Feeding ecology of Leuciscus cephalus and Rutilus rubilio in southern Italy

The diet and feeding relationships of two cyprinids, the Italian orange-fin roach Rutilus rubilio and the chub Leuciscus cephalus, were studied in southern Italy by the analysis of 189 gut contents. Fish species were sampled in conditions of sympatry/hybridisation in the River Sinni, and allopatry in the River Mercure-Lao (roach) and in the River Raganello (chub). The diet of both fish species included both plant material and invertebrates. The broad spectrum of prey eaten showed that both fish species looked for invertebrates along the whole water column and particularly on the surface. For the River Sinni a high dietary overlap was found. The high contribution of plant material in the overall diet of roach in the presence of other cyprinids species, compared with the almost equal importance of plant material and animal food in allopatry, suggested that competition could be the cause of roach dietary shift towards suboptimal food sources. For the river Raganello, the high proportion of vegetation in the diet of chub, compared to the River Sinni, was explained as a consequence of habitat degradation caused by anthropogenic activities. Our results confirmed the generalist and opportunistic foraging behaviour of both fish species.