Telomerase Activity in Somatic Tissues and Ovaries of Diploid and Triploid Rainbow Trout (Oncorhynchus mykiss) Females.

Telomerase activity has been found in the somatic tissues of rainbow trout. The enzyme is essential for maintaining telomere length but also assures homeostasis of the fish organs, playing an important role during tissue regeneration. The unique morphological and physiological characteristics of triploid rainbow trout, when compared to diploid specimens, make them a promising model for studies concerning telomerase activity. Thus, in this study, we examined the expression of the Tert gene in various organs of subadult and adult diploid and triploid rainbow trout females. Upregulated Tert mRNA transcription was observed in all the examined somatic tissues sampled from the triploid fish when compared to diploid individuals. Contrastingly, Tert expression in the ovaries was significantly decreased in the triploid specimens. Within the diploids, the highest expression of Tert was observed in the liver and in the ovaries of the subadult individuals. In the triploids, Tert expression was increased in the somatic tissues, while the ovaries exhibited lower activity of telomerase compared to other organs and decreased compared to the ovaries in the diploids. The ovaries of triploid individuals were underdeveloped, consisting of only a few oocytes. The lack of germ cells, which are usually characterized by high Tert expression, might be responsible for the decrease in telomerase activity in the triploid ovaries. The increase in Tert expression in triploid somatic tissues suggests that they require higher telomerase activity to cope with environmental stress and maintain internal homeostasis.

Population Genetic Study on the European Flounder (Platichthys flesus) from the Southern Baltic Sea Using SNPs and Microsatellite Markers.

The European flounder (Platichthys flesus), which is closely related to the recently discovered Baltic flounder (Platichthys solemdali), is currently the third most commercially fished species in the Baltic Sea. According to the available data from the Polish Fisheries Monitoring Center and fishermen's observations, the body condition indices of the species in the Baltic Sea have declined in recent years. The aim of the present study was to obtain information on the current patterns of genetic variability and the population structure of the European flounder and to verify whether the Baltic flounder is present in the southern Baltic Sea. Moreover, we aimed to verify whether the observed decline in the body condition indices of the species in the Baltic Sea might be associated with adaptive alterations in its gene pool due to increased fishing pressure. For this purpose, 190 fish were collected from four locations along the central coastline of Poland, i.e., Mechelinki, Wladyslawowo, the Vistula Lagoon in 2018, and the Slupsk Bank in 2020. The fish were morphologically analyzed and then genetically screened by the application of nineteen microsatellite DNA and two diagnostic SNP markers. The examined European flounder specimens displayed a high level of genetic diversity (PIC = 0.832-0.903, I = 2.579-2.768). A lack of significant genetic differentiation (Fst = 0.004, p > 0.05) was observed in all the examined fish, indicating that the European flounder in the sampled area constitutes a single genetic cluster. A significant deficiency in heterozygotes (Fis = 0.093, p < 0.05) and overall deviations from Hardy-Weinberg expectations (H-WE) were only detected in fish sampled from the Slupsk Bank. The estimated effective population size (Ne) among the sampled fish groups varied from 712 (Slupsk Bank) to 10,115 (Wladyslawowo and Mechelinki). However, the recorded values of the Garza-Williamson indicator (M = 0.574-0.600) and the lack of significant (p > 0.05) differences in Heq > He under the SMM model did not support the species' population size changes in the past. The applied SNP markers did not detect the presence of the Baltic flounder among the fish sampled from the studied area. The analysis of an association between biological traits and patterns of genetic diversity did not detect any signs of directional selection or density-dependent adaptive changes in the gene pool of the examined fish that might be caused by increased fishing pressure.

Telomerase Activity in Androgenetic Rainbow Trout with Growth Deficiency and in Normally Developed Individuals.

Role of telomerase in specimens with retarded growth (dwarfs) has not been thoroughly examined to date. Considering that some of the fish species show correlation between somatic growth and activity of telomerase, it has been tempting to assume that pattern of telomerase activity in specimens with retarded growth and these with normal growth rate may vary. In the present research, telomerase activity has been examined in liver, skin, and muscles in the androgenetic rainbow trout (Oncorhynchus mykiss) with growth deficiency and their normally developed siblings. Among the examined organs, the liver showed the highest telomerase activity in all studied fish, what may be linked to the enormous regeneration capacity of the liver tissue. Although dwarf specimens examined here displayed significantly lower body size and weight they did not exhibit any significant differences in the telomerase activity measured in liver and muscle when compared to the rainbow trout without growth deficiency. In turn, telomerase activity in skin was significantly upregulated in the normally developed androgenotes. The present study indicates that dwarfism in the androgenetic rainbow trout is neither associated with ceased telomerase activity nor its decrease throughout the ontogenetic development.

An efficient protocol for chromosome isolation from sterlet (A. ruthenus) embryos and larvae.

In the present manuscript an efficient and feasible protocol for chromosome preparation from sterlet (A. ruthenus) embryos and larvae was developed that can be used as routine molecular diagnostic tool of the species genome manipulation procedures verification. For this end, a multi-dimensional experimental system was conceived that enabled for the establishment of chromosome preparation protocol, which characterized the mean efficiency of chromosome extraction ranged from 70% to 100% and the average number of recorded metaphases per slide ranged between 9 and 15. The developed under the current study protocol can be used as a fast and reliable tool, alternative for flow cytometry techniques that enable for the molecular verification of genome manipulations effectiveness. As genome engineering is presently the fundamental biotechnology tool that enables for effective and sustainable aquaculture of fish, including sturgeons that are known as one of the most valuable economically and ecologically fish group, the development of easy and fast methods for the verification of genome manipulation effects is especially important. Thus, the established chromosome preparation protocol contributes to genome and reproduction studies of sturgeons, including taxonomy, inter-species hybridization, genome aberrations, sex determination system and selection. Moreover, the application of cytogenetic techniques also contributes to the development of new or improvement existing techniques of genome engineering utilized in sturgeon aquaculture.