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Efficient, cost-effective DNA extraction methods are crucial for molecular research on sturgeon embryos given that substantial sample sizes must frequently be analyzed in short periods of time. The high lipid and carbohydrate contents of sturgeon embryo yolk sacs mean that obtaining genetic material of sufficient quality is challenging. The predominant methods used include tissue/cell lysis, organic extraction, purification on spin columns, and ethanol precipitation. However, these methods are expensive and time-consuming, which significantly limits the throughput of PCR-based molecular analyses. In the present study, we evaluated the usefulness of an in-house Chelex-100 DNA extraction method on sterlet (Acipenser ruthenus) embryos at the neurula developmental stage (48 hours post fertilization) and compared it with two other commercial silica membrane-based kits for isolating genetic material–NucleoSpin Tissue® (Macherey Nagel, Duren, Germany) and Sherlock AX (A&A Biotechnology, Gdynia, Poland). The yield and quality of nucleic acid, its suitability for PCR amplification, and the total cost and complexity of the extraction methods were evaluated and compared. Our results indicated that the in-house Chelex-100 is inexpensive and can be used as an effective high-throughput method of DNA isolation for sterlet embryos.

European catfish, Silurus glanis L., is the second largest freshwater fish in Europe. The species is very popular among the farmers, as it is one of the most promising European aquaculture species. Despite the growing importance of European catfish in freshwater aquaculture, the genetic data available on this species are still limited. The main purpose of the present study was to develop a reliable, feasible genetic protocol for future studies on European catfish populations and broodstocks in Poland. The genetic characteristics of the tested fish group were based on genetic parameters such as the polymorphism information content (PIC), the effective population size (Ne), the inbreeding coefficient (Fis), and the Garza-Williamson index (M), among others. Additionally, the potential effects of a genetic bottleneck on the genetic variation of the broodstock were examined. The genetic analysis protocol described in this study can be used to establish genetic-based records for European catfish broodstocks, including for sperm cryobanking. This approach will be useful for elaborating the selection procedures that allow for optimal assemblages of spawning pairs in artificial reproduction. The application of the genetic analysis protocol in practice will permit maintaining high quality in European catfish broodstocks.

Expression of the telomerase reverse-transcriptase (TERT) gene and activity of telomerase have been reported in the somatic tissues and gonads in fish irrespective of their age and size. Nevertheless, little is known about TERT expression in the fish eggs. In the current study, the presence of the TERT transcripts was confirmed in the rainbow trout ovulated eggs before and after activation with nonirradiated and UV-irradiated (gynogenesis) sperm. Eggs originating from eight females had high and comparable quality expressed by similar hatching rates. However, survival of the gynogenetic larvae that hatched from eggs activated with UV-irradiated sperm and further exposed to the high hydrostatic pressure (HHP) shock for duplication of the maternal chromosomes varied between females from 2.1 ± 0.4 to 40.5 ± 2.2%. Increased level of TERT transcripts was observed in eggs originating from two females, and gametes from only one of them showed improved competence for gynogenesis (27.3 ± 1.9%). In turn, eggs from the female that exhibited the highest survival after gynogenetic activation were characterized by the lowest expression of the TERT gene. Telomerase in rainbow trout eggs may compensate erosion of the telomeres during early embryonic development; however, its upregulation does not assure better development after gynogenetic activation., Competing Interests: Declarations Ethics approval The study was carried out in strict accordance with the recommendations in the Polish Act of 15 January 2015 on the Protection of Animals Used for Scientific or Educational Purposes, Journal of Laws 2015, item 266. The protocol was approved by the Local Ethical Committee for the Experiments on Animals in Bydgoszcz (resolution no. 27/2022). Conflict of interest The authors declare no competing interests., (© 2024. The Author(s).)

The phenotype, genetic sex ratio and gonadal development characteristics were evaluated in randomly selected juvenile (15 months old), sub-adult (22 months old) and adult (30 months old) triploid hybrids of rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis). The examined fish originated from the family produced by application High Hydrostatic Pressure (HHP) shock (9500 psi for 5 minutes, applied 35 minutes post-fertilization at 10°C) to eggs stripped from five rainbow trout females and fertilized with sperm of two brook trout males. After hatching, all fish were reared under the same conditions for three years. The ploidy level and hybrid status of the fish were confirmed through cytogenetic analysis and DNA genotyping. Three distinct phenotypes; trout-like (Tr-l) phenotype, salmon-like (Sa-l) phenotype and intermediate (Tr/Sa-l) phenotype, with the following frequencies: f= 50.8 %, f= 31.7 % and f= 17.5 %, respectively, were observed among the sampled specimens. Genetic males exclusively detected among individuals with Tr-l phenotype developed macroscopically visible and histologically functional testes in their second year of life, representing the lowest value for the aquaculture production. A comparable proportion of males and females was recorded among individuals with Sa-l and Tr/Sa-l phenotypes. Males with these phenotypes developed macroscopically distinguishable and histologically functional testes in their third year of life. In the genetic males, underdeveloped intersex or completely reduced gonads were recorded. This study revealed that individuals with Sa-l phenotype represent the greatest value for commercial production because of their unique appearance and complete sterility (females) or delayed maturation observed only after reaching the market size (males)., Competing Interests: Declaration of Competing Interest None of the enclosed material has been published and is under consideration elsewhere, including on the Internet. All the authors have approved the manuscript for submission. None of the authors have any conflict of interest to declare., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

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.

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, Władysławowo, the Vistula Lagoon in 2018, and the Słupsk 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 Słupsk Bank. The estimated effective population size ( Ne ) among the sampled fish groups varied from 712 (Słupsk Bank) to 10,115 (Władysławowo 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.

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.

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., (Copyright © 2022 Elsevier B.V. All rights reserved.)