Fish Behavior and Reproduction

Migration

• Anadromous—spend most of life in sea, then migrate to freshwater to breed

  • Chinook salmon, striped bass, lamprey

  • Must have adaptation to prevent diffusion of water into the body

• Catadromous—freshwater fishes, travel to spawn in sea

  • Americal eel

  • Must have adaptation to prevent water loss

• Diadromous—move between freshwater and sea, regardless of breeding

  • Bull shark

Timing of reproduction

• Depending on species, can be influenced by temperature, day length, pH

• Some species spawn once they die—Chinook salmon

• Some species reproduce multiple times over several year—bass

• Age of sexual maturity varies

  • Adult survival high = later sexual maturity

  • Growing population = earlier sexual maturity

Sexual dimorphism

• Differences in form or color between the sexes

  • size differences

    • Adult females often larger than adult males

    • Males larger when they compete for females

  • Males may become brightly colored during breeding season

    • Guppy

    • Stickleback

  • Tubercles on head of males

    • bluehead chub

  • Anglerfish—parasitic male

Bonding

• Most do not have a long-lasting pair bond

• Most teleost females deposit eggs into water, sperm are then deposited by males

  • Oviparous—young develop outside mother’s body. 2 days—several months

  • One female may mate with many males

• Most Chondrichthyes have internal fertilization

  • Viviparous—young develop within mother’s body. 6-22 months

  • Modified pelvic fins—claspers—insert into female and transport sperm

Protection of developing young

• Some hide eggs or build nests

  • Trout and salmon

• Internal development until live birth in some

  • sharks

• Maternal mouthbrooding—females take eggs in mouth and inhale sperm

  • sea catfishes

• Brood pouch

  • male seahorse

Sex change in fish

• Synchronous hermaphrodites—both male and female organs at same time

• Sequential hermaphrodites

  • change sex over time

    • Protogyny: females turn into males

    • Protandry: males change into females

• Continuing research is finding sex change is more common than previously thought

Growth and Development

• Oviparous fish

  • Embryonic: in egg

  • Larval: catches food, body develops

  • Juvenile: growing, nonbreeding

  • Adult: able to spawn

• Viviparous fish

  • born as miniature adults

Longest-lived fish: Lake Sturgeon