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We investigated mass mortalities of koi, Cyprinus carpio Linnaeus, 1758, experienced in South Indian fish farms by virus isolation, electron microscopy, PCR detection, sequencing of capsid protein gene and transmission studies. Samples of moribund koi brought to the laboratory suffered continuous mortality exhibiting swimming abnormalities, intermittent surfacing and skin darkening. Irido-like virus was isolated from the infected fish in the indigenous snakehead kidney cell line (SNKD2a). Icosahedral virus particles of 100 to 120 nm were observed in the infected cell cultures, budding from the cell membrane. Virus transmission and pathogenicity studies revealed that horizontal transmission occurred associated with mortality. PCR analysis of infected fish and cell cultures confirmed the presence of Ranavirus capsid protein sequences. Sequence analysis of the major capsid protein gene showed an identity of 99.9% to that of largemouth bass virus isolated from North America. Detection and successful isolation of this viral agent becomes the first record of isolation of a virus resembling Santee-Cooper Ranavirus from a koi and from India. We propose the name koi ranavirus to this agent.

Aims: To study the strain variability among Vibrio alginolyticus isolates from different sources by insertion sequence-targeted PCR fingerprinting and whole cell protein profile analysis. Methods and Results: Eleven strains of V. alginolyticus were isolated from seven different sources including healthy, infected, farm-reared and wild shrimps. Following biochemical characterization, the isolates were analysed by PCR fingerprinting and whole cell protein analysis by SDS-PAGE. The strains were genetically different irrespective of the sources of isolation. Conclusions: Strain variation exists in V. alginolyticus isolates obtained even from the same source, and PCR fingerprinting is a simple and efficient method in identifying strain-specific variations among the different isolates. Significance and Impact of the Study: Vibrio alginolyticus is implicated in severe vibriosis of marine aquaculture systems although many strains are avirulent and could be used as probiotic strains. As a wide variation exists among this species, differentiating the harmful and beneficial strains would help in finding ways of controlling the infections by eliminating harmful shrimp pathogenic vibrios.

The intensification of aquaculture has been unique in showing the overwhelming changes in global food production in the last 100 years. Presently, it is playing a vital role in the economies of several countries. Conversely, it is also to be noted that the progression of aquaculture has been the foundation of anthropogenic alteration of a gigantic hierarchy and hence not astonishingly, it resulted in spread and emergence of an increasing group of new unknown diseases. In India, Penaeus monodon, black tiger shrimp was previously the foremost-cultivated shrimp species. Subsequently in 2008, the American white leg shrimp Litopenaeus vannamei has effectively replaced it. The change in dominant species has affected disease concerns in India as well as in world shrimp aquaculture. White spot syndrome virus (WSSV) is the most deleterious for both species. Hepatopancreatic parvovirus (HPV), Monodon baculovirus (MBV) and Infectious hypodermal and hematopoietic necrosis virus (IHHNV) are the other significant infectious agents of P. monodon and L. vannamei. An emerging disease of loose shell syndrome (LSS) was already reported from India during late 1998. A more recent disease of L. vannamei in India is monodon slow growth syndrome (MSGS), a component of which seems to be Laem-Singh virus (LSNV). Thus, most of the information in this review relates to new emerging pathogens that threaten the cultivation shrimp industry in India.

To detect genomic variation of white spot syndrome virus (WSSV) isolates from different geographical regions of India, the variable number of the tandem repeat (VNTR) region of the ORF 94 (Thailand WSSV isolate - GeneBank Accession No. AF369029) was analysed using five specific sets of primers. Analysis of 70 WSSV-positive samples showed the presence of 14 different genotypes of WSSV with VNTRs ranging from 2 to 16 tandem repeats with the majority (85.47%) having 6-12 tandem repeats. Occurrence of different genotypes of WSSV was found to be neither correlated to any specific geographical region nor to the different growth stage of the tiger shrimp, Penaeus monodon. Pathogenicity studies conducted with 25 isolates of WSSV revealed the presence of virulent and avirulent strains of WSSV in Indian shrimp farms. However, an unambiguous link could not be established between the different genotypes and their virulence.