However, 31.2% showed resistance to cotrimaxasole, 91.6% to sulphafurazole and 65.8% to sulphadiazine (Otta, 1997).

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4 416 I. Karunasagar, S. K. Otta et al. (1994) reported mass mortality of P. monodon larvae due to chloramphenicol resistant strains of V. harveyi. Later studies showed that V harveyi is capable of forming biofilm on various surfaces and that such biofilm bacteria are resistant to treatment with water sanitisers such as chlorine and iodophors (Karunasagar et al., 1996). Thus it is possible that biofilm formation by Vibrio spp. in the hatchery environment contributes to their persistence in the system. Though antibiotics are often used in hatcheries, the recent survey of antibiogram of bacterial isolates from hatchery systems in India indicated that 97.6% were sensitive to chloramphenicol and 97.3% were sensitive to tetracycline. However, 31.2% showed resistance to cotrimaxasole, 91.6% to sulphafurazole and 65.8% to sulphadiazine (Otta, 1997). and I. Karunasagar Table 4. Incidence of MBV monodon larvae west in apparently obtained from healthy hatcheries Penaeus in south coast of India Monodon baculovirus infection Mass mortalities in P. monodon larvae due to infection with monodonbaculovirus (MBV) in India has been reported by Ramasamy et al. (1995). They recorded 81% prevalence of MBV in post larvae in east coast of India with infected PL showing 90% mortality. However, our studies on the west coast of India suggest that occlusion bodies indicative of MBV could be detected in 83% of apparently healthy larval batches tested (Table 4). Examination of fecal pellets from brood stock using malachite green showed the presence of MBV occlusion bodies (Fig. 1). MBV infection is very common in many parts of Indo-Pacific region. Many authors (Baticados et al., 1992; Flegel et al., 1992; Lightner et al., 1992) have recorded incidence ranging from 7080% in various hatcheries in Thailand, The Philippines, Indonesia and Taiwan and have suggested that MBV is not a highly virulent pathogen of P. monodon. Our observations suggest that the situation is similar with respect to P. monodon cultured in India. Fig. 1. Malachite from Disease problems affecting shrimp in grow-out ponds Monodon baculovirus infection Until the middle of 1994, there had been no major instances of mass moralities in cultured shrimp in India. The first sign of problem with viral disease of shrimp was noticed in Gudur, Andhra Pradesh along east coast of India during July 1994 where mass mortality was noticed in all the farms along the creek. All age groups of P. monodon were affected but P. indicus was not. Moribund shrimps had no external signs except reddishness of hepatopancreas. Histological examination of sion green Penaeus bodies stained monodon of MBV (Bar: preparation of fecal sample brood showing occlu- stock 10 Đm). shrimps from a few farms indicated presence of eosinophilic intranuclear occlusion bodies suggestive of MBV (Karunasagar et al., 1998). Moribund shrimp had high bacterial counts (around 106/m/) in hemolymph indicating septicaemia. Though the findings suggest MBV infection and bacterial septicaemia, rapid mortality (100% mortality in 2-3 days) suggested the possibility that another virus was also involved in this outbreak. Earlier studies (Anderson et al., 1987; Chen et al., 1989;

5 Shrimp diseases Lightner et al.,1987; Nash et al., 1988) indicated that MBV is generally found in mixed infection with other pathogens including viruses, bacteria or parasites. Table 5 gives a list of viral diseases of shrimpreported from India. Vijayan et al. (1995) noted that the prevalence ranged from 11-42% in various ponds in southeast coast of India. Interestingly, they noticed the incidence of MBV even in P. indicus. However, they did not notice mortality in any of the ponds. In our study along the south west coast of India, we had one case of mortality of P.monodon in a semi-intensive type of culture pond (stocking density 10/m2) which was associatedwith MBV infection. The shrimps were 1012 g in size and examination of hepatopancreas showed intranuclear occlusion bodies both in malachite green preparation and histopathological sections (Fig. 2). Hemolymph of infected shrimp had bacterial counts ranging from cfu/ml and the bacterial species Fig. Table 5. Viral 2. HE stained diseases histopathological hepatopancreas (Bar: of shrimp 10 Đm). showing reported section occlusion from India of P. monodon bodies of MBV in India 417 encountered were V.alginolyticus, V.parahaemolyticus, V harveyi and Pseudomonas sp. The shrimps also had epibionts such as Zoothamnium sp. and Epistylis sp. on the shells as well as gills. This is consistent with the observation of others (Anderson et al., 1987; Chen et al., 1989; Lightner et al., 1987; Nash et al., 1988) that MBV is generallyfound in mixed infections. Sundararaj et al. (1995) reported an outbreak of MBV infection in a farm in south east coast of India with a mortality of 3050 percent. The results of this study show that though the incidence of MBV in P.monodon larvae is high, they do not cause serious problems in grow-out systems. This is in agreement with the theory that MBV is well tolerated by shrimpif other cultureconditions are optimal (Lightner et al., 1987; Fegan et al., 1991). The situation with respect to MBV in India is similar to what has been reported in other south east Asian countries (Baticados et al., 1991; Flegel et al., 1992; Lightner et al., 1992). Whitespot syndrome During white spot syndrome caused severe mortalities of cultured shrimp P. monodon and P. indicus along east coast of India (Anon, 1995). The loss has been estimated (Alagarswami, 1995) to be about 10,00012,000 tons valued at Rs billion (1 US$ = Rs. 38.0). This disease has also spread to the west coast and has caused serious mortalities (Karunasagar et al., 1997). How this virus (white spot baculovirus: WSBV) came to India is debated. Before the outbreak occurred in India, this virus has been reported to cause mortalities in P. japonicus in Japan (Momoyama et al., 1994), Taiwan (Chou et al., 1995) and this virus was detected in P. monodon in Thailand (Wongteerasupaya et al., 1995). One argument is that the virus came to India through clandestine import of nauplii. Prior to this outbreak, there was a severe shortage of seeds in India (Alagarswami, 1995). At present, white spot syndrome is considered a serious threat to the shrimp culture industry in India. When the disease broke out towards the end of 1994, a crop holiday was declared but when the culture resumed, the disease continued to cause mortalities in the farms. Since the farmers simply drain the infected ponds, the virus seems to have infected the natural stock of P. monodon. We have been able to detect histopathological changes indicative of WSBV infection (hypertrophied nuclei, intranuclear eosinophilic to basophilic inclusions) in wild stock of P. monodon, P. indicus, P. merguiensis and crabs. Thus there seems to he a natural reservoir of infection and this

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