Abstract
Even small changes in light intensity and spectral composition can have significant effects on the feeding rate, survivorship and growth of marine organisms. For fishes that can perceive them, ultraviolet-A radiation (320–400 nm, UVA) and polarized (POL) light purportedly increase the visibility of prey by enhancing target contrast. Consequently, the efficiency of prey location and ingestion (and, therefore, growth) should be higher in environments rich in UVA and/or POL light. We tested this hypothesis in growth rate experiments with larvae of Atlantic cod ( Gadus morhua), turbot ( Scophthalmus maximus) and Atlantic herring ( Clupea harengus). Turbot larvae possess an UVA-sensitive retinal photoreceptor, while cod and herring larvae apparently do not. Cod, turbot and herring larvae were reared in intensive culture – for at least 18 to 35 d from first-feeding – in 45 l optically isolated matt-black tanks under four light conditions: UVA + POL; UVA + DIFFUSE; NOUVA + POL; NOUVA + DIFFUSE. All light environments were matched for photon flux. There were five replicates per light exposure treatment and larvae were sampled every 3 to 5 d for dry weight. There was no significant difference in growth for any of the larvae under any of the light treatment conditions. These results indicate that, for these species, neither UVA nor POL light significantly improves growth rate in typical intensive culture systems.
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