Effects of Starvation on Rainbow Trout Muscle

Abstract

This study deals with the effects of up to three months starvation on white and red muscle in mature and immature rainbow trout. Examined in the study were the histochemistry of the muscle, the dynamics of muscle fiber growth, key enzymes involved in energy metabolism and the chemical composition. Muscle fibers in the different muscle tissues did not respond to starvation in a consistent way. In red muscle starvation induced a narrowing of the range of fiber sizes, regardless of the stage of maturation of the fish. In white muscle of immature fish starvation for 3 months had no effect on fiber sizes whereas in sexually mature fish the fiber cross section areas were smaller than expected based on the weight of the fish. This was probably caused by a pronounced break down of muscle protein in mature fish for gonad formation and energy production without a simultaneous replacement of protein by water. Pink muscle in immature fish showed a response intermediate between red and white muscle. Starvation caused a decrease in the activities of certain enzymes in the energy metabolism of immature fish. Thus the glycolytic activity in white muscle was reduced by 70% after three months of starvation. In red muscle, oxidative capacity and fatty acid oxidation decreased during the early part of the starvation period but was partly restored in spite of prolonged starvation. These effects were much less pronounced in mature fish. The relative content of fat, glycogen and protein in the muscle showed no drastic response to starvation, with the exception of fat content in red muscle, which increased slower in starved than in fed fish. Significant differences as to occurrence of neutral fat, glycogen and oxidative capacity as well as fiber size pattern were demonstrated along the vertical axis of the epaxial white muscle.