Scaling effects on hypoxia tolerance in the Amazon fish Astronotus ocellatus (Perciformes : Cichlidae): contribution of tissue enzyme levels

Astronotus ocellatus is one of the most hypoxia tolerant fish of the Amazon ; adult animals can tolerate up to 6 h of anoxia at 28 degrees C. Changes i n energy metabolism during growth have been reported in many fish species a nd may reflect the way organisms deal with environmental constraints. We ha ve analyzed enzyme levels (lactate dehydrogenase, LDH: EC 1.1.1.27. and mal ate dehydrogenase, MDH: EC 1.1.1.37) in four different tissues (white muscl e, heart, liver, and brain) from different-sized animals. Both enzymes corr elate with body size, increasing the anaerobic potential positively with gr owth. To our knowledge. this is the first description of scaling effects on hypoxia tolerance and it is interesting to explore the fact that hypoxia s urvivorship increases due to combining effects of suppressing metabolic rat es and increasing anaerobic power as fish grow. (C) 2000 Elsevier Science I nc. All rights reserved.