Pikeperch is a new focus species in freshwater aquaculture. It has large economical potential as it already has a broad consumer base as well as the biological capability to produce large numbers of offspring (Lappalainen et al., 2003;Steenfeldt et al., 2015). Still, it is rare in aquaculture, as high mortality rates occur during its rearing and husbandry (Policar et al., 2019). This is especially severe during the early development between embryonic and larval ontogeny. During this period, the loss of around half or more of the reared specimens can occur, which highly affects the economic success of pikeperch aquaculture (Ostaszewska et al., 2005;Szkudlarek & Zakęś, 2007).Several developmental changes occur during this time including late embryonic organ formation, hatching, the transition from endogenous to exogenous feeding and several organ changes connected to

Rising temperatures can affect fish survival, especially from shallower waters, as temperatures increase faster and more intensively in these areas; thus, species-specific temperature tolerance can be exceeded. Additionally, the amounts of anthropogenic pollutants are higher in coastal waters. Although increasing metabolic activity at higher temperatures could lead to stronger effects of toxins, there are hardly any studies on this topic. Subsequently, the aim was to investigate the response of fish cells upon exposure to industrial solvents (ethanol, isopropanol, dimethyl sulfoxide (DMSO)) in relation to a temperature increase (20 °C and 25 °C). Concerning the 3Rs (the replacement, reduction and refinement of animal experiments), in vitro tests were used for two threatened, vulnerable fish species: maraena whitefish (Coregonus maraena) and Atlantic sturgeon (Acipenser oxyrinchus). Both cell lines exhibited higher proliferation at 25 °C. However, ecotoxicological results indicated significant differences regarding the cell line, toxin, temperature and exposure time. The evolutionarily older fish lineage, Atlantic sturgeon, demonstrated lower mortality rates in the presence of isopropanol and recovered better during long-term ethanol exposure than the maraena whitefish. Atlantic sturgeon cells have higher adaptation potential for these alcohols. In summary, fish species respond very specifically to toxins and changes in temperature, and new ecotoxicological questions arise with increasing water temperatures.

The growth of fishes and their metabolism is highly variable in fish species and is an indicator for fish fitness. Therefore, somatic growth, as a main biological process, is ecologically and economically significant. The growth differences of two closely related salmonids, rainbow trout (Oncorhynchus mykiss) and maraena whitefsh (Coregonus maraena), have not been adequately studied as a comparative study and are therefore insufficiently understood. For this reason, our aim was to examine muscle growth in more detail and provide a first complex insight into the growth and muscle metabolism of these two fish species at slaughter size. In addition to skeletal muscle composition (including nuclear counting and staining of stem and progenitor cells), biochemical characteristics, and enzyme activity (creatine kinase, lactate dehydrogenase, isocitrate dehydrogenase) of rainbow trout and maraena whitefish were determined. Our results indicate that red muscle contains cells with a smaller diameter compared to white muscle and those fibres had more stem and progenitor cells as a proportion of total nuclei. Interestingly, numerous interspecies differences were identified; in rainbow trout muscle RNA content, intermediate fibres and fibre diameter and in whitefish red muscle cross-sectional area, creatine kinase activity were higher compared to the other species at slaughter weight. The proportional reduction in red muscle area, accompanied by an increase in DNA content and a lower activity of creatine kinase, exhibited a higher degree of hypertrophic growth in rainbow trout compared to maraena whitefish, which makes this species particularly successful as an aquaculture species.

Pikeperch (Sander lucioperca) is a freshwater fish that has become increasingly popular as a food fish. Within this study, the influence of the spawning process on meat quality was investigated. For this purpose, adult pikeperch was examined directly before and after spawning, and compared regarding physical meat parameters and lipid composition. The results indicate that after spawning, the values of the pH, the electrical conductivity and the yellowness value of fillet were significantly higher than those of the animals sampled before spawning. Analysis of the sum of the total lipid content indicates no differences before and after closed season, but differences in the fatty acid profile were present. Despite significant lower MUFA concentrations, the EPA and DHA showed unaffected high contents. Therefore, the fish muscle indicated an equivalent meat quality. Nevertheless, the significant changes of some physical meat quality parameters after spawning season could have a particular impact on the shelf life and storage of the pikeperch fillet, highlighting the need for further research.

In this study, a cell line of the fish species Coregonus maraena was produced for the first time. C. maraena is an endangered species, and studies indicate that this fish species will be affected by further population declines due to climate change. This cell line, designated CMAfin1, has been maintained in Leibovitz L‐15 supplemented with 10% fetal bovine serum over 3 years. Both subculturing and storage (short‐term storage at −80°C and long‐term storage in liquid nitrogen) was successful. Cell morphology and growth rate were consistent from passage 10 onwards. Immunocytochemical examination of cellular proteins and matrix components confirmed the mechanical stability of the cells. Actin, fibronectin, vinculin, vimentin, and tubulin are present in the cells and form a network. In addition, the transport of molecules is ensured by the necessary proteins. Gene expression analysis showed a shift in the expressions of stem cell markers between younger and higher passages. While SOX2 and IGF1 were more highly expressed in the seventh passage, SOX9 and IGF2 expressions were significantly increased in higher passages. Therefore, the stable cell culture CMAfin1 can be used for applied analysis to further understand the cell physiology of C. maranea.