Feeding behaviour and protein turnover in fish
Feeding behaviour and growth of rainbow trout, Oncorhynchus mykiss (Walbaum), were found to be influenced by the position of an individual in the group feeding hierarchy. Dominant animals, consuming a greater proportion of the group meal, showed less day-to-day variation in consumption and higher growth rates compared to subordinates. The relationship between consumption, growth and protein synthesis and the influence of protein turnover on individual differences in growth efficiency in rainbow trout were examined. Rates of protein growth and synthesis increased significantly with increasing protein consumption. However, considerable inter-individual variation was found and fish with similar consumption rates showed variation in protein growth rates of up to 1% .d-1. Growth efficiency was related to differences in protein turnover with more efficient fish having reduced rates of protein degradation. The effect of dietary protein quality on consumption, growth and protein turnover in sea bass, Dicentrarchus labrax (L.) was studied using a fish meal diet (FM) and a fish meal/greaves meal diet (GM). Whole-body growth rates and rates of white muscle protein synthesis and growth were similar between the two groups. Whole-body and white muscle rates of protein synthesis rates were similar in both groups over 24 hours following a single meal. However, white muscle free amino acid levels were 50% lower in the GM group. The similarity in rates of protein synthesis was attributed to the rate-limiting free pool concentration of tryptophan in both diet groups. The effect of temperature on rates of protein growth and synthesis was examined using rainbow trout fry. As water temperature was increased (from 5°C to 15°C) higher rates of protein growth were brought about by an increase in the rate of protein synthesis due to increased RNA activity and reduced protein turnover.