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This trial aimed to customize pikeperch (Sander lucioperca) larval nutrition using live feed enrichments based on Chlorella vulgaris and Trachydiscus minutus. Pikeperch larvae were fed with rotifers and Artemia enriched with C. vulgaris and T. minutus during the first 17 days after exogenous feeding (started 4 days post‐hatching [dph]) and only Artemia until 20 dph. Larvae were exposed to seven different enrichments: (a) Nannochloropsis occulata (Nanno 3600 reed Mariculture) (Control), (b) C. vulgaris cultured at 20°C in BG‐117 medium (BG20), (c) C. vulgaris cultured at 30°C in BG‐117 medium (BG30), (d) T. minutus cultured at 15°C (T15), (e) T. minutus cultured at 25°C (T25), (f) C. vulgaris cultured at 20°C in urea medium (U20), and (g) C. vulgaris cultured at 30°C in urea medium (U30). After 20 days, no significant differences were found between treatments on total length, standard length, myomere height, and eye diameter. On the contrary, significant differences were found in larval fatty acid composition after the trial period. Larvae from the BG30 treatment showed a significantly higher concentration of docosahexaenoic acid (5.61%), and larvae from the T25 treatment had a higher concentration of eicosapentaenoic acid 12.95%. Furthermore, larvae from the U20 treatment had a significantly higher arachidonic acid concentration of 0.116%. Overall, regarding essential fatty acid concentration, a significant difference was observed between the control treatment (Nannochloropsis) and the other treatments. No adverse effects were found on growth or survival when Nannochloropsis‐enriched live feed was replaced with the other enrichments. This trial's results will help optimize the pikeperch larvae's nutritional requirements and diversify the live feed enrichments used during the first feeding. [ABSTRACT FROM AUTHOR]

There is currently insufficient acknowledgment of the relationship between fish welfare and ultimate fillet quality. The purpose of this study was to assess the impacts of pre-slaughter handling and stocking density as fish welfare markers on fillet quality of largemouth bass ( Micropterus salmoides ). Fish from three stocking densities of 35, 50, and 65 kg·m -3 were reared in a recirculating aquaculture system (RAS) for 12 weeks and received commercial feed. Ultimately, the fish were either stunned with percussion on the head (control group) or subjected to air exposure for 3 min (anoxia group) before stunning and subsequent collection of blood and fillet samples. Western blot analysis revealed the degradation of actin in both groups. Additionally, higher oxidation progress and lower hardness and pH were observed in anoxia compared to the control group. We observed higher hardness at 35 kg·m -3 in anoxia compared to 50 and 65 km -3 . The initial hardness values at 35, 50, and 65 km -3 were 1073, 841, and 813 (g) respectively in the anoxia group. Furthermore, the anoxia and control groups had rigor mortis after 6 and 10 h, respectively. Cortisol and glucose levels, and oxidative enzymes activity were higher in anoxia than in the control group. In conclusion, oxidation induced by anoxia likely plays a crucial role as a promoter of the quality deterioration of largemouth bass fillets.

This study aimed to examine the ultrastructure of spermatogenic stages and mature spermatozoa in the European grayling, Thymallus thymallus . The testes were examined microscopically with a transmission electron microscope to find out details of the structure and morphology of the grayling germ cells, spermatozoa and some somatic cells. The grayling testis has a tubular shape, with cysts or clusters of germ cells within seminiferous lobules. The spermatogenic cells, including spermatogonia, spermatocytes, and spermatids, can be found along seminiferous tubules. There are electron-dense bodies in germ cells from the primary spermatogonia to secondary spermatocyte stages. These undergo mitosis to reach the secondary spermatogonia stage, when they form primary and secondary spermatocytes. Spermatids undergo three different stages of differentiation during spermiogenesis, characterized by the level of chromatin condensation, elimination of cytoplasm, and the occurrence of the flagellum. The midpiece of spermatozoa is short and contains spherical or ovoid mitochondria. The sperm flagellum has an axoneme with nine doublets of peripheral microtubules and two central microtubules. The result of this study is valuable to be used as a standard reference for germ cell development, which is of great importance to get a clear insight into the process of grayling breeding practice., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Dadras, Dadras, Imentai, Malinovskyi, Pěnka, Kolářová and Policar.)

Regarding the sperm of cold-water fish, the contributions of different bioenergetic pathways, including mitochondrial respiration, to energy production at the spawning temperature and its adaptation at the maximum critical temperature (CTmax) are unclear. The roles of glycolysis, fatty acid oxidation, oxidative phosphorylation (OXPHOS) at 4 °C, and OXPHOS at 15 °C for energy production in burbot ( Lota lota ) spermatozoa were studied by motility and the oxygen consumption rate (OCR) (with and without pathway inhibitors and the OXPHOS uncoupler). At both temperatures, the effects of the inhibitors and the uncoupler on the motility duration, curvilinear velocity, and track linearity were insignificant; in addition, the OCRs in activation and non-activation media differed insignificantly and were not enhanced after uncoupler treatment. After inhibitor treatment in both media, OXPHOS was insignificantly different at the 2, 30, and 60 s time points at 4 °C but was reduced significantly at the 30 and 60 s time points after treatment with sodium azide at 15 °C. In conclusion, for burbot sperm at both the spawning temperature and the CTmax, the energy synthesized via OXPHOS during motility was insufficient. Therefore, the majority of the energy required to sustain motility was derived from pre-accumulated energy produced and stored during the quiescent state of the spermatozoa.

Although ruffe (Gymnocephalus cernua) are widely distributed in Eurasia, in some regions (i.e., North America) ruffe are considered an invasive species. There have been no reports on artificial reproduction of this species. A study, therefore, was conducted to evaluate reproduction of ruffe with results of specimens captured from their natural habitat and cultured (F 1 generation) specimens being compared. Spawning specimens from both stocks were treated with hormonal preparations: carp pituitary homogenate (CPH), Ovopel, Ovaprim and human chorionic gonadotropin (hCG) and results were analyzed by comparing response to the specimens of control groups. Spermiation outcomes and sperm motility of the captured and cultured ruffe were similar and with all hormonal treatments, there was a slightly greater sperm motility (55.6 %-57.1 %) in comparison to specimens of control groups (46.7 %-47.1 %). For captured specimens, there was no asynchronous development of oocytes, whereas in cultured specimens 32 % of females had asynchronous development of oocytes. The ovulation rate in specimens of all treated groups was 100 %, whereas specimens in the control groups did not reproductively mature and have ovulations. The latency time from time of hormonal treatments to initiation of reproductive functions depended on the spawning agent used and oocyte maturation stage and there was the shortest latency after using CPH and the longest with hCG treatment. The embryo survival and hatching rates varied with use of different hormonal preparations to induce reproduction: greatest hatching rates with hCG treatment (86.4 %-88.9 %), followed by Ovaprim (78.2 %-80.2 %) and least hatching rate with Ovopel and CPH treatments (66.0 %-67.1 % and 64.0 %-66.0 %, respectively)., (Copyright © 2020 Elsevier B.V. All rights reserved.)

This study focused on supplementing pikeperch ( Sander lucioperca ) larvae with rotifers fed with Chlorella vulgaris during the first 15 days post hatching (dph). Larvae were fed a combination of rotifers and artemia under three different enrichments: A) Nannochloropsis occulata , B) Chlorella vulgaris , and C) a commercial enrichment-Selco, Spresso from INVE. After 17 days from the trial initiation differences were found between treatments on survival rate, myomere height (MH), fatty acid composition, and stress tolerance. In terms of survival, larvae from treatment b (74.5%) and c (66%) excelled over the control (a) treatment (59%). Furthermore, larvae from both the Chlorella (b) and the Selco (c) treatments showed more resilience to stress conditions (10% and 37% reduction in mortality) when exposed to high salinity conditions (18ppt) for 3 h (stress response). Overall, larvae from treatments b and c performed better than those receiving a non-enriched diet (a), likely due to the higher levels of Essential Fatty Acids (EFA) and the ability of pikeperch to desaturate and elongate fatty acids (FA) with 18 carbons to LC PUFAs (Polyunsaturated Fatty Acids). The present study provides valuable input for designing improved feeding protocols, which will increase the efficiency of pikeperch larval culture.

This trial tested the use of lactic acid bacteria (LAB) on pikeperch ( Sander lucioperca ) larvae during their first feeding. The trial included the use of two probiotic treatments and one control (no probiotics). Pikeperch larvae were exposed to LAB as follows: (1) the live feed (Treatment 1, live feed) or (2) via the live feed and the larval rearing water (Treatment 2, probiotic). Significant differences were found between the treatments in terms of total length (TL), myomere height (MH), overall survival, and the tolerance to a high salinity challenge. Larvae exposed to LAB via both the live feed and the rearing water had a significantly higher overall survival rate (85%) than the other two treatments at 21 dph. When both treatments were subjected to high salinity rates (18 parts per thousand (ppt)), both treatments exposed to LAB demonstrated higher survival rates than the control treatment (28% and 40% survival rate at 180 min for the live feed and probiotic treatments, respectively, as compared with a 100% mortality rate at 150 min for the control). At the same time, larvae exposed to the probiotic treatment had a significantly higher TL as compared to the control after 12 and 21 days post hatch (dph) (probiotic 7.13 ± 0.21 and 11.71 ± 1.1 mm, control 5.86 and 10.79 mm at 12 and 21 dph, respectively). The results suggest that the use of LAB in both the live feed and the rearing water has a positive effect on pikeperch larval quality by strengthening their resilience to stress conditions, as well as improving the growth and survival rates., Competing Interests: The authors declare no conflict of interest.

The aim of this study was to compare the spermatozoa quality parameters in spermatozoa of RAS (Recirculating Aquaculture System; RAS group) cultured (commercial pellets) and natural condition cultured (WILD group) burbot Lota lota (live prey, Pseudorasbora parva). Seven of nine fish of the RAS group produced sperm, with sperm from only four of the fish having a motility of >5%. Sperm were collected from all nine fish of the WILD group, and sperm of six of the fish from the WILD group had motility of about 100% and three had sperm with 50% to 60% motility. Spermatozoa from the RAS group had a delay in activation compared to the WILD group. Fish from the RAS group also had a lesser volume of sperm (1.8 ± 1.2 mL) collected compared to the WILD group (3.6 ± 1.2 mL). Compared to the RAS group, sperm of the WILD group had a greater proportion of saturated fatty acids (SFA), as well as the phospholipid, phosphatidylethanolamine. The findings indicate that fish grown in natural conditions may be more suitable as broodstock. Ongoing research to develop methods of enhancing reproductive performance of burbot broodstock cultured in RAS is needed to investigate whether the quality of sperm can be improved by adjusting environmental conditions, diet, or combination of these factors., (Copyright © 2018 Elsevier B.V. All rights reserved.)