Seasonal variations in the physiological status and energy content of somatic and reproductive tissues of chub

The seasonal fluctuations in condition, nutrition and somatic energy content, and gonad development cycle were investigated in chub Leuciscus pyrenaicus from the headwaters of the Guadalete River, a freshwater ecosystem characterized by strong seasonal fluctuations in discharge and water level, temperature and food supply. The relationship between somatic stage and gonad cycle was also investigated and discussed. Condition, nutrition and somatic energy cycles could be divided into two distinct periods: from April to January with summer decreases and autumn increments, which is common for juveniles and mature fish; and from January to March, when juveniles and mature fish displayed different temporal variations related to the reproductive cycle. Gonad development took place from the end of the winter into the summer, the testes developing before the ovaries. Spawning started in late spring (May) and continued into summer (June and July), with fish quiescent by autumn (September). The results suggest that, for L. pyrenaicus , both environmental factors (e.g. food supply, water temperature) and reproduction needs affect the condition, nutrition and somatic energy storage of fish, which have been used as indicators of the physiological status of the population.