Histological changes in the testis in the sexual cycle of male salmon parr ( Salmo salar L. juv.)

A histological examination of the parr testis was begun in conjunction with an investigation of the occurrence of the male sexual stage in salmon parr (Orton, Jones and King 1938; Jones and Orton 1940). It became apparent that histological preparations were necessary in order to ascertain definitely whether testes which had been classified as “spent” or “empty” belonged to fish that had spawned, and whether it was possible to distinguish by macroscopic examination between and undeveloped and a spent testis. Subsequently it was considered desirable to follow out histologically the complete cycle from the earliest stage sampled to the spent condition and after. The fish examined were mostly killed on the riverside and the material fixed in Bouin’s fluid. Some formalin material was also used. After cutting at about 5-7μ the sections were stained with Ehrlich’s haematoxylin or Heidenhain’s iron haematoxylin, both being counterstained with eosin. Staining with Mallory’s triple stain proved unsuccessful.