Natural larval diets
Shrimp nauplii are nonfeeding, photopositive planktonic stages. The nauplius feeds on yolk reserves deposited in the egg (Rothlisberg, 1998). The first three shrimp protozoeal stages are nonselective (opportunistic) filter-feeders (Rothlisberg, 1998; Narciso and Morais, 2001), typically feeding on phytoplankton and small zooplankton such as rotifers. From mysis through to PL, there is a transition to active predation on larger zooplankton (Lovett and Felder, 1990).
Juvenile diets
Penaeus indicus is omnivorous, feeding on bivalves, gastropods, amphipods (and other crustaceans), polychaetes, foraminiferans, plant tissues, detritus and diatoms (Table 1) (Panikkar, 1952; Gopalakrishnan, 1952; Panikkar and Menon, 1956; Hall, 1962; Angsupanich, Chiayvareesajja and Chandumpai, 1999). Juveniles seem to consume large quantities of algae (Panikkar and Menon, 1956). Larger specimens consume more crustaceans, including penaeids and brachyurans (Hall, 1962).
Digestive system
Detection of feed begins with sight and touch, but shrimp also have numerous chemoreceptors on various appendages that detect what is near them in the water. Appendages that function in chemoreception are the mandible, maxillule, maxilla, lateral antennular flagellum, dactyls of maxilliped 3 and periopods, merus of periopods, periopods, maxillipeds and the branchial chamber (Dall et al., 1990; Lee and Meyers, 1997). The digestive tract is divided into three main parts, the foregut, midgut and hindgut (Ceccaldi, 1997) (Figures 12 and 14). The foregut (proventriculus) comprises the oesophagus and a part of the stomach where mastication occurs. The midgut gland is made of blind tubules and is the area where digestive enzymes are secreted.
The shrimp mouth connects to the proventriculus via a short muscle-lined oesophagus. The mouth is associated with specialized feeding structures, the mandible, the paragnath (=labium), maxilla 1, maxilla 2, maxillipeds (1, 2 and 3) and a labrum that pushes bitten off pieces towards the mouth (Garm, 2004) (Figure 13). The mandibles possess both cutting and crushing processes and act to reduce food particle size. The second and third maxillipeds hold and pull the food.
