Characteristics of the Sertoli Cells of Salmonidae from Ohrid Lake during Spermatogenesis-Ultrastructural Analysis

Ultrastructual characteristics of Sertoli cells of Salmonidae from Ohrid Lake during the spermatogenetic cycle have been analysed. Sertoli cells being an integral part of the seminiferous lobules underwent considerable changes, which influenced their cytomorphological features. The degenerative changes of Sertoli cells were manifested by an extreme vacuolisation, mitochondria in degeneration with widened crysts and thickened matrix, desorganised ER, autophagosomes, ＂myeline-like＂ structures and lysed cytoplasmic regions. The above mentioned changes were followed by karyopycnisis, comlete degeneration and delamination of cells from the wall of the seminiferous lobules, lysis and detritus formations （Sertoli necrotic material） in the lumen of the lobules. The aim of this paper is special research of the ultrastructural characteristics, i.e. the changes on a level with testes which happen in the postspawning period in the two species of Teleostei of Ohrid Lake, Ohrid trout （Salmo letnica Kar.） and Ohrid belvica （Acantholingua ochridana Steind.）. The postspawning period is emphasized in Teleostei in this relatively short period, when one reproductive cycle finishes and the following has to start, on a level of testicular parenhyma very important histological changes are going on which give special histological identification, i. e. in the postspawning period there is a complete reorganization of the testes.

Comparative Evaluation of Toleration to Heating and Hypoxia of Three Kinds of Salmonids

This study was conducted to evaluate the critical thermal maximum(CTMax), the routine metabolism rate(MO_2) and the limiting oxygen saturation(LOS) of three salmonids with four different body weights ranging from 16 g to 131 g. The CTMax was estimated at three different heating rates including 0.5℃ min^(-1), 1℃ h^(-1) and 2℃ d^(-1). Results showed that the CTMax of maple trout(Oncorhynchus mykiss) was the highest, which was followed by steelhead trout(O. mykiss) and Atlantic salmon(Salmon salar). The CTMax of the salmonid fish decreased with the increment of body weight, and was significantly influenced by the heating rate. The MO_2 of the salmonid fish increased with the increment of temperature, and decreased with the increment of body weight. Suffocation points of the fish decreased with increasing body weight and temperature. Steelhead trout was more tolerant to hypoxia than maple trout and Atlantic salmon, while the MO_2 of Atlantic salmon was the highest among these three salmonids. The LOS of the fish generally had a positive trend with temperature and body weight, and the LOS of steelhead trout was significantly lower than that of maple trout and Atlantic salmon. In conclusion, maple trout was the most tolerant kind to high temperature, while steelhead trout was the most tolerant to hypoxia among three kinds of salmonids. Moreover, the abilities to tolerate higher temperature of three salmonids were affected by their body weight and the heating rate, while the abilities to tolerate hypoxia were influenced by their body weight and the water temperature.

Behavioral type,in interaction with body size,affects the recapture rate of brown trout Salmo trutta juveniles in their nursery stream

Movement activity levels of wild animals often differ consistently among individuals,reflecting different behavioral types.Previous studies have shown that laboratory-scored activity can predict several ecologically relevant characteristics.In an experiment on wild brown trout Salmo trutta,spanning from June to October,we investigated how spring swimming activity,measured in a standardized laboratory test,related to relative recapture probability in autumn.Based on laboratory activity scores,individuals clustered into 2 groups,which showed contrasting patterns in the size-dependency of their recapture probability.Size had a slightly positive effect on recapture probability for passive fish but a clear negative effect on active fish.Our results show that the population structure in a cohort,in terms of relative proportions of behavioral types in different size classes,can vary over time.The results of this study could depend on either selective mortality or migration.However,selective disappearance of individuals with specific phenotypes,regardless of the mechanism,will have implications for trout population management,such as stocking efficiency of hatchery fish with high growth rates or maintenance of fishways past migration barriers.