An opinion paper: emphasis on white muscle development and growth to improve farmed fish flesh quality

Pikeperch muscle tissues: a comparative study of structure, enzymes, genes, and proteins in wild and farmed fish

Pikeperch (Sander lucioperca) is a freshwater species and an internationally highly demanded fish in aquaculture. Despite intensive research efforts on this species, fundamental knowledge of skeletal muscle biology and structural characteristics is missing. Therefore, we conducted a comprehensive analysis of skeletal muscle parameters in adult pikeperch from two different origins, wild-caught specimens from a lake and those reared in a recirculating aquaculture system. The analyses comprised the biochemical characteristics (nucleic acid, protein content), enzyme activities (creatine kinase, lactate dehydrogenase, NADP-dependent isocitrate dehydrogenase), muscle-specific gene and protein expression (related to myofibre formation, regeneration and permanent growth, muscle structure), and muscle fibre structure. The findings reveal distinct differences between the skeletal muscle of wild and farmed pikeperch. Specifically, nucleic acid content, enzyme activity, and protein expression varied significantly. The higher enzyme activity observed in wild pikeperch suggests greater metabolically activity in their muscles. Conversely, farmed pikeperch indicated a potential for pronounced muscle growth. As the data on pikeperch skeletal muscle characteristics is sparse, the purpose of our study is to gain fundamental insights into the characteristics of adult pikeperch muscle. The presented data serve as a foundation for further research on percids' muscle biology and have the potential to contribute to advancements and adaptations in aquaculture practices.

Chemical and Physical Properties of African Catfish (Clarias gariepinus) Fillet Following Prolonged Feeding with Insect Meal-Based Diets

A 25-week experiment was undertaken to explore the effect of partial replacement of dietary fishmeal (FM) with black soldier fly meal (Hermetia illucens) (BS), mealworm meal (Tenebrio molitor) (MW), and a 1 : 1 mixture of both insect meals (BSMW) on fillet quality in African catfish (Clarias gariepinus). A total of 96 fish with an average initial body weight of 248 ± 28 g were stocked into a recirculating aquaculture system and fed in four different dietary groups (control, BS, MW, and BSMW). No mortality was recorded in any of the groups. At the end of the feeding period, 24 fish (n = 6 for each treatment, weight between 690 and 822 g) were used for analysis. There was no alteration in filleting yield or other slaughter indices within experimental groups, except the hepatosomatic index. Among quality attributes, pH 24 hr postmortem exhibited a significant difference (p < 0.05). In respect of the fatty acid profile, the n-6/n-3 ratio ranged between 1.17 and 1.40 but was not significantly modified by the partial replacement of FM. Similarly, the proximate composition of the fillets was not significantly different between the control and experimental diet groups. The ratio of polyunsaturated fatty acid to saturated fatty acids ranged between 0.67 and 0.79 in the fillets, without significant differences between groups. The atherogenic index was increased in the BS group, as compared to the others; however, the thrombogenicity index of fillets was not significantly affected. Similarly, the conventional quality traits of the fillet, such as cooking, drip, and thawing losses, did not differ within treatments. This study demonstrates that the dietary inclusion of black soldier fly and/or mealworm meals used for African catfish at the tested inclusion level has negligible impact on fillet properties.