FAO official common names: Fr - Crevette géante tigrée; Es - Langostino jumbo
Taxonomic and biological features
Distribution The giant tiger prawn (Figures 1,2,3), Penaeus monodon, is found in the Indian Ocean and western Pacific (Indo-West Pacific) (FAO, 1970, 1980) and is distributed from east and southeast Africa to northern and eastern Australia, Japan, Pakistan and the Malay Archipelago (Dore and Frimodt, 1987; FAO, 1980). It is cultured commercially in much of its range. Western Indian Ocean and western Pacific populations have separate evolutionary histories (Duda and Palumbi, 1999).
Habitat and behavior Penaeus monodon is found at depths from 0 to 110 m, inhabiting bottom mud and sand. Giant tiger prawn live in brackish, estuarine (juveniles) and marine (adults) environments (FAO, 1980). In its natural range, P. monodon frequents water temperatures of 18–34.5 oC and salinities of 5–45 ppt (Branford, 1981; Chen, 1990). It is even grown commercially at salinities of 1–5 ppt (Musig and Boonnom, 1998). Penaeus monodon appears to select muddy mangrove channels and often associates with marginal or floating vegetation (de Freitas, 1986).
Marine shrimp life cycle The life history of P. monodon (Figure 4) has an offshore planktonic larval phase of about 14 (Silas et al., 1978) to 20 days (Kenway and Hall, 2002); an estuarine, benthic postlarval and juvenile phase of over 6 months (33 g); a coastal subadult phase of 5 to 6 months (60 g); and an inshore and offshore ocean adult and spawning phase (60 to 261 g) (Dall et al., 1990, Kenway and Hall, 2002). Mating between a recently moulted (soft-shelled) female and a hard-shelled, smaller male occurs at night in the ocean (Hudinaga, 1942). Adult P. monodon are found in offshore waters on sandy bottom at depths of 20–40 m. The larvae move towards the coast, entering estuaries and mangrove swamps that serve as nursery grounds. They then migrate to deeper water when they become adolescent. Penaeus monodon has six nonfeeding naupliar stages, three protozoeal stages and three mysis stages (FAO, 1985a).
Morphological characteristics Penaeus monodon are generally dark coloured, with the carapace and abdomen transversely banded with black and white (Figures 1,2,3,5). The rest of the body is variable, ranging from light brown to blue or red, while some smaller specimens show a dull red dorsal strip from the rostrum to the sixth abdominal segment (Grey, Dall and Baker, 1983).
A = antenna, AB = abdominal segment, AC = adrostral carina, AF = antennular flagellum, AS = antennal scale, E = eyestalk, HS = hepatic spine, P = pereiopods, Pl = pleopods, R = rostrum, SAS = sixth abdominal segment, T = telson, TM = third maxilliped, U = uropod.
This is the largest commercially available shrimp, reaching 330 mm or more (Dore and Frimodt, 1987), with a maximum total length of 336 mm (Figure 6). Sexually mature males (with spermatophores) can be found from about 33 g body weight (BW) (37 mm carapace length (CL), 134 mm total length (TL)), while the females sometimes have spermatophores in their thelycum from 60 g BW (47 mm CL, 164 mm TL). Most females mature at a slightly larger size, around 82–97 g BW (180–190 mm TL) (Kenway and Hall, 2002). Shrimp have an exoskeleton (the "shell") that is periodically shed (moulted) to allow further growth. The head is called the thorax, and the tail (or abdomen) has six segments. The last abdominal segment is the telson, which allows the shrimp to kick or jump backwards when the tail is rapidly flexed in an escape reflex. The thorax has a spine called the rostrum, one pair of eyes, two pairs of antennae, three pairs of maxillipeds for feeding and five pairs of walking legs. Each abdominal segment except the telson has a pair of fins called pleopods on the ventral side. Shrimp use the pleopods for forward swimming. The morphological features most widely used in taxonomic differentiation of members for the Superfamily Penaeoidea are the rostrum, carapace, antennular flagella, scaphocerite, third maxilliped, pereiopods, abdomen, telson and the male and female genitalia, as well as the appendix masculina in the male (de Freitas, 1987).
The rostrum of P. monodon has 7 or 8 dorsal and 2–4 (occasionally 5) ventral teeth (Holtuis, 1949; Perez Farfante and Kensley, 1997) (Figures 5, 7). Males are identified by a petasma. Males produce spermatophores that lack attachment structures and contain the sperm (Perez Farfante and Kensley, 1997). The female thelycum is closed (Perez Farfante and Kensley, 1997) (Figure 8).
Shrimp eggs hatch within 15 h (temperature dependent) as a nonfeeding nauplius stage (Figure 9) that undergoes six moults (Moto, 1979) over 50 h. The next three metamorphoses are the protozoea stages (FAO, 1985a) (Figure 10). Protozoea I (zoea I) has compound eyes under the carapace that are thus not clearly visible; zoea II has a pair of stalked compound eyes and zoea III has a pair of biramous uropods (Motoh, 1979). After 4–6 d, the protozoea finally metamorphoses into a mysis. There are three mysis stages over 3–4 d. The mysis remain drifting in the water and metamorphose into postlarvae (Motoh and Buri, 1981).
Reproduction Wild males produce spermatozoa from around 35 g BW and females becomes gravid from 70 g. Mating occurs at night, shortly after moulting, while the cuticle is still soft, and sperm are subsequently kept in a spermatophore (sac) inserted inside the closed thelycum of the female. Females of P. monodon (Figure 11 and 12) are highly fecund, with gravid individuals producing as many as 500 000 to 750 000 eggs. Spawning occurs at night and fertilization is external, with females releasing sperm from the thelycum as eggs are released in offshore waters. Nauplii hatch 12–15 h after fertilization (FAO, 1985a).
