DIGESTIVE ENZYMES IN PARALARVAL CEPHALOPODS

摘要

Fourteen enzymes involved in digestion (esterases, glycosidases and peptidases) were localized by histochemical methods in planktonic paralarvae belonging to four families of cephalopods: Octopodidae, Bolitaenidae (Octopods), Ommastrephidae and Enoploteuthidae (Oegopsid squids). The high protease activity and very low or histochemically undetectable amylasic activity indicate a carnivorous diet suggesting that the diet of paralarvae resembles that of adults. The digestive gland displays the highest enzyme activities which agrees with the key role of the gland in the digestive processes of cephalopods. In particular, the gland appears to be the main source of the proteolytic enzymes found in the posterior digestive tract. The high acid phosphatase activity, DAP II and acetyl-glycosaminidase activities, typically lysosomal, point to intracellular digestive processes in the gland. The posterior salivary glands are as well developed in squids as in octopods and they display several enzyme activities, most notably a high proteolytic activity. This could indicate that the salivary glands would be more involved in the digestive processes in paralarval squids than in adults where they are mostly poison glands. In all of the specimens studied, the whole digestive system appears to be already developed and able to digest prey. The high level of alkaline phosphatase activity of the skin suggests active exchanges with the external medium. It seems possible therefore that nutrients could be absorbed through the skin and provide a part of the energy necessary to the young cephalopods.