MFWB_A - Fish Reproduction

anadromous

migrate from freshwater to marine to feed, return to freshwater to spawn

why do salmonids go to marine environments when most don’t have an obligate marine phase

produce healthier, larger offspring

investment of resident vs migrating salmonids

migrating - heavy investment but most do not live long enough for another spawning season, resident - less investment but live longer

multiple-sea winter fish

from populations where freshwater phase is longer, able to expend more energy at reproduction, generally larger

Atlantic salmon

spawn upstream in natal rivers in redds, external fertilisation, precocious male

precocious males

sexually mature parr that unknowingly fertilise around 40-50% of gametes, decrease reproductive of males, can get eaten if spotted

how can impact of precocious males be assessed

genotype most/all adults, molecule makers that rapidly evolve, allow for fine-scale comparisons and pedigree construction, microsatellites

fishery induced evolution

increases mortality in fish with higher age classes eg solea solea can live up to 40, in North Sea they barely reach 6

why do fish mature earlier in fisheries

plasticity, evolution

plasticity in fisheries

phenotypically plastic response to reduction in stock size induced by exploitation, relaxation of resource competition and fishing - compensatory growth

evolution in fisheries

removal of old spawners (larger) therefore no longer advantage for egg size and offspring survival, favour early-maturers, require generations of decreased fishing pressure to reverse

reaction norm

pattern of phenotypic expression of single genotype across range of environments

hermaphroditism in teleosts

sequential, simultaneous

sequential hermaphroditism

size advantage, protandry - male to female, worth becoming female at certain size, e.g, clown fish - all born male, largest becomes dominant female (brain changes first, then gonads), protogyny - female to male, defend better at certain size, e.g, territorial wrasse species

simultaneous hermaphroditism

low density model, primarily deep sea, e.g, hagfish, bathypterious species, contain both male and female reproductive parts

anthropogenic gender modification

EDC disrupt mostly freshwater fish, making them unable to lay eggs, decrease fertility of males, feminisation of male gonads, testis contain different variations of primary oocytes and degenerating ones, and spermatozoa

impact of feminisation on population structure

fewer breeding males depresses effective population size and decrease genetic diversity, e.g, roach - removal of older males may promote diversity