Diel patterns in the feeding and habitat use of O-group fishes in a regulated river: the River Great Ouse, England

Feeding and habitat use behaviour of juvenile O+ fishes, principally Rutilus rutilus (L.) and Leuciscus cephalus (L.) was analysed at 4-h intervals for a period of 24 h on 29 June, 27 July, and 13 September 1994 at a regulated site on the River Great Ouse, UK. Twenty-five random point samples were taken by electrofishing during each sampling period from a 250 m reach of the river. Catch per unit effort decreased at night for both R. rutilus and L. cephalus. The number of prey items in the gut and the number of taxa found also decreased at night except for R. rutilus on one occassion. Habitat use remained near constant, with only slight increases in depth and distance from the bank at night. Use of Nuphar lutea by roach increased at night. Chub tended to avoid Nuphar lutea and were positively associated with emergent macrophyte and algal cover both during the day and night.