Protozoan parasites of the genus Perkinsus are considered important pathogens responsible for mass mortalities in many wild and farmed bivalve populations. The present study was initiated to screen populations of the Indian edible oyster Crassostrea madrasensis, a promising candidate for aquaculture along the Indian coasts, for the presence of Perkinsus spp. The study reports the presence of P. beihaiensis for the first time in C. madrasensis populations from the Indian subcontinent and south Asia. Samples collected from the east and west coasts of India were subjected to Ray's fluid thioglycollate medium (RFTM) culture and histology which indicated the presence of Perkinsus spp. PCR screening of the tissues using specific primers amplified the product specific to the genus Perkinsus. The taxonomic affinities of the parasites were determined by sequencing both internal transcribed spacer (ITS) and actin genes followed by basic local alignment search tool (BLAST) analysis. Analysis based on the ITS sequences showed 98 to 100% identity to Perkinsus spp. (P. beihaiensis and Brazilian Perkinsus sp.). The pairwise genetic distance values and phylogenetic analysis confirmed that 2 of the present samples belonged to the P. beihaiensis clade while the other 4 showed close affinities with the Brazilian Perkinsus sp. clade. The genetic divergence data, close affinity with the Brazilian Perkinsus sp., and co-existence with P. beihaiensis in the same host species in the same habitat show that the remaining 4 samples exhibit some degree of variation from P. beihaiensis. As expected, the sequencing of actin genes did not show any divergence among the samples studied. They probably could be intraspecific variants of P. beihaiensis having a separate lineage in the process of evolution. KEY WORDS: Edible oyster · Crassostrea madrasensis · Protozoan parasite · Perkinsus beihaiensis · Brazilian Perkinsus sp. · Indian subcontinent Resale or republication not permitted without written consent of the publisherDis Aquat Org 98: [209][210][211][212][213][214][215][216][217][218][219][220] 2012 zoospore. Transmission of Perkinsus spp. does not require an intermediate host. In moribund hosts or when cultured in Ray's fluid thioglycollate medium (RFTM), the mature trophozoites transform into hypnospores. In sea water, these hypnospores develop into zoosporangia, undergo zoosporulation and produce infective zoospores. Trophozoites and hypnospores are also infective .Since the introduction of molecular techniques in disease diagnosis, new species belonging to the genus Perkinsus have been described from various molluscan hosts across the world (Dungan & Reece 2006, Moss et al. 2008. Through culture in RFTM, the standard diagnostic method for Perkinsus spp., the parasites can be identified up to the genus level. The broad host range and highly variable and overlapping morphologic and morphometric features of these parasites makes their species-level identification difficult (Goggin & Lester 1995, Perkins 1996, Coss et al. 2001. ...

An outbreak of skin ulcers with morbidity and mortality rate of 80% and 20% respectively, among Genetically Improved Farmed Tilapia (GIFT) sub-adults reared in a brackish water floating cage farm of Kochi, Kerala, India was reported. Bacterial isolation attempts from various internal organs (blood, kidney, liver, spleen and brain) of different diseased fish indicated a common bacterial etiology. Organisms were identified as Vibrio vulnificus based on conventional microbiological methods followed by molecular confirmation. Additionally, V. vulnificus marker specific for fish virulence was present in the isolates. Fish pathogenicity was confirmed by challenge tests. LD 50 was calculated as 2.1 × 10 5.13 CFU/fish and 2.1 × 10 6.12 CFU/mL in injection and immersion route respectively. pilF polymorphism-based PCR and vvhA gene sequence indicated potential danger for humans. The strain was positive for siderophore, hemolysin, capsule, polar and lateral flagella. The strain could multiply rapidly in healthy fish serum. All these results indicated that the isolate could act as a primary pathogen for tilapia fish. Interestingly, serum survival ratio of the pathogen was significantly larger at higher temperatures (p ≤ .05); which may explain the increase in infective capacity of V. vulnificus at higher temperature. Multiple antibiotic resistance index of the strain was ≤0.2. In conclusion, the paper provides detailed descriptions of clinical signs, microscopic and macroscopic lesions of a natural disease outbreak among tilapia raised in brackish water cage farms of India. The concurrent attempts to identify and characterize the etiology fetches the basis for future development of effective control and preventive measures against V. vulnificus, the most infectious and lethal of all zoonotic vibrios.

The present study forms the first report of Nematopsis sp. infection in the edible oyster, Crassostrea madrasensis from India. The study was carried out as part of a detailed pathological investigation of C. madrasensis along the southwest coast of India. Sporozoites of Nematopsis sp. were found in samples collected from two locations. Light microscopic observation revealed ellipsoidal oocysts measuring 16.63±2.40 µm in length and 11.11± 2.49 µm in width (n=30) in the connective tissues of gills, mantle, visceral mass and gonads. Prevalence of infection ranged from 11 to 27%. Apparent pathological changes included compression of adjacent digestive diverticulae in visceral connective tissue infections and presence of phagocytosed oocysts in water channels in the case of gill infections. With relevance to the expanding culture of C. madrasensis, monitoring potential pathogens of this species in its natural habitat is important for developing suitable health management packages.

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Information on unintended effects of therapeutic exposure of antibiotics on the fish gut microbiome is a vital prerequisite for ensuring fish and environmental health during sustainable aquaculture production strategies. The present study forms the first report on the impact of florfenicol (FFC), a recommended antibiotic for aquaculture, on the gut microbiome of snubnose pompano (Trachinotus blochii), a high-value marine aquaculture candidate. Both culture-dependent and independent techniques were applied to identify the possible dysbiosis and restoration dynamics, pointing out the probable risks to the host and environment health. The results revealed the critical transient dysbiotic events in the taxonomic and functional metagenomic profiles and significant reductions in the bacterial load and diversity measures. More importantly, there was a complete restoration of gut microbiome density, diversity, functional metagenomic profiles, and taxonomic composition (up to class level) within 10–15 days of antibiotic withdrawal, establishing the required period for applying proper management measures to ensure animal and environment health, following FFC treatment. The observed transient increase in the relative abundance of opportunistic pathogens suggested the need to apply proper stress management measures and probiotics during the period. Simultaneously, the results demonstrated the inhibitory potential of FFC against marine pathogens (vibrios) and ampicillin-resistant microbes. The study pointed out the possible microbial signatures of stress in fish and possible probiotic microbes (Serratia sp., Methanobrevibacter sp., Acinetobacter sp., and Bacillus sp.) that can be explored to design fish health improvisation strategies. Strikingly, the therapeutic exposure of FFC neither caused any irreversible increase in antibiotic resistance nor promoted the FFC resistant microbes in the gut. The significant transient increase in the numbers of kanamycin-resistant bacteria and abundance of two multidrug resistance encoding genes (K03327 and K03585) in the treated fish gut during the initial 10 days post-withdrawal suggested the need for implementing proper aquaculture effluent processing measures during the period, thus, helps to reduce the spillover of antibiotic-resistant microbes from the gut of the treated fish to the environment. In brief, the paper generates interesting and first-hand insights on the implications of FFC treatment in the gut microbiome of a marine aquaculture candidate targeting its safe and efficient application in unavoidable circumstances. Implementation of mitigation strategies against the identified risks during the initial 15 days of withdrawal period is warranted to ensure cleaner and sustainable aquaculture production from aquatic animal and ecosystem health perspectives.

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The present case study provides an insight into the tissue level pathological alterations inflicted by Bucephalus sp. infections in the edible oyster, Crassostrea madrasensis. Oysters collected during a routine study (from the oyster beds along the Southeast coast of India during July 2012) was found to harbor larval bucephalid infection. Though the prevalence of infection was low (1.37%), the intensity of infection was high, rated as two on the semi-quantitative scale. Infected oyster did not exhibit any external manifestation, but the developing parasitic stages, after replacing the host gonadal tissues have further spread to the gills and digestive glands. Regions of gonadal tissues were found packed with slender, branching sporocysts containing germ balls and crecariae, destroying the acinar architecture of the gonads. Immune responses like encapsulation against the infective stages were totally absent. The altered acinar architecture and reduced volume of the gonadal acini appeared to be insufficient to support any gametic release, resulting in gonadal dysfunction leading to parasitic castration of the host. An increase in the prevalence of Bucephalus sp. infection in the ecosystem could seriously hamper the reproductive potential of the wild stocks of oysters, thereby affecting the viability of oyster farming in the region.