Decapod crustaceans are among the most commercially important invertebrates. Larval, postlarval, or adult stages of several species of decapods may be found in large numbers in estuaries and rocky intertidal habitats near the shore, where they are vulnerable to various types of discharges. Because of their phylogenetic relationship to insects, and because pesticides often are applied in watersheds draining to estuaries, using decapods in pesticide toxicity testing is particularly relevant. Postlarvae of penaeid shrimp use the estuaries as nursery grounds until they are large enough to migrate offshore. Early life stages are particularly vulnerable.
Considerable diversity exists among decapods, which include shrimp, prawns, crabs, lobsters, and crayfish. They are classified into the suborders Pleocyemata or Dendrobranchiata, depending on whether they brood eggs or release them in water, respectively. Although there are exceptions and variations, shrimp are generally planktivores, whereas lobsters and crabs are predators and scavengers. Decapods share similarities at the larval and postlarval stages, when zooplankton is the primary food. Laboratory holding and testing is easier at these early stages because brine shrimp (Artemia salina) nauplii usually are an appropriate food.