DIGESTION OF NATURAL FOOD BY LARVAL AND POSTLARVAL TURBOT SCOPHTHALMUS-MAXIMUS

The digestion of natural, mainly crustacean zooplankton, by different age groups of turbot Scophthalmus maximus larvae was evaluated by comparisons of visual appearance, dry weight and carbon and nitrogen content of fresh food organisms with material recovered from faeces. Visually, the degree of digestion of food particles ranged from no discernible change of lamellibranch larvae, cope-pod eggs, intact copepod faecal pellets and some phytoplankton species, to varying degrees of removal of body constituents in copepods, cladocerans and decapod zoea. For crustaceans, the proportion of body constituents removed was related to the size and construction of their apparently indigestible exoskeleton. Upon defaecation larger organisms showed the greatest percentage loss in dry weight and carbon. A high percentage of nitrogen was extracted from all organisms. There was no consistent difference in digestive efficiency between different age groups of larvae.