Effects of varying rearing temperatures on expression of different trypsinisozymes, feed conversion efficiency and growth in Atlantic salmon (Salmo salar L.)

Hatching and start-feeding temperatures affected the expression of differen t trypsin isozymes in the pyloric caeca of Atlantic salmon. Hatching temper ature of 10 degrees C induced the expression of the common isozyme TRP-2*10 0, and of 6 degrees C induced the variant TRP-2*92 (p<0.01). In contrast, s tart-feeding temperature of 12 degrees C significantly (p<0.0001) influence d the expression of the variant TRP-2*92, compared to 6 degrees C. The freq uencies between different trypsin isozyme patterns were not changed at late r stages under varied rearing temperatures. The frequency distribution between Atlantic salmon without and with trypsin variants was about 0.4:0.6. The trypsin isozyme TRP-2*92 was the major var iant in Norwegian salmon, while the trypsin variant TRP-1*91 was dominant i n Scottish salmon, at frequencies of 0.47 and 0.42, respectively. The prese nce of both the common and either variant trypsin isozymes were important f or feed utilization and growth at varying rearing temperatures. Trypsin iso zymes are functionally sensitive to different temperatures. The expression of the common trypsin isozyme TRP-2*100 is important when the water tempera ture is > 8 degrees C, while it is important for the expression of the vari ant TRP-2*92 when the water temperature is less than or equal to 8 degrees C, especially below 6 degrees C. The variant TRP-1*91 was observed to perfo rm effectively at a wider temperature range than the variant TRP-2*92, but not at temperature less than or equal to 6 degrees C. Genetic variation in trypsin isozyme pattern is a primary factor affecting food conversion efficiency and growth under different rearing temperatures.