Early starvation limits survival in amphidromous fishes

Abstract

Newly hatched amphidromous larvae drift downstream to the sea. Since there is practically no food available for drifting larvae, an extended downstream migration may enhance the risk of starvation. We hypothesized that early survival of amphidromous fish varies among populations according to the length of the river, due to its effect on larval starvation. The hypothesis was tested with the common Japanese amphidromous goby, Rhinogobius brunneus . Based on morphological characteristics, larvae were categorized as being in an endogenous feeding state (EFS) or irrecoverable starved state (ISS). The frequency of ISS larvae in the population from a long river was nearly twice the frequency in the population from a short stream. More than half of larvae were judged to be dying during downstream migration in the comparatively long river, although this was possibly an underestimation. It is suggested that early starvation limits reproductive success far from the sea.