Seasonal, sexual and individual variations in gonad weight and secondary sexual characters of the dark chub, Zacco temmincki.

概要

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The relationships among body length, gonad and body weights and secondary sexual characters of the dark chub, <I>Zacco temmincki</I>, were analyzed with reference to their variations. Both condition factor and gonosomatic index (GSI) greatly increased in the pre-mating season. Body size was positively correlated with GSI value for females, except in post-spawning periods, but negatively correlated or uncorrelated for males. Individual variation (CV) of both condition factor and GSI value also increased in the pre-mating and mating seasons. Breeding color and pearl organs on the head developed in both sexes all the year round, and most conspicuously in males in the mating season. Pearl organs on the anal fin only developed in males in the mating season. The development of these secondary sexual characters neither necessarily indicated sexual maturation nor a high potential for reproduction, but was greatly associated with large body size. Breeding color was believed to function as a signal showing the development of pearl organs and body size, pearl organs on the head as a weapon in conspecific aggressive encounters and pearl organs on the anal fin as a tool for burying eggs in spawning behavior.
日本魚類学会の論文