Foraging behaviour of Atlantic cod (Gadus morhua) larvae in relation to prey concentration

Abstract

In spite of a tremendous amount of research on Atlantic cod (Gadus morhua) larvae, no information is available on the development of foraging behaviour over an extended period. We investigated the ontogeny of foraging behaviour of Atlantic cod larvae exposed to different prey concentrations from hatching to metamorphosis. The objective of this work was to determine if their foraging behaviour is influenced by prey concentration. Rotifers and (or) Artemia sp. were used as prey at concentrations of 0, 500, 1000, 2000, and 4000/L. During behavioural observations, which were carried out twice a week, foraging behaviour and activity of cod larvae were quantified. Larvae were sampled once a week and standard length and gut fullness were recorded. Larvae reared at concentrations of 1000 and 2000 prey/L swam significantly more but foraged (quantified by capture success) significantly less than the larvae reared at 4000 prey/L. Larvae reared at 4000 prey/L performed more orientations towards prey than larvae reared at all lower prey concentrations and the time spent per orientation increased from day 2 at all prey concentrations but declined as the larvae grew. However, this decline occurred earlier in larvae reared at 4000 prey/L than in larvae reared at other prey concentrations, and larvae reared at 4000 prey/L spent the shortest time per orientation at day 27 compared with day 34. Larvae reared at 4000 prey/L showed significantly higher success in capturing prey than larvae reared at all lower prey concentrations. After day 13 post hatch, larvae reared at 4000 prey/L were significantly greater in length than larvae reared at all other prey concentrations. Larvae reared at 0, 500, and 1000 prey/L did not survive beyond 11, 15, and 32 days, respectively, indicating that fewer than 2000 prey/L may not be adequate to keep cod larvae alive during intensive rearing. Our results suggest that the foraging behaviour of Atlantic cod larvae is influenced by prey concentration.