We examined condition factor, hepatosomatic index and stomach fullness in brown trout to study if feeding intensity can be related to fish condition. Trout were collected at three locations during the summer in temperate rivers (Galicia, NW Spain). Our findings suggest that the feeding intensity is inversely related with the fish condition because the stomach fullness decreases with fish age and size and the condition factor is the lowest in young-of-the-year (YOY). In general, no significant differences among age classes were found in the hepatosomatic index, except in one river (the River Lengüelle) in which YOY shows the highest value. The high
feeding intensity of YOY during summer could be related with the increases in fish condition and survival in the later autumn and winter.
Knowledge of food resource partitioning between sympatric fish species is critical for understanding the fish communities functioning. Four sympatric fish species (Salmo trutta, Pseudochondrostoma duriense, Squalius carolitertii and Barbus bocagei) were captured in August 2010 in the River Tormes (Ávila, Central Spain) in order to study food resource partitioning between fish species such us as a possible mechanism enabling their coexistence, using a fuzzy principal component analysis (FPCA). Diet comparison among species shows that detritus are present in P. duriense, B. bocagei and S. carolitertii, although in different occurrence, showing that these species present typically omnivorous feeding habits. Regarding prevalent food, in all species, benthic prey constituted the most important prey in abundance terms, and terrestrial invertebrates were only consumed by S. trutta, S. carolitertii, and P. duriense. High overlap values (Schoener’s index from 0.8 up to 1) were found, but it may not indicate competition, since species can adopt different strategies to overcome competence. Thus, prey traits analyses suggest that differences in macrohabitat use, drift behaviour of prey and prey size are important adaptive features that may reduce the inter-specific competition in the fish community and permit the food partitioning that allows coexistence.