Effects of temperature on body chemical composition and incidence of deformities in juvenile tench, Tinca tinca (Actinopterygii: Cypriniformes: Cyprinidae), fed a commercial dry diet and/or natural food

Background. Water temperature is a major factor regulating fish metabolism. It can influence body chemical composition and the incidence of body deformities. The latter often develop in farmed fish and this issue is currently emerging as a serious problem for aquaculture. Determining the effects of water temperature on body chemical composition and fish body deformities is an important subject for research in fish biology and nutrition, and aquaculture. The presently reported study was conducted using juvenile tench, Tinca tinca (Linnaeus, 1758), an important aquaculture species in Europe. Two hypotheses were tested: 1) temperature can significantly influence body chemical composition and the incidence of body deformities in fish; 2) the effects of temperature on fish depend on their diet. Materials and methods. Fish, with an initial total length of 28.4 ± 2.7 mm and body weight of 0.24 ± 0.07 g, were reared at 20, 23, and 26°C and fed dry feed Aller Futura (Aller Aqua, Denmark) only, or a combination of this feed and natural food (frozen larvae of Chironomidae) in a 3 ÷ 2 ratio of dry matter, or the natural food alone. The duration of the experiment and the daily food rations were adjusted to the experimental temperatures based on a correction factor, q, of 1.000, 0.779, or 0.609, respectively. The experiment duration was 92, 72, or 56 days for the respective temperatures. Results. Body deformities occurred in all groups of fish fed solely or partially with the dry diet (21.5%–89.5%). The incidence of deformities was directly proportional to the temperature and the content of dry feed in the diet reaching the maximum in fish fed exclusively the dry diet at 26°C. Water temperature and fish diet influenced body chemical parameters (moisture, protein, lipid, ash, Ca, P, Mg, Ca ÷ P, Mg ÷ P), but water temperature did not have a significant effect on whole-body P content. Conclusion. Water temperature proved to significantly influence fish chemical body composition and the incidence of body deformities in fish fed dry diet. The major factor that caused fish P deficiency, and resulted in low body ash content and body deformities, was insufficient bioavailability of P in the dry diet. Water temperature appeared to only modify P deficiency symptoms in fish.