Effects of photoperiod and light intensity on growth and activity of juvenile haddock ( Melanogrammus aeglefinus)

Abstract

Enhancement of growth of juvenile haddock ( Melanogrammus aeglefinus) was achieved through photomanipulation. After 24 weeks (August–January), hatchery-reared haddock under 24 h light were 53–60% heavier than those under natural photoperiod. In a second 24-week experiment, haddock were grown under five photoperiod regimes (natural photoperiod, 12, 16, 20 and 24 h light) with two light intensities (30 and 100 lx) at 24 h. Continuous light (and 20 h light) resulted in the greatest growth response, though other seasonally unchanging photoperiods (12 and 16 h light) also resulted in faster growth than natural photoperiod. Reduced light intensity, from 100 to 30 lx, at 24 h, led to a further 11% improvement in body mass. The effects of photomanipulation declined as temperatures decreased in late autumn and winter. Locomotor activity was the greatest under natural photoperiod (100 lx), less at 24 h (100 lx) and lowest at 24 h (30 lx). Lower swimming activity under continuous dim light may translate into metabolic savings and increased body mass. Integrating these findings with research on larval haddock suggests a period in the ontogeny exists during which bright light should be dimmed to maximize growth and this perhaps coincides with changes in body morphology and behaviour associated with benthic foraging.