OOCYTE DEVELOPMENT OF BILATERAL SALMON (SALMO SALAR L., 1758) AND SEA TROUT (SALMO TRUTTA M. TRUTTA L., 1758) HYBRIDS AND PURE SPECIES IN THE FRESHWATER PERIOD OF THEIR LIFE

摘要

The experiment was performed on the gonads of the following: 205 females of the hybrids ♀ Salmo trutta m. trutta × ♂ Salmo salar , 64 females of the hybrids ♀ Salmo salar × ♂ Salmo trutta m. trutta , 120 female trout and 120 female salmon, aged 0+, 1+. The fish were obtained from 8 experiments, in which a reciprocal cross was made of salmon and trout caught in their natural environment. The hybrids grew in small watercourses which do not join open waters. The watercourses are in the Bukowa Forest. The hybrids and the salmon and trout were caught in cycles. After the fish were caught, they were weighed, measured and their gonads were cut out and fixed. Histological preparations were made and the gonad stages and the degree of oocyte development and oocyte size were analysed. Results showed that the gonads of females of reciprocal hybrids aged 0+ or 1+ were in developmental stage I or II. In the second stage of gonadal development these oocytes reached 1, 2, 3~(o) of protoplasmatic growth, while in the gonads of salmon and sea trout, oocytes reached 4~(o) protoplasmatic growth. In the hybrids, ♀ trout × ♂ salmon remained at stage I till the age of 14 months, while in the reverse hybrid till the age of 9 months. This is much longer than in species in which parents at the age of 4 months, were in stage II. In addition, a distinctive feature of hybrids from parental species was that in the gonads of all female hybrids, of the two oocytes there were only 1–3~(o) protoplasmatic growth (second stage of development of the gonads), and in the parent species growth was more advanced. In hybrids protoplasmatic growth of oocytes in the sections of the gonad were few, with salmon and sea trout filling the entire cross-section of gonad.