Growth dynamics of muscle fibres, dry weight, and condition in relation to somatic growth rate in yearling rainbow trout (Salmo gairdneri)

Abstract

Rainbow trout (15.5 cm) fed "ad lib." rations grew a little faster at 12 °C than at 16 °C, and both groups grew much faster than a third group at 12 °C receiving "3–4%" rations. Growth of the mosaic muscle mass was characterized by increase in fibre mean diameter, though most bulk increase (up to 25 cm or more) resulted from increase in fibre number. Fibre diameter: fish length was least in the fastest growing trout (12 °C ad lib.), signifying their greater ability to add new fibres during growth compared with the slower growing trout; diameter range increased markedly among trout > 18 cm long, but small fibres (< 20 μm) persisted in diminishing numbers even in the largest trout. In the 12 °C ad lib. trout, condition (K) correlated with length and fibre diameter; in the slower growing groups K was more influenced by mean fibre diameter. A higher asymptote of K occurred at greater length in the fastest growing group than in the two slower growing groups. Percent dry weight: length was greater for 16 °C ad lib. than for the fastest or slowest growth groups; absolute dry weight: length ratios were similar for 12 °C and 16 °C ad lib. trout; both exceeded those for the 12 °C 3-4% group.