Temperature influence on key players of the somatotropic axis of tench, Tinca tinca (Actinopterygii: Cypriniformes: Cyprinidae)
Background. Tench, Tinca tinca (Linnaeus, 1758), has been cultivated in Polish fish farms since centuries, due to its good quality meat. However, the most critical problem in tench culture is the slow growth, which makes farming of this species unprofitable. Growth rates of fish are influenced by numerous internal and external factors such as water temperature, food availability and quality, as well as photoperiod. In order to analyse and improve tench growth rate, the most important factors (GH, IGF-I) of the somatotropic axis should be analysed against selected culture factors. Key elements of the axis play a pivotal role in the coordination of protein and energy metabolism during postnatal growth. Therefore, the aim of this study was to assess effect of water temperature on the activity of somatotropic axis of tench. Obtained results can be useful in tench farming in order to deal with mass gain. Materials and Methods. Forty tench, approximately 3+ years of age, were placed in eight 240 L tanks, five fish in each tank. There were four temperature regimes (10°C, 15°C, 20°C, and 25°C) studied separately for males and females during a period of one week. At the end of the experiment, 2 mL of blood, the whole pituitary gland, 2 liver samples, and one muscle sample were collected from selected fish specimens. Real-time PCR was used to assess the effect of water temperatures on the level of tench mRNA gh transcripts in pituitary-, liver-, and muscle samples. Also, the concentration of growth hormone (GH) protein was measured in relation to individual temperature treatments in blood plasma and liver samples using ELISA assay. Results. The highest cycle threshold (Ct) values of mRNA gh were detected in the pituitary samples. ELISA assays confirmed that water temperature affected GH and IGF-I concentrations in the blood and the liver samples. Additionally, results from ELISA assays confirmed sex size dimorphism (SSD) phenomenon in tench. Conclusion. Presented results shed new light on mechanisms of functioning of tench somatotropic axis and constitute benchmark information for future experiments on nutritional factors.