THE DIGESTIVE PHYSIOLOGY OF HERBIVOROUS, OMNIVOROUS AND CARNIVOROUS CRUSTACEAN LARVAE - A REVIEW

While most copepods are holoplanktonic, decapod larvae are meroplankto nic with a pelagic larval development ranging from days (Penaeidae) to weeks (most Palaemonidae, Palinuridae). Reproductive strategies resul t in either the early release of larvae in large numbers of small plan ktonic forms (Penaeidae) or smaller numbers of advanced larvae after p arental incubation (Brachyura, Palaemonidae, Nephropidae, Palinuridae) . Commercially-cultured decapod larvae exhibit a wide range of feeding strategies exploiting most of the trophic levels found within the pla nktonic ecosystem. Studies on these crustacean larvae demonstrate how their digestive physiology is adapted to different feeding strategies during larval development, and provide an insight into the design of a ppropriate artificial feeds for commercial culture. Comparative measur ements of digestive enzyme levels reveal that trypsin-like protease ap pears to dominate in all larvae investigated. Highest levels occur in herbivorous penaeid and brachyuran larval stages. In contrast, carnivo rous lobster and caridean larvae show low protease activity at first f eeding and appear to rely upon high-energy digestible live prey for th eir nutrition. Ontogenetic changes in enzyme type, activity and conten t are displayed during the penaeid mysis and caridean, brachyuran late zoeal stages as larvae transfer to higher trophic levels. The range a nd extent of these changes are reviewed for the commercial larval grou ps of commercially important species. (C) 1997 Elsevier Science B.V.