The digestive physiology of herbivorous, omnivorous and carnivorous crustacean larvae: a review.

While most copepods are holoplanktonic, decapod larvae are meroplanktonic with a pelagic larval development ranging from days (Penaeidae) to weeks (most Palaemonidae, Nephropidae) or months (some Palaemonidae, Palinuridae). Reproductive strategies result in either the early release of large numbers of small planktotrophic larvae (Penaeidae) or smaller numbers of advanced larvae after parental incubation (Brachyura, Palaemonidae, Nephropidae, Palinuridae). Hence it follows that commercially cultured decapod larvae exhibit a wide range of feeding strategies exploiting most of the trophic levels found within the planktonic ecosystem.

Studies on these crustacean larvae have demonstrated how their digestive physiology is adapted to different feeding strategies during larval development, and provide an insight into the design of appropriate feeds for commercial culture. Comparative measurements of digestive enzyme activity reveal that trypsin-like protease activity dominates in all larvae investigated, and that this is highest in herbivorous penaeid and brachyuran larval stages. In contrast carnivorous lobster and caridean larvae show low protease activity at first feeding and appear to rely upon high energy digestible live prey for their nutrition. Ontogenetic changes in enzyme type and activity level are displayed during the penaeid mysis, caridean and brachyuran late zoea 1 stages as the larvae transfer to higher trophic levels. The range and extent of these changes are reviewed for these commercial larval groups. Whilst it is possible to replace live feeds for herbivorous and some omnivorous larval stages, the replacement of Artemia nauplii as the major diet for genera such as Lysmata or Stenopus with a pelagic larval life extending over 100 days remains a challenge for the future.

(School of Ocean Sciences, University Wales Bangor, Menai Bridge, Gwynedd, N. Wales, UK)