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 comp arisons of visual appearance, dry weight and carbon and nitrogen conte nt of fresh food organisms with material recovered from faeces. Visual ly, the degree of digestion of food particles ranged from no discernib le change of lamellibranch larvae, cope-pod eggs, intact copepod faeca l pellets and some phytoplankton species, to varying degrees of remova l of body constituents in copepods, cladocerans and decapod zoea. For crustaceans, the proportion of body constituents removed was related t o the size and construction of their apparently indigestible exoskelet on. Upon defaecation larger organisms showed the greatest percentage l oss in dry weight and carbon. A high percentage of nitrogen was extrac ted from all organisms. There was no consistent difference in digestiv e efficiency between different age groups of larvae.