Introduction:
The application of artificial photoperiod has helped the salmon industry reduce the early maturation, enhance smoltification and growth. Artificial lighting seek to stimulate fish photoreceptors as pineal gland and retina. Regarding light perception, the intensity (quantity) and the spectral composition (quality) of light determine the physiological response of salmon (Bromage et al. 2001; Migaud et al. 2007; Vera et al. 2010). Changes in water quality can have profound effect on the transmission of light. In RAS experimental conditions NOFIMA researchers had observed differences in the absorbance of different wavelengths in RAS. The present study was conducted to determined if turbidity in RAS and sea cages farmed conditions there are changes in the spectral composition of the artificial lighting used in the photoperiod regimes on farmed Atlantic salmon.
The study was carried out in two commercial smolt RAS facilities with two different levels of turbidity (NTU) and in a sea site in two different days with two level of transparency measured by sechhi disc in the X region in Chile. In all the measurements the light source was a 650W multispectral (white spectrum with a blue and green pick) LED underwater luminaire. The underwater spectrum was register at different depths (Fig.1) using a hyperspectral radiometer (RAMSES G2, TriOS, Germany)
The results of this study demonstrated the light spectrum decomposition generated by the water turbidity, generating a selective penetration of the different wavelengths, particularly important in the blue end of the spectrum at the bottom of the culture units suggesting that there might be an effect of the fish photoreception. So, green lights might be the most suitable for RAS, even though we are still working on proving this in field conditions.