PRELIMINARY INSIGHT INTO AGE AND GROWTH OF THE IBERIAN CHUB (LEUCISCUS-PYRENAICUS) IN THE SORRAIA SYSTEM

An investigation of age and growth in the Iberian chub Leuciscus pyren aicus Gunther, 1868 revealed a seasonal growth pattern, with annulus f ormation restricted to a short period of the year (May/June). Maximum ages were 6+ for both sexes. During and after the third year females g rew at faster rates than males, and the most important decrease in gro wth rates occurred between age II and III in males and between age III and IV in females. Mean back-calculated standard lengths of III and I V age classes were significantly higher in the River Sorraia. Mean wei ghts of I and II age classes were higher in Sor stream whereas the ind ividuals from III ad IV age classes were heavier in the River Sorraia. Shifts in growth rates are discussed in relation to seasonal and spat ial variations in the environmental conditions as well all to sexual m aturity.