GONADAL MORPHOLOGY OF NORMAL AND SEX-REVERSED TRIPLOID AND GYNOGENETIC DIPLOID COHO SALMON (ONCORHYNCHUS-KISUTCH)

In this study, the gonadal morphology of untreated and sex-reversed ju venile triploid and gynogenetic diploid coho salmon was compared with that of diploids. Testes of triploids were of the same size as those o f diploids. Spermatogonia, however, were significantly bigger than tho se of diploids in both diameter (P<0.001) and volume (p<0.01), suggest ing that this characteristic can be a useful indicator of ploidy in th e early stages of gonadal development. In females, induction of triplo idy did not affect the lamellar structure of the ovaries but reduced t heir size considerably. Further, these ovaries had no oocytes. Treatme nt of triploids with oestrogen resulted in the feminization of genotyp ic males, which had ovaries similar to those found in triploid females . However, gonads of triploid males partially sex-reversed into female s were identified by their enlargement, the presence of remnants of th e male vascular system, and by the appearance of ovarian lacunae and g erminal and somatic cells typical of triploid females. Induction of gy nogenesis resulted in 100% females, of which 34% had ovaries of reduce d size with areas devoid of oocytes. However, and contrary to what has been found in cyprinids, no male germ cells were observed in these ov aries. This discrepancy may reflect differences in the mechanisms of s ex determination between salmonids and cyprinids. Treatment of gynogen etics with androgen increased the number of fish with abnormal ovaries but also resulted in the production of phenotypic-male gynogenetic di ploids, of which 11% had testes indistinguishable from those of untrea ted control diploids.