Effects of light spectrum on growth and stress response of rainbow trout Oncorhynchus mykiss reared under recirculating system conditions

Fish growth and physiology may be affected by light spectrum, which can be easily manipulated in indoor aquaculture facilities, and especially recirculating water systems, with little cost. Since data related to light spectrum and widely reared fish are still few, the present study aimed to investigate the effects of coloured light on growth performance and stress response to confinement of rainbow trout Oncorhynchus mykiss. Fish (145.3 ± 1.5 g) were reared under white (full spectrum, fluorescent lamps), red (605 nm) and blue (480 nm) light (lamps covered with appropriate filters) for 111 days under recirculating water systems (150 lx, 12L-12D). At the end of the experimental period and for each light treatment, fish were either subjected for 1 h to confinement stress or remained undisturbed (control groups). Total length of the fish reared under red light was greater than that of the other regimes, whereas other growth parameters showed a similar trend but were not significantly different from one another. Carcass proximate composition was not affected by light spectrum. Fish exposed to confinement showed typical primary (high cortisol) and secondary (high glucose and haematocrit, liver lipid mobilization, osmotic and ionic disturbances, blood acidosis, etc.) stress responses. Nevertheless, in fish reared under blue light, stress-induced cortisol increase was lower and liver lipids mobilization was absent compared with white light (significant interaction). Present results indicate that if stressors are kept to a minimum then red light could be suggested for the intensive rearing of rainbow trout.