The adaptation of digestive enzymes to temperature, season and diet in roach, Rutilus rutilus L. and rudd Scardinius erythrophthalmus L. 1. Amylase

Seasonal changes of the amylolytic activity in the gut content of roach and rudd in four Tyrolean lakes and the adaptation of the amylase to four acclimation temperatures and to different natural foods were studied. In roach amylolytic activity varied with the environmental temperature. Between September and October, however, enzyme activity shifted to a higher level where it remained for the entire cold season. In rudd, which has almost the same seasonal pattern of amylolytic activity as the roach, the activity of the enzyme is independent of environmental temperature. This suggests an endogenous rhythm of enzyme activity. Under natural conditions the roach, but not the rudd, has a higher amylolytic activity when feeding on animals and a lower activity when feeding on detritus. The laboratory experiments revealed no significant differences in amylase activity between fish feeding on animals and those feeding on plants, although in both species the enzymatic activity was lowest when Chara served as food.