Feed efficiency of Rainbow trout (Onchorynchus mykiss) kept at high and low stocking density

Abstract

Feed efficiency is a trait of high economic importance in fish production, and is highly related to feedingregimes employed and stocking density. However, feed efficiency is difficult to estimate because measurementsof individual feed intake are generally not available in fish that are usually reared in groups intanks. An alternative is to estimate feed efficiency using tank as the unit of measurement. The objectiveof this study was to investigate tank residual feed intake in rainbow trout kept at high (HD) and low (LD)stocking density during 42 days (Day 0-14 and Day 14-42) and the consequences of subsequently reducingdensity in the HD treatment between 42 and 78 days (Day 42-61 and Day 61-78). HD fish weighedless at all times than LD fish (P < 0:05). LD fish grew faster than HD fish (P < 0:05) but not betweenDay 42-61. The coefficient of variation of body weight was larger in HD fish than in LD fish (P < 0:05)at Day 14 and Day 42. LD fish ate more than HD fish between Day 14-78 (P < 0:01). HD fish were lessfood efficient than LD fish between Day 0-14 but more food efficient between Day 42-61. A higher coefficientof variation of body weight in the HD tanks suggests that growth and feed intake were inhibitedbecause of dominance relationships at a high stocking density and possibly competition for food. Afterrelocating HD fish to a low density treatment, HD fish showed compensatory growth and compensatoryfeed efficiency. Although it is not practical to estimate residual feed intake individually in fish, this researchshows that calculation of tank residual feed intake can be used as an alternative, especially whenused to compare families for family trait selection.