Sexual maturation in triploid rainbow trout, <i>Salmo gairdneri</i> Richardson

Abstract

This paper compares some morphological and endocrinological characteristics of diploid and triploid rainbow trout. Significant differences were found between diploid and triploid females in GSI, condition factor, gut weight, liver weight and percentage dress‐out, and between diploid and triploid males in GSI, condition factor and gut weight. Diploid females had large, well‐developed ovaries containing yolk‐filled secondary oocytes whereas the triploids had only string‐like ovaries containing nests of oogonia. No primary oocytes were present. All the diploid males produced copious quantities of milt but it was possible to express a thin, watery milt containing motile spermatozoa from only two of the 12 triploid males. Testes weights in triploids were similar to those of diploids but, while the diploid testes were packed with spermatozoa, those of the triploids consisted mainly of spermatocytes and spermatids with few spermatozoa present. Measurements of the heads of spermatozoa revealed that those from triploids were larger and had a wider size range than those from diploids. Levels of testosterone and 11‐ketotestosterone in triploid and diploid males were not significantly different. However, levels of testosterone and 17β‐oestradiol in diploid females were considerably higher than those of triploid females.