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We report the results of controlled feeding trials on the tiger shrimp, Penaeus monodon (Fabricius). The desired colour was obtained by feeding a diet supplemented with astaxanthin (50 p.p.m) for 7± 8 weeks before harvest. Similar coloration was achieved, however, by including in the feed an algal material (Dunaliella salina) that contains bcarotene but no astaxanthin. Feed containing bcarotene at 125 p.p.m also gave the required coloration at 7±8 weeks, whereas the same results was obtained after only 5±6 weeks when feed containing 175 p.p.m b-carotene was used. Irrespective of whether the shrimp were fed astaxanthin or b-carotene, the main carotenoid accumulation was astaxanthin, in free and esteri®ed form, showing that P. monodon has the metabolic ability to convert b-carotene into astaxanthin. The supplementation with b-carotene or astaxanthin had no signi®cant effect on growth, average ®nal weight, survival rate or feed conversion ratio, nor on the immune response of the shrimp in terms of production of haemocytes phenoloxidase in the cytoplasmic granules of the haemocytes, microbial clearance ability and resistance to infectious diseases. This is a highly signi®cant development for commercial aquaculture, because it shows that supplementing diets with b-carotene can achieve the same result as doing so with much more expensive astaxanthin.

A¯atoxin B 1 was studied in juvenile black tiger shrimp (Penaeus monodon Fabricius) (1±2 g) to see the effects on growth performance and histopathology, and in adult shrimp (10±12 g) to study the effects on immuno-physiological function, histopathology and a¯atoxin residue. Feeds supplemented with 0, 50, 100, 500, 1000 and 2500 p.p.b. a¯atoxin B 1 were given to test groups for an 8-week period. A¯atoxin B 1 in the diet showed highly negative correlation to average weight, weight gain and survival (r = ± 0.99, ±0.96 and ±0.95 at P < 0.05, respectively)

Whlte spot syndrome virus (WSSV) is the cause of a widespread epizoot~c in cultured shrimp in Thailand and many other countries in Asia. A number of crustacean and other arthropod species have been proposed as reservoirs for the virus by feeding trials and PCR assays. Ho~vever, detailed histological studies are needed to confirm that suspected carriers have active viral infections. This study was carried out to determine whether 3 common crustacean residents of shrimp culture ponds (the sand crab Portunus pelagicus, the mud crab Scylla serrata, and krill Acetes sp.) could be experimentally infected with WSSV and, if so, what the effect of these infections would be. For krill, 3 routes of infection were tested (injection, ingestion and immersion) while for the crab species, only injection and ingestion were tested. WSSV preparations were made from naturally and experimentally infected Penaeus monodon as viral extracts from tissue homogenates (for injection and immersion) and as cut tissues (for ingestion). As determined by normal histology, electron microscopy and in situ DNA hybridization, all of the test species could be infected with M' SSV. For krill, injection was the most effective route (100% mortality in 3 d), followed by immersion (100% mortality in 5 d ) and ingestion (20% mortality in 9 d). For the crabs, injection was also the most effective route of infection. However, infection dld not necessarily lead to mortality. Mortality for injected sand crabs was 100% in 8 d but for mud crabs only 20% in 9 d . By ingestion exposure, there was no mortality for either species over the 9 d experimental period, even though infection was confirmed by histological examination. Based on the results of this study, the crab species and krill can be considered as viral reservoirs, since they are able to carry the infection and may persist for significant periods in the shrimp farming environment.

A new non-occluded baculo-like virus was detected from black tiger shrimp (Penaeus monodon) with yellow head disease in the southern part of Thailand. Virus particles observed in necrotic tissues of gills and lymphoid organ were bacilliform in shape, ranging from 150-200 nm in length and 40-50 nm in diameter, and were enveloped singly by a trilaminar unit membrane. From the experimental infection trials, it was assumed that this virus was the most virulent among the viruses which have been known in the black tiger shrimp, to date. Pathogenicity and some characters of the virus as well as pathological changes caused by this virus were described.

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