Low light intensity can reduce Atlantic salmon smolt quality

The objective of this study has been to investigate the effect of light intensity (10, 21, 43, 200 and 650lx) during smolting and its potential influence on gill Na+,K+-ATPase (NKA) activity, endocrinology, ion regulation, growth, morphology, and spinal development in Atlantic salmon. Gill Na+,K+-ATPase activity, plasma glucose and blood PCO2 were all affected by time (study duration 176days), while no differences were seen as a result of the different light intensity treatments. Growth rate was positively correlated to light intensity. Lower body silvering index, reduced fin area (5–7% lower in the 10 and 21lux groups) and increased percentage of skeletal abnormalities (6.9% in the 10lux group vs. 1% in the 650lux group) at low light intensity were seen. In a second experiment juvenile Atlantic salmon parr were reared in August at LD12:12, at either 1lx or 1000lx and circulating plasma thyroxin (FT) levels measured. Plasma FT4 levels remained low in the low light intensity group (1lx), whereas FT4 levels increased significantly from 2 to 5h in the high intensity group (1000lx). Total T4 levels were nearly 2-fold higher 5h after lights-on in the high intensity group compared with the low. Overall, the present data suggests that a minimum light intensity of 43lx is needed to secure optimal smolt quality, development, welfare and growth in Atlantic salmon.