SEASONAL-VARIATIONS IN THE PHYSIOLOGICAL STATUS AND ENERGY CONTENT OFSOMATIC AND REPRODUCTIVE TISSUES OF CHUB

The seasonal fluctuations in condition, nutrition and somatic energy c ontent, and gonad development cycle were investigated in chub Leuciscu s pyrenaicus from the headwaters of the Guadalete River, a freshwater ecosystem characterized by strong seasonal fluctuations in discharge a nd water level, temperature and food supply. The relationship between somatic stage and gonad cycle was also investigated and discussed. Con dition, nutrition and somatic energy cycles could be divided into two distinct periods: from April to January with summer decreases and autu mn 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 developme nt took place from the end of the winter into the summer, the testes d eveloping before the ovaries. Spawning started in late spring (May) an d continued into summer (June and July), with fish quiescent by autumn (September). The results suggest that, for L. pyrenaicus, both enviro nmental factors (e.g. food supply, water temperature) and reproduction needs affect the condition, nutrition and somatic energy storage of f ish, which have been used as indicators of the physiological status of the population. (C) 1997 The Fisheries Society of the British Isles.