AGE STRUCTURE, GROWTH AND REPRODUCTION OF RUTILUS-LEMMINGII IN AN INTERMITTENT-STREAM OF THE GUADALQUIVIR RIVER BASIN, SOUTHERN SPAIN

The age, growth and reproduction of Rutilus lemmingii (Steindachner, 1 866), an endemic cyprinid from the Iberian Peninsula, was studied for over a period of two years in a small seasonal tributary of the Guadal quivir river basin. Approximately 65% of the total growth in length oc cured in the first year of life. Males reached a maximum age of 3+ yr (Fork Length, F.L. = 114 mm) and females 4+ yr (F.L. = 144 mm). Both s exes matured during their second year of life (1+). The overall sex ra tio (334 males to 389 females) differed significantly from unity. Soma tic condition decreased markedly during the reproductive period of Mar ch to May. R. lemmingii is a multiple spawner and releases two batches of eggs per female each year. Mean egg diameter of the first batch wa s larger than the second one. The regression between fecundity and For k Length (mm) was: Fec = 0.014 F.L.(2.858). Compared with available in formation, this R, lemmingii population, located at a lower latitude, is characterized by fast growth, early maturity, high level of reprodu ctive effort, and a short life-span. These life-history characteristic es are typical of species in unstable environments, where adult mortal ity is high, variable or unpredictable.