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Homogeneous background (age, sex, genetic lineage, culture conditions) was created to clearly demonstrate the impact of the tested dietary treatments. No feeds optimized for the rearing of the tench (Tinca tinca L. 1758) are available. Feeds are formulated to increase the growth rate or eliminate skeletal deformations. With the increasing prices of the basic components, fish meal (FM) and fish oil, poultry by-product meal (PBM) can be used. The aim of the study was to evaluate the effects of substitution of FM with PBM on the tench blood parameters, body composition and structure of skeletal muscles. Cage-reared female tenches (325 ± 18 g) were fed for 86 days with five types of feeds with 0% (control), 25.7%, 48.6%, 71.4% and 100% substitution of FM with PBM. No significant differences between the formulations were reported for weight, total length, fillet weight, visceral, liver, gonado-somatic, proximate composition and biochemical blood parameters. However, significant differences were found in the fillet profiles of fatty acids—an increase in the PBM content correlated with an increase in saturated and monounsaturated fatty acids and a decrease in n-3 PUFA and, generally, n-6 PUFA. Significant differences were also observed in, for example, the content of intramuscular fatty tissue and the level of organ lipidosis between the control variant (0% PBM) and that with 100% substitution. A sensory assessment indicated a higher gustatory value of the fillets in the case of feeds with 48.6% and 71.4% substitution.

Summary The activity of antioxidant enzymes [superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT) and glutathione-S-transferase (GST)] in the liver and gills of tench (Tinca tinca L.) from distinct habitats were studied. Fish were collected in the same season from three different water bodies: a cage culture supplied with cooling water from a power plant; traditional aquaculture in fishponds; and from the Odra River estuary. In all water bodies, the activity of antioxidant enzymes was significantly higher in the liver than in the gills. The highest activities of GST in the liver and GPx in the gills were detected in tench from the Odra River estuary, which may suggest abiotic stress connected with water quality in the estuary.