REPRODUCTION IN FISHES 1

Introduction Great diversity in reproduction patterns of fishes Many change gender Some mate for life while others are promiscuous Different strategies have developed in order to reach a common goal - to have the greatest number of young survive to reproduce The larger the individual the more gametes produced 2 Odyssey Expeditions

Reproduction Modes Oviparity - external development – Lay undeveloped eggs – External fertilization (most all bony fishes) – Internal fertilization (some cartilaginous fishes) Ovoviviparity – internal development – No direct nourishment from mother (fert. eggs carried) – Advanced at birth (some cartilaginous fishes) – Larval birth (few bony fishes) Viviparity – internal development – Direct maternal nourishment (placental) – Fully advanced at birth (adv. sharks and few bony fish) 3

Oviparity Most common Lower energy cost to produce eggs Survival is low, millions produced in hopes that at least one will survive to reproduce Larval fishes typically spend 14 – 30 days feeding among the plankton clouds. Juveniles typically settle in areas far from where they were spawned due to dispersal from the currents 4 Odyssey Expeditions

Ovoviviparous/Viviparous Eggs have lower rate of predation when carried in mother Much higher energy cost per egg Therefore fewer eggs produced Young born as miniature adults Young generally stay in the same area as mother 5 Odyssey Expeditions

Live-Bearers Very few bony fishes Typically cartilaginous fishes Viviparous and Ovoviviparous Fertilization internal Sperm transferred into cloaca (opening used for excretion and reproduction) by the males claspers (modified pelvic fin) 6 Internal fertilization

Breeding Chances Semelparous – spawn once then die – Ex. Lamprey, salmon Iteroparous – spawn more than once – most fishes 7 Semelparous salmon

Mating Systems Promiscuous – both sexes have multiple partners (mass spawning events, nassau grouper) Polygamous – one sex has multiple partners – Polygyny – males have multiple partners (most common) Harem formation – male has breeding right to group of females (wrasses) – Polyandry – females have multiple partners (uncommon) Monogamous – sexes have one partner (butterflyfishes, anglefishes) 8 Odyssey Expeditions Monogamous Polygyny Harem

Genders Gonochroistic – sex is fixed, one sex (most fishes) Hermaphroditic – contain both sex organs at some point – Simultaneous – both sexes at once (deep water fishes, hamlets) – Sequential – changes sex Protandrous – male into female (moray eels) Protogynous – female into male (most common) – wrasses, parrotfishes 9 Jon Buchheim