G. Nash

DNA fragment of Penaeus monodon baculovirus PmNOBII gives positive in situ hybridization with white-spot viral infections in six penaeid shrimp species

Abstract PmNOBII was first described from experimentally infected shrimp, but contemporary reports showed that white-spot virus infections in several penaeid shrimp species exhibited similar gross signs and histopathology. Using laboratory infected specimens of Penaeus monodon , DNA of the non-occluded baculovirus PmNOBII was extracted and digested with BamHI and EcoRI. Resulting DNA fragments were ligated with Bluescribe vector using T4 ligase and competent cells of Escherischia coli JM 107 were transformed. Two recombinant clones that gave negative hybridization with P. monodon DNA but positive hybridization with PmNOBII DNA were selected. Inserted DNA fragments of 0.9 kbp and 4.2 kbp were obtained from these clones after plasmid digestion with BamHI and EcoRI. These fragments were subsequently labeled with digoxygenin for visualization and tested using the in situ DNA hybridization technique with tissues from PmNOBII infected and non-infected laboratory shrimp. For viral infected nuclei identified by H and E staining in parallel samples, the 4.2 kbp fragment gave a stronger DNA hybridization signal than did the 0.9 kbp fragment. The 4.2 kbp fragment was then used for in situ DNA hybridization tests with commercially or experimentally cultivated shrimp specimens showing gross signs and histopathology characteristic of white-spot virus infection. Field signs of the disease included general reddish coloration, white granules of 1–2 mm under the cuticle and rapid mortality. Normal histology (H and E) revealed Cowdry-A type nuclear inclusions that developed to produce basophilic hypertrophied nuclei typical of PmNOBII, and transmission electron microscopy revealed characteristic rod shaped virions. All these specimens gave positive hybridization results, and included cultivated shrimp specimens of Penaeus chinensis, P. indicus, P. japonicus, P. merguiensis, P. monodon and P. vannamei obtained from various countries in Asia between August 1993 and January 1995. The data indicate that PmNOBII, or closely related variants, are currently responsible for a widespread epizootic in the Asian shrimp farming industry.

A preliminary study on the aerobic heterotrophic bacterial flora in giant freshwater prawn, Macrobrachium rosenbergii, hatcheries in Malaysia

Abstract A study was carried out to establish bacterial counts and the aerobic heterotrophic microflora in Macrobrachium rosenbergii hatcheries and larvae in Malaysia. Physicochemical characteristics, wet preparation pathology, and bacterial counts of larval culture tank water, tank sediment, tank surface, larval prawn surface, and washed larval tissue-slurries were determined for 15 larval cultures in three different hatcheries using a modified static “green water” or recirculating clear water rearing system. Tank water, tank sediment and washed larval tissue-slurry microflora was determined for six larval cultures. Sampled cultures ranged in age from 3 to 29 days. Physicochemical water characteristics fell within expected ranges. Thirteen of the larval cultures showed mild bacterial necrosis lesions at prevalences ranging from 2 to 64% of larvae samples examined. Total viable cell counts ranged from 3.7 × 103 to 5.6 × 106 per ml; 1.4 × 105 to 1.1 × 107 per ml; 2.7 × 103 to 5.1 × 105 per cm2; 1.4 × 101 to 5.7 × 105 per larva; and 0 to 2.0 × 105 per larva for the tank water, tank sediment, tank surface, larval surface and washed larval tissue-slurries respectively. Alcaligenes sp. and Vibrio sp. were the most frequently encountered genera. Alcaligenes sp., Bacillus sp., Plesiomonas sp., and Pasteurella sp. were the most abundant strains (prevalence > 10%) in tank water; Alcaligenes sp., Aeromonas sp., Vibrio sp., Plesiomonas sp., and Pasteurella sp., in tank sediment; and Vibrio sp., Alcaligenes sp., and Acinetobacter sp., in washed larval tissue-slurries.

Bacteriosis associated with epizootic in the giant sea perch, Lates calcarifer, and the estuarine grouper, Epinephelus tauvina, cage cultured in Malaysia

Abstract A mass mortality in marine cage-reared adult sea perch, Lates calcarifer , and grouper, Epinephelus tauvina , offshore Kukup Laut, State of Johore, southern Peninsular Malaysia was investigated. The quantity and quality of trash fish fed to the fish was determined to be inadequate and the water quality was reduced during the northeast monsoon occurring at this time. Histologically, affected fish presenting extensive multiple skin lesions demonstrated severe haemorrhagic ulcerative dermatitis with additional changes in the internal organs consistent with a subacute septicaemia and an underlying malnutrition. Pseudomonas sp., probably Pseudomonas anguilliseptica , was identified as the agent responsible for the haemorrhagic septicaemia in the fish. With the end of the northeast monsoon, improved nutrition and water quality eliminated the problem in the adult fish, emphasizing the secondary opportunistic role of Pseudomonas and the importance of primary stresses such as that caused by suboptimal nutrition and environment in the initiation of disease in fish.

Baculovirus infection in brackishwater pond cultured Penaeus monodon fabricius in Indonesia

Abstract Penaeus monodon-type baculovirus (MBV) was diagnosed for the first time in P. monodon reared in brackishwater ponds in Indonesia. Viral infection was associated with cumulative mortalities of greater than 90% 2 weeks after the appearance of the clinical signs. Histologically, the hepatopancreata displayed a range of changes characteristic of MBV infection. This new outbreak of MBV emphasizes the need for the implementation of routine diagnostic and quarantine procedures in prawn disease control programmes.