LIFE-HISTORY PATTERNS OF THE COMMON CARP, CYPRINUS-CARPIO, IN THE ESTUARY OF THE GUADALQUIVIR RIVER IN SOUTH-WEST SPAIN

We examined 1567 carp caught in rice field drainage canals in the estuary of the Guadalquivir river (37-degrees-N, 6-degrees-25' W). The stock was comprised of a small number of age groups, among which 0 + and 1 + were dominant. Growth was divided in four periods: rapid (June-July); slow (August-November), no growth (December-March), and resumed growth in April when an annulus was formed. A classification based on 12 wild carp populations revealed that growth depends on latitude, and that growth of the studied stock was mediocre, probably due to high salinity. A decrease in somatic condition coincided with an increase in gonadosomatic index (GSI). Specimens of the same stock, age and/or length showed considerable difference in development of the gonads. Gonadal activity began in September and by late Autumn some gonads had reached up to 20% of body weight. The situation remained static during Winter till April, when most reproduction occurred. Later, GSI values decreased to reach a minimum in September. Maximum average GSI values in females were twice those in males. Both sexes achieved maturity during the third growing season (2 + age-group) at a minimum fork length (F.L.) of 110 mm. Fecundity, before reproduction, was expressed by Fec = 241.701 F.L. (mm) - 26776.2. The sex ratio did not differ significantly from 1:1.