Effect of temperature and oxygen regime on growth and physiology of juvenile Salvelinus fontinalis × Salvelinus alpinus hybrids

Abstract

Effect of oxygen saturation and thermal regimes on growth and selected physiological indicators of juvenile Salvelinus fontinalis × Salvelinus alpinus hybrids were investigated in separate experiments. Hybrid status of tested fish, with S. fontinalis as the maternal species, was confirmed by sequence analysis. During both experiments fish doubled their initial weight in most tested groups. In experiment 1, fish (n = 516, 70.6 ± 1.5 g) were exposed to one of four oxygen regimes (normal, hyperoxic, 12 h alternating normal/hyperoxic, and 24 h alternating normal/hyperoxic) in triplicate (12 rearing tanks of four separate RAS) for 63 days. More favourable growth parameters were observed under normoxic conditions (85–95%) in comparison with hyperoxia (120–130%). Oxygen saturation was not associated with final feed conversion ratio, size variation, condition factor, selected somatic indices, or overall mortality rate. Oxygen saturation was significantly positively associated with leukocyte count and negatively associated with mean corpuscular haemoglobin concentration. Gills showed slight to moderate atypia in groups exposed to hyperoxia compared to the normoxia group. In experiment 2, fish (n = 560, 21.7 ± 0.3 g) were held in 7, 10, 13, or 16 °C water in four repetitions (16 rearing tanks of four separate RAS) for an 84-day period. Selected growth parameters were significantly higher at 13 °C than at 7, 10, and 16 °C. Feed conversion ratio was the lowest at 13 and 16 °C. Size variation and somatic indices exhibited no differences among treatments, while condition factor was significantly higher at 10 and 13 °C. Mortality rate increased from 1.4% to 30.5% with rise in temperature, with highest mortality recorded at 16 °C. Hyperoxia showed no advantage on growth of tested hybrids, while 13 °C was optimal water temperature for their culture.