Indian Council of Agricultural Research
CENTRAL MARINE FISHERIES RESEARCH INSTITUTE
CENTRAL MARINE FISHERIES RESEARCH INSTITUTE
Oxytetracycline (OTC) is a widely used antibiotic in both freshwater and marine intensive aquaculture practices. Responsible use of antibiotics requires data on in vitro efficacy against pathogens of targeted species, as well as on biosafety and tissue residue level in each targeted host. Accordingly, experiments were designed to evaluate the biosafety and tissue residue level of OTC in a marine aquaculture candidate species, viz., snubnose pompano (Trachinotus blochii). Biosafety of OTC was assessed by administration of medicated feed both at the therapeutic dose (80 mg/ kg biomass) and 3, 5, and 10 times the therapeutic dose. Exposure was done both for the rec- ommended duration of time (10 days) as well as two and three times higher than the recommended duration. Histological examination revealed moderate to severe tissue morphological changes in the liver, kidney, and gills of fish exposed to OTC. The liver was the first and most severely affected organ. Pathological effects in all the three selected organs were directly related to the dose and duration of OTC exposure. Further, tissue residue concentrations in the muscle of the group exposed to OTC at the therapeutic dosage for a duration of 10, 20, and 30-days were well below the maximum residual level prescribed by the European Commission and the US Food and Drug Administration, on day zero post-withdrawal, leaving its implications on consumer safety. Addition- ally, in vitro efficacy evaluation against marine fish pathogens of the target species, viz., Vibrio harveyi, Vibrio vulnificus, and Vibrio parahaemolyticus, showed that minimum inhibitory concentration and minimum bacteri- cidal concentration ranged from 0.6 to 1.5 ?g mL
To ensure reproductive success, sharks have adapted several strategies. It was observed that male sharks of Scoliodon laticaudus Müller & Henle, 1838 and Rhizoprionodon acutus (Rüppell, 1837) landed along a few centres of Gujarat coast, have highly calcified claspers which morphologically resembled ossified webbed foot. The morphological and anatomical study revealed that the terminal end of the clasper has been modified into an umbrella like organ called rhipidion which probably ensures that the clasper stays within the cloaca of the female until the sperm is delivered. The landed sharks were all mature. This recent observation of catch of many mature individuals near the coastal waters throws some light on the breeding season and breeding area of sharks along Gujarat coast. With episodes of extinction and threat to the existence of several species of sharks today, this reproductive adaptation of the sharks might helps them to survive and sustain adverse conditions.
The present study reports the taxonomic notes on Homolax megalops (Alcock 1894) off Kollam, Southeastern Arabian Sea. Homolax displayed close relationship with Paromola species, even though these were found to differ with respect to the length of pseudorostral spines. Additionally, the study documented the DNA sequences and genetic divergence between the genus Homolax and Homola (COI: 27.3%). Phylogenetic relationship of Homolidae with available 16S sequences from GenBank was also documented..
The present study describes a new species of myxosporean, Ellipsomyxa ariusi sp. nov., infecting the gallbladder of the threadfin sea catfish Arius arius (Hamilton, 1822). E. ariusi sp. nov. is characterized by bivalvular, ellipsoid or elongate-oval myxospores with smooth spore valves and a straight suture, arranged at an angle to the longitudinal spore axis. Mature myxospores measured 10.1 ± 0.8 µm in length, 6.8 ± 0.5 µm in width and 7.7 ± 0.7 µm in thickness. Polar capsules are equal in size and oval to pyriform in shape. They are positioned at an angle to the longitudinal myxospore axis and open in opposite directions. Polar capsules measured 2.8 ± 0.3 µm in length and 2.5 ± 0.4 µm in width; polar filaments formed 4-5 coils, and extended to 32.2 ± 2.1 µm in length. Monosporic and disporic plasmodial stages attached to the wall of gallbladder. Molecular analysis of the type specimen generated a 1703 bp partial SSU rDNA sequence (MN892546), which was identical to the isolates from 3 other locations. In phylogenetic analyses, genus Ellipsomyxa appeared monophyletic and E. ariusi sp. nov. occupied an independent position in maximum likelihood and Bayesian inference trees with high bootstrap values. The overall prevalence of infection was 54.8% and multiway ANOVA revealed that it varied significantly with location, year, season, sex and size of the fish host. Histopathological changes associated with E. ariusi sp. nov. infection included swelling, vacuolation and detachment of epithelial layer, reduced mucus production and altered consistency and colour of bile. Based on the morphologic, morphometric and molecular differences with known species of Ellipsomyxa, and considering differences in host and geographic locations, the present species is treated as new and the name Ellipsomyxa ariusi sp. nov. is proposed.
In the case of coinfections, multiple pathogens induce pathologies independently or in combination. The present study describes the pathological and microbiological characterization of Vibrio harveyi and two strains of Photobacterium damselae subsp. damselae causing coinfection in cobia reared in sea cages. All the isolated pathogens were virulent to juvenile cobia by injection challenge. The experimental challenge with the three isolated pathogens singly or in combination revealed a significant difference in the mortality profile. Lesions in natural coinfection consisted of ascites, fibrinous deposits on internal organs, and increased melanomacrophage centres (MMC) and extensive necrosis in kidneys. Lesions in experimental infection were limited to congestion of internal organs. Enzymatic activity of both extracellular products (ECP) and live cells by well diffusion showed the highest enzymatic index for gelatinase in the ECP of V. harveyi. The enzyme activity evaluated based on the API?ZYM system revealed the highest activity for alkaline and acid phosphatase in both ECP and bacteria. The MAR index indicated that the pathogens were from a low?risk region of antibiotic contamination.
Porcellana persica Haig, 1966 was collected from off the Kerala coast, Arabian Sea, India. This is the first record of both the genus and the species from Indian waters. The taxonomic characters are similar to the findings of Haig (1966), who described the species, and possibly this is the first detailed report on the species after her original description.
