Interactions between individual feeding behaviour, growth, and swimming performance in juvenile rainbow trout (Oncorhynchus mykiss) fed different rations

Aerobic swimming performance (critical swimming speed, U-crit), food consumption per meal (by X-ray radiography), specific growth rate (SGR), haematocrit, and fin condition were monitored in individual juvenile rainbow trout (Oncorhynchus mykiss). The fish were held in groups over a 9-week period and fed daily group rations (dry food) of 2.0, 1.5, 1.0, and 0.5% wet body mass (BM). day(-1). SGR declined and competition increased at lower ration levels, as reflected by greater fin damage, reduced haematocrits and condition factors, and, at 0.5% BM . day(-1), a substantial increase in the coefficient of variation among individual meals. Absolute U-crit, also declined at lower ration levels. However, there was no relationship between U-crit and haematocrit, fin damage, or condition factor in any of the ration groups. A negative correlation was found between U(cri)t and SGR in individual trout fed a group ration of 2.0% BM . day(-1), but a positive correlation was seen at 0.5% BM . day(-1) and no relationship at 1.0 and 1.5% BM . day(-1). There was a positive relationship between individual SGR and food consumption only among fish fed a ration of 2.0% BM . day(-1). A significant negative relationship between U-crit and individual food consumption was also found among fish in this ration group.