METABOLIC SPECIALIZATION OF MUSCLE DURING DEVELOPMENT IN COLD-WATER AND WARMWATER FISH SPECIES EXPOSED TO DIFFERENT THERMAL CONDITIONS

Temperature and developmentally induced changes in indicators of muscl e growth and metabolic capacity were investigated in a cold-water and a warmwater fish species. Tilapia (Oreochromis mossambicus) larvae tha t were reared at 20, 25, and 30 degrees C up to 4 weeks after first fe eding, grew little until the 2nd week after first feeding. Subsequentl y, the fish reared at 25 and 30 degrees C exhibited increased growth r ates. Atlantic salmon (Salmo salar) that were reared at ambient temper ature (4.3 degrees C up to hatching, 9.7 degrees C from hatching to fi rst feeding, and 10.6 degrees C to 3 weeks after first feeding) grew f aster than salmon reared at 11 degrees C. In both species, carcass cyt ochrome c oxidase (CCO) activity increased rapidly with development or growth. In salmon, lactate dehydrogenase (LDH) activity increased wit h development whereas in tilapia it decreased. In the white muscle of tilapia and the red muscle of salmon, the density of mitochondria incr eased with development. Myofibre size increased with growth in tilapia irrespective of temperature but the number of myofibres increased onl y at 25 and 30 degrees C. At the low temperature for tilapia fry (20 d egrees C) and at ambient temperature for salmon larvae, CCO activity a nd red muscle mitochondrial density was not higher than in fish reared at increased temperature.