POPULATION AND GENDER-BASED DIFFERENCES IN TISSUE-SPECIFIC ENZYME-ACTIVITIES IN BRACKISH-WATER AND FRESH-WATER THREESPINE STICKLEBACKS, GASTEROSTEUS-ACULEATUS

Sticklebacks (Gasterosteus aculeatus) from a brackish water and a fres hwater population were compared immediately after removal from their h abitat and after being maintained in the laboratory. Glutamate dehydro genase activities in the liver and both lactate dehydrogenase and aspa rtate aminotransferase activities in the axial muscle were higher in t he brackish water sticklebacks than in the freshwater specimens. Liver glutamate dehydrogenase activities were higher in males than in femal es, whereas lactate dehydrogenase activities were distinctly higher in females. A significant positive correlation was found between size an d both aspartate aminotransferase and lactate dehydrogenase. The popul ation-specific activities of muscle enzymes are interpreted as an exam ple of evolutionary adaptation of enzyme regulation.