction and ontogeny
  1. Reproductive Anatomy
    1. Gonads:
      1. Composite organs, comprised of
        1. germ cells and gametes
          1. gametes start as primordial germ cells
          2. sperm: spermatogonia, other intermed stages, producing 4 spermatozoa
          3. eggs: oogonia, becomes surrounded by follicle, invested with yolk, then ovulation, freed from follicle, and hydration. One egg produced per oogonium.
        2. somatic cells: nourish, physically support, regulate development of germ cells
        3. gonoducts
      2. Agnatha
        1. sperm and eggs shed into body cavity, expelled through pores
        2. single gonad
      3. Chondrichthyans (24-2, p 399 bond)
        1. Testes and ovaries paired but asymmetric, right bigger than left
        2. males:
          1. sperm shed into duct shared with kidney,
          2. Leydigs gland makes seminal fluid
          3. pass out of body through claspers
        3. females
          1. eggs shed into coelom, go into funnel at head of oviduct.
          2. fertilization, then shell added to egg
          3. retention of young in uterus, or egg laying
      4. Osteichthyans (26-1, p 454 bond)
        1. testes
          1. primitive bony fishes: testis associated with kidney
          2. teleosts: duct from testes opens to outside ant to urinary pore
        2. ovaries
          1. lower bony fish: ovaries open into body cavity and eggs conveyed through funnel into oviduct
          2. teleosts: oviducts continuous with ovary covering
          3. many modifications associated with internal brooding of young
        3. usually paired, sometimes degree of fusion.
    2. External differences
      1. usually very hard to tell male from female
      2. sex may be indicated by color (for courtship, territoriality), structures that function in mating (breeding tubercles) or sperm delivery (intromittent organs)
  2. Reproductive Physiology
    1. Hormones (schematic in Bond, illustration of gland in Evans)
      1. Hypothalamus (=neurohypophysis) at base of brain, with neurons: these release gonadotropin releasing hormone (GtRh), supplied to adenohypophysis via portal system, or direct neural control of adenohypophysis. May be multiple forms of GtRH
      2. adenohypophysis releases gonadotropins
      3. these stimulate gonadal development and secretion of steroids in gonads
      4. Steroids (e.g. testosterone and derivatives; progesterone) have diverse effects, act on many target tissues
    2. Differentiation
      1. interaction between genetic and environmental factors
      2. sex steroids induce differentiation; source of these steroids before gonads have matured unknown
      3. complexities
        1. temperature-dependent sex determination
        2. hermaphroditism
    3. Maturation and reproductive timing
      1. important environmental cues
        1. photoperiod
        2. temperature
        3. tidal and lunar cycles
        4. spawning substrate
        5. mate availability, courtship
  3. Fertilization
    1. Sperm
      1. activated (become mobile) once enter aquatic envt or female
      2. longevity variable, usually quite short
    2. Egg
      1. protected by egg case or tough chorion
      2. most eggs basically spherical, can be ovoid
      3. pelagic eggs usually about 1 mm in diameter
      4. demersally spawned eggs bigger
      5. live-bearers: may start with very small eggs and no yolk, or big eggs with yolk
      6. Micropyle: a pore in the egg envelope that admits sperm, access to egg membrane. Probably releases substances guiding sperm
      7. After one sperm has penetrated, others blocked
      8. Egg has yolk and oil globules to nourish developing embryo
      9. Other distinctive characters: filaments, number of oil globules, pigment
  4. Development
    1. In the egg
      1. Standard vertebrate cleavage
    2. Hatching
      1. softening of chorion: enzymes secreted by mouth or head of embryo
      2. How long?
        1. temperature dependence
        2. diapause of some species
        3. hatching can be triggered by external events, e.g. flooding of intertidal eggs in Fundulus
        4. Short incubation of eggs: tropical reef fish, ca 12 hours
        5. Long incubation: trout and salmon, up to 6 months in gravel; egg cases of elasmobranchs
    3. Developmental scheme (fig. 9.1, Helfman et al.)
      1. After hatching, there is often a yolk-sac stage: a larva that hasn't begun independent feeding

        2. the transition to feeding is highly vulnerable stage: food must be abundant, conditions must be right for development of successful predatory behavior

      2. the flexion of the notochord is a significant developmental step; fin rays begin to form, swimming capabilities developing
      3. the next major step is metamorphosis,
        1. larva loses larval characters, gain juv/adult characters
        2. transition to juvenile/adult habitat, change in lifestyle
        3. vulnerable stage also
        4. metamorphosis can be dramatic: e.g. flatfish
      4. many variations on this scheme. In many fish, development is 'direct', no larval stage once hatched
    4. Larval morphology
      1. Larvae have unique morphology; specializations for different habitat than adult stage
      2. larvae typically transparent, with pigment spots (melanophores)
      3. shape: variable, helps in family level identification
      4. spines on head: anti-predation
      5. modifications of fins: heavy spines, trailing filaments (mimics of siphonophores?)
      6. gut: may be long and trailing
      7. eyes: may be odd shapes, or on stalks.