Sex‐change linked growth acceleration in a coral‐reef fish, Thalassoma duperrey

Abstract

AbstractEnvironmental factors are known to affect the growth rates of fishes through most of their adult life. In the hermaphroditic saddleback wrasse (Thalassoma duperrey), the effects of social factors on growth were studied experimentally by subjecting individuals in submerged enclosures to various social environments that induce sex change. The results showed that social factors may either stimulate or inhibit the growth of adult fish. Individuals with one or more pen mates grew better than isolated individuals. Conspecifics stimulated more growth than heterospecifics. In paired fish, larger individuals inhibited the growth of smaller individuals. Growth rates were independent of both the sex and color phase of associates. Placing a tactile barrier between fish did not alter growth rates, but a tactile—visual barrier did. Increasing the space available to a fish did not increase the growth rate. Dominance relationships based on relative size and visual stimuli best explain the results obtained. Since all fish that showed growth acceleration also changed sex, a unitary, hypothalamically mediated, causal system is suggested. From an evolutionary perspective, sex‐change linked growth acceleration may reduce the cost of changing sex by shortening the nonreproductive interim in species in which males must be large to compete successfully for multiple matings.