Comparison of response distance to prey via the lateral line in the ruffe and yellow perch

The ruffe Gymnocephalus cernuus and the yellow perch Perca flavescens (both Percidae), have very different cephalic lateral line systems. The ruffe, which is nocturnal and frequents turbid water, has a cephalic lateral line with very wide canals, large neuromasts, and membranes covering the canal openings. This anatomy is convergent with that of many deep-sea fishes. The yellow perch has a lateral line composed of neuromasts enclosed in narrow canals freely open to the water. This anatomy is typical of active, diurnal, shallow-water fishes. Laboratory experiments in the dark using infra-red video equipment revealed that the ruffe detects Daphnia magna (Crustacea: Daphnidae) and the mayfly Hexagenia limbata (Insecta: Ephemeridae) at a greater distance than the yellow perch and that it also swims faster whilst searching for prey. The swimming of the ruffe consists of a thrust by the pectoral and caudal fins, followed by a glide, the prey being detected during the glide. It is suggested that the membranes over the openings in the ruffe's lateral line function to eliminate self-generated laminar flow 'noise' from reaching the neuromasts.