This paper compares some morphological and endocrinolog~cal 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 I 1 -ketotestosterone in triploid and diploid males were not significantly different. However, levels of testosterone and 17P-oestradiol in diploid females were considerably higher than those of triploid females.
Plasma growth hormone concentrations were determined in diploid and triploid rainbow trout of both sexes during sexual maturation. Diploid females grow large ovaries, whereas triploid female trout show no ovarian development. The plasma growth hormone concentration in triploid female trout remained low and unchanged throughout the study, whereas it rose slightly, but significantly, in the diploid females that matured, but not in those that remained immature. On the other hand, triploid males do develop testes like their diploid counterparts. In both groups spermiation was accompanied by a steady rise in the plasma growth hormone concentration. The results suggest that the elevated growth hormone concentration in mature male trout was a consequence not of reproduction per se, but of the loss of condition that accompanied spawning. This hypothesis was supported by the results from the females. Apart from a temporary loss in the mature diploids caused by stripping of the eggs, female trout did not lose condition, neither did they show any change in the plasma growth hormone concentration during the period when they ovulated. These results suggest that it was the nutritional insuffrciency accompanying reproduction in male fish that caused the elevation in growth hormone concentration. In fact, a strong negative correlation between the plasma growth hormone concentration and the condition factor of the fish was observed. Q
Triploid male plaice, Pleuronectes platessa, and plaice x flounder, PlatichthysJlesus, hybrids produced from cold-shocked eggs were reared to maturity at three years ofage. The testes of triploid hybrids were similar in macroscopic appearance and size to those from control fish but in histological section spermatocyte and spermatid cell formation was grossly abnormal. In two fish the majority of cells appeared to be aborted spermatids and spermatocytes although there were some spermatozoa with enlarged heads and thick bent flagellae.The testes of mature triploid plaice were similar to controls both in shape and size and in histological section. Spermatocyte and spermatid cell formation was normal, apart from an increase in cell and nuclear size, and fully motile spermatozoa were produced from several fish. Plaice eggs fertilized with semen from triploids showed a slight reduction in fertility compared with controls but developed normally to gastrulation with little mortality. Beyond gastrulation there was increasing mortality associated with abnormalities in the appearance of embryos. Few hatched and none of these survived longer than 48 h. The value of triploidy in fish farming is briefly discussed.
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