HYPERPLASIA OF THE ADRENAL CORTICAL TISSUE IN PACIFIC SALMON (GENUS ONCORHYNCHUS) AND RAINBOW TROUT (SALMO GAIRDNERII) ACCOMPANYING SEXUAL MATURATION AND SPAWNING

Abstract

A comparative study was made of the histological changes occurring in the adrenal cortical tissue of the Pacific salmon, the sea-run steelhead trout, and the non-migratory rainbow trout at various stages in their life cycles with the purpose of ascertaining whether there exists a relationship between degree of adrenal hyperplasia at spawning and survival thereafter. These three fishes show varying post-spawning outcomes from death of all the salmon to partial mortality in steelhead to usual survival of the rainbow trout. The adrenal cortical tissue, found in the cephalic end of the kidney, consists in the sexually immature fish of small isolated groups of characteristic cells which are usually associated with branches of the cardinal vein. With the onset of gonadal development the adrenal cells begin to increase in number and by the time sexual maturity is reached in the salmon and steelhead, marked hyperplasia is present. The cells of this hyperplastic tissue are larger than those in the immature fish and are uniform in size and appearance. In the spawning fish degeneration of the adrenal cells is evident—this is more marked in the salmon than in the steelhead trout—many of which show no degenerative change. In contrast to the salmon and steelhead, hyperplasia of the adrenal tissue in the non-migratory rainbow trout is very much less pronounced. The various factors which might operate to induce adrenal hyperplasia are discussed.