CHANGES IN ALKALINE-PHOSPHATASE ISOENZYME ACTIVITY IN TISSUES AND PLASMA OF ATLANTIC SALMON (SALMO-SALAR) BEFORE AND DURING SMOLTIFICATION AND GONADAL MATURATION

Changes in tissue and plasma isoenzymes of alkaline phosphatase (ALP) were qualitatively and quantitatively determined for male and female A tlantic salmon parr: silvery parr, smolt, immature grilse, prespawning grilse and postspawning grilse using cellulose acetate electrophoresi s, densitometry and spectrophotometry. Tissue ALP isoenzymes were isol ated from intestine, kidney, bone, liver, and gonad and compared to pl asma isoenzymes. Parr plasma displayed three isoenzymes from bone and liver (slow and fast). During smoltification, ALP activity increased i n tissue extracts from liver, gonad, and kidney of males and females. Total plasma ALP activity also increased and was due to slow and fast liver isoenzymes. During ovarian development, total ALP plasma activit y increased in females and was due mostly to liver isoenzymes and an i ncompletely identified isoenzyme or isoenzyme mixture (band 2). Howeve r, in males total ALP plasma activity did not increase during maturati on and no band 2 was evident. In male and female maturing adult grilse , bone ALP activity declined and the isoenzyme band evident in parr pl asma could not be detected. ALP activity declined in the plasma of pos tspawning males and females. In females this was due partly to the tot al clearance of band 2 from the plasma, together with lowered levels o f liver isoenzymes. Treatment of postspawned grilse in February and Ma rch with triiodothyronine and thyroxine elevated plasma thyroid hormon e levels and increased plasma ALP levels. In conclusion, plasma ALP is oenzyme activities change with physiological state, and knowledge of t he conditions governing these changes is important when using these en zymes as a diagnostic tool.