Some aspects of the biology of Micropterus salmoides such as growth, population structure and reproduction, were studied in the Primera de Palos’ lake. A total of 200 specimens were captured (98 females, 86 males and 16 juveniles) and distributed into seven different age-classes (from 0+ to 6+). Specimens 6+ were exclusively females. The mean values of male length and weight were slightly higher than females ones but the differences were not significant between sexes. The parameters of the von Bertalanffy growth’s curve were L∞=503.6 mm, k=0.19, t0=-1.04 for males and L∞=512.6, k=0.18, t0=-1.05 for females. The final values of the Gompertz growth’s curve for weight were: W0=36.35, G=10.61, g=0.06 for males and W0=31.81, G=6.93, g=0.11 for females. Reproduction took place in spring. Females mature older than males, in age-class 2+. The results clearly indicate that the largemouth bass population has acclimatised well to the Primera de Palos’ lake, having found environmental and trophic conditions that are favourable to its development.
The Joaquín Costa reservoir contains a mixed fish assemblage of native and exotic species. Feeding habits and feeding relationships of species in the fish assemblage were analysed over a one year cycle. Differences in diet composition were found both between species and within species among seasons. Food overlap and trophic similarity among species also showed seasonal variations. Cluster analysis differentiated four groups of predominant diet: (1) macroinvertebrates (trout and largemouth bass), (2) detritus (nase), (3) cladoceran crustaceans and (4) an omnivorous feeding regime, with large seasonal variations in food habits. Food of fish species included in groups 3 and 4 (roach, white bream, barbel, common and mirror carp) varied seasonally. Using graphical models of feeding strategies, similarity indexes, cluster and multivariate analyses based on the relative importance of food categories in the diet of the species, we illustrate that the fish assemblage showed food resource partitioning according to food habits and foraging habitats within the reservoir.