Abstract: | The histological and ultra-structure of the pituitary in diploid red crucian carp (Carassius auratus red var.), triploid crucian carp and allotetraploid hybrids within and after the breeding season were comparatively studied.
The result showed that there were six endocrine cell types in the pituitary of these three kinds of fishes, and there was
an obvious difference in cell size among different ploidy level fishes. As for the same type of pituitary cells, the cell
size was increased gradually with the increasing ploidy level. In the breeding season, the allotetraploid hybrids had higher
proportion of gonadotropin cells (GTH) than triploids, and the trploids had higher proportion of GTH than diploids. The results
were related to the earlier sexual maturity of allotetraploid hybrids and sterility of triploid crucian carp. On the other
hand, among the three kinds of fishes, the proportion of somatotropin (STH) cells in triploids crucian carp was the highest,
whereas that in allotetraploid hybrids was the lowest. The results might be connected with the faster growth rate of triploids
and slower growth rate of allotetraploid hybrids. In addition, in GTH cells of meso-adenohypophysis after the breeding season,
there were many endocrine particles in triploids, while those endocrine particles were released from the cells in allotetraploids
and diploids. This result showed that the sterility of triploid crucian carp might be related to the hormone which was not
released from the GTH cells. In a word, the present study indicated that the differences in the structure of pituitary among
different ploidy level fishes contributed to their difference in the growth rate and gonadal development. |