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(crit) 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.