Stunted Versus Normally Growing Fish: Adapted to Different Niches

Fishes have flexible and indeterminate growth, and many of them do not reach their growth and size potential. They may become stunted with impaired growth and early maturity as a phenotypically plastic reaction. Chief causes of stunted growth are negatively density-dependent food availability and keen intraspecific competition leading to environmental stress. Typically, their growth levels off early in life as the energy consumption approaches the energy costs of maintenance. Females appear to attain maturity soon after the energy surplus from feeding starts to decrease, males are often more variable in size at maturity owing to alternative mating strategies and their size at maturity depends on both species specific mating behaviours and environmental opportunities. In polyphenic/polymorphic populations, where the fish are split between stunted and large-growing individuals, stunted individuals do not perform a required ontogenetic niche shift needed to grow larger. The adult morphology of stunted fish typically appears to be similar to the morphology of the juveniles. Their secondary sexual characters are less well developed and phenotypically, they retain adaptation to their early feeding niche which is different from that of large growing individuals. There are open questions regarding to what extent genetics and epigenetics regulate the life histories of stunted phenotypes.