Reproduction in Fishes

Reproduction What defines “male” vs. “female”? Sexual strategies: Females must be “careful” in mate selection due to cost Male investments in reproduction : advertisement, colors, tubercles, kypes, displays, nest building, territorial defense, parental care, brood guarding

Anatomy Hagfish, lamprey: single gonads no ducts; release gametes into body cavity

Anatomy Hagfish, lamprey: single gonads no ducts; release gametes into body cavity Sharks: paired gonads internal fertilization sperm emitted through cloaca, along grooves in claspers

Anatomy Hagfish, lamprey: single gonads no ducts; release gametes into body cavity Sharks: paired gonads internal fertilization sperm emitted through cloaca, along grooves in claspers Chimaeras, bony fishes: paired gonads external and internal fertilization sperm released through separate opening

Anatomy Hagfish, lamprey: single gonads no ducts; release gametes into body cavity Sharks: paired gonads internal fertilization sperm emitted through cloaca, along grooves in claspers Chimaeras, bony fishes: paired gonads external and internal fertilization sperm released through separate opening Most teleosts: ova maintained in continuous sac from ovary to oviduct exceptions: Salmonidae, Anguillidae, Galaxidae, non- teleosts - these release eggs into body cavity when ripe

Anatomy In general: gametes produced only during spawning season gonads reduced during non-reproductive season

Timing and location of spawning Strategy: - avoid competition for spawning habitat - maximize access to food for offspring - minimize access to offspring by predators Example: Lake Champlain (New York/Quebec) anadromous – salmon catadromous – eels deep-water fall spawners – lake trout, whitefish medium depth spawners – smelt littoral spawners – sculpins, sunfishes stream spawners – suckers, darters, minnows pelagic eggs – burbot

Reproduction Bioenergetics: C = E + M + G + S + R C – consumption E – excretion M – metabolism G – growth S – storage R – reproduction

Reproduction Fecundity - egg size and number inversely related - egg number directly related to female size (within species) related to food supply, competition = population-regulating mechanism

Reproduction Fecundity Fractional spawners – produce eggs continuously, spawn frequently Batch spawners – single reproductive season release all eggs in a short period

Reproduction Onset of reproduction - males typically mature earlier and smaller than females - mature earlier if survival, growth are low - stable environment – delayed reproduction Survivorship - high if egg production is low, and vice versa - high-fecundity fish respond more rapidly to change

Reproduction Frequency of reproduction Semelparity - spawn and then die - huge investment in egg production Iteroparity - repeated reproduction - allows compensation for a “bad” year - more common in more unstable environments - may not spawn every year (sturgeon)

Reproductive strategies Fertilization - external except in livebearers (elasmobranchs, Poeciliidae) - mass spawning events (Clupeiformes, smelt) - several males to each female (Salmoniformes, lampreys) - several females to each male (Gobiidae) - single-pair matings (guppies)

Reproductive strategies Non-guarders - pelagic (broadcast) spawners - semi-buoyant eggs - high fecundity - egg and larval ‘migrations’

Reproductive strategies Non-guarders - pelagic (broadcast) spawners - benthic spawners - on coarse substrates (lake trout) - on vegetation (carp, perch) - on fine substrates (smelt)

Reproductive strategies Non-guarders - pelagic (broadcast) spawners - benthic spawners - brood hiders - build redd on coarse substrates (salmon, lamprey)

Reproductive strategies Non-guarders - pelagic (broadcast) spawners - benthic spawners - brood hiders - build redd on coarse substrates - beach spawners (grunion) - use another species (bitterling)

Reproductive strategies Guarders - choose substrate (largemouth bass)

Reproductive strategies Guarders - choose substrate (largemouth bass) - nest builders - rock and gravel (like a lentic redd - sunfishes) - plant material (sticklebacks) - holes, crevices, cavities (gobies, sculpin, blennies) - froth (bettas) - anemones (clown fish)

Reproductive strategies Bearers - carry eggs and/or fry with them - external bearers - transfer: Gasterosteidae, Sygnathidae (pipefishes, seahorses) - grade from attachment to skin, to open pouch, to closed pouch - gill chambers, forehead - mouth: males or females - some cichlids and bonytongues - obstetrical catfish carry eggs on ventral surface

Reproductive strategies Bearers - external bearers - internal bearers - facultative - killifishes - obligate (ovoviviparity) - Lake Baikal sculpins, - marine rockfishes (Scorpaenidae) - livebearers - Poeciliids, many sharks - gradient of nutrient supply - superfetation (multiple developmental stages present all at same time)

Reproductive strategies The other extreme: minimal male investment - Lophiiformes: deepsea anglerfishes - parasitic males

Alternative reproductive strategies Hermaphroditism - synchronous (or simultaneous) hermaphrodites Myctophiformes: (laternfishes) Atheriniformes: Aplocheilidae, Poeciliidae Perciformes: Serranidae (sea basses, hamlets) Labridae (wrasses), and others - "Egg-trading" in black hamlets Hypoplectrus nigricans (serranid)

Alternative reproductive strategies Hermaphroditism - consecutive (sequential) hermaphrodites first male (protandrous) – less common Stomiiformes (lightfish, dragonfish) Scorpaeniformes: Platycephalidae Perciformes: Serranidae, Labridae, and others Bluntnose minnow

Alternative reproductive strategies Hermaphroditism - consecutive (sequential) hermaphrodites first female (protogynous) Synbranchiformes (swamp eels – only freshwater example) Perciformes: Serranidae, Maenidae, Labridae - from 100% female to 100% male - from 100% female to 50%/50% male/female - some do not pass through a female stage ("primary males")

Alternative reproductive strategies Unisexual species Processes of DNA reassortment: 1. crossing-over during first meiotic division 2. random segregation of chromosomes in second meiotic division 3. addition of male and female chromosomes after fertilization

Alternative reproductive strategies Parthenogenesis: - females produce diploid eggs, no sperm used premeiotic endomitosis - mitotic division without cytokinesis Gynogenesis: - females produce diploid eggs, use sperm to stimulate development male genome not used congeneric species are used for sperm Hybridogenesis: one genome from female in egg, male genome discarded - then uses sperm to restore ploidy - no crossing over example: Poeciliopsis monacha-lucida

Alternative reproductive strategies Alternative male strategies - jacks (salmon and trout) - sneakers in bluegills, wrasses, other sunfishes - evolutionarily stable strategy - if small, become sneaker, avoid stress of being parental male - satellite males (mimic females) in bluegills, hover near nest

DEVELOPMENT

Developmental stages egg <0.5 mm - 10 cm - variable shape, attachments - variable buoyancy - water hardening yellow perch egg mass round goby (0.5 mm) lake trout (5 mm) skate (5 cm)

Developmental stages egg embryo - dependent on mother or yolk sac for food (free embryo)

Developmental stages egg embryo - dependent on mother or yolk sac for food (free embryo) larvae - not fully functional, may look totally unlike adult stage ends when axial skeleton is formed

Developmental stages egg embryo - dependent on mother or yolk sac for food (free embryo) larvae - not fully functional, may look totally unlike adult ends when axial skeleton is formed juvenile - small functional individual, immature adult - reproductively mature Credit: USFWS, GLFC

Indirect development (perch) - larval stages go through trophic phases different from adults Intermediate (salmonids) - embryonic stage with yolk; virtually no larval stage Direct development (gobies) - juvenile is fully functional miniature of adults (no larval stage)