Pathogenesis of Aeromonas caviae in Clariasmagur.

Aeromonas spp. is a pathogenic bacteria that potentially cause infection in farmed fish, including Catfishes. In the present study, dominant bacteria were isolated from diseased Clarias magur and tentatively named BLBM-05. Based on morphological, physiological, and biochemical features as well as 16S rRNA gene sequence and gyrB gene sequences (Gen Bank accession number: MT973994.1 and MZ398017.1), the bacteria in the isolate was found to be Aeromonas caviae. Further, the isolate was screened for five known virulence genes, namely ß-hemolysin, lafA, exu, ompA1 and ascV. Among them, three virulence genes related to pathogenicity, including aerolysin (aer), outer membrane protein (ompA1), lateral flagella (lafA), were identified in the A. caviae isolate. The median lethal dosage (LD50) of the BLBM-05 isolate for magur was determined as 1.53x106 CFU/mL. The histopathological analysis showed that the BLBM-05 isolate induced considerable histological lesions in the magur fish, including necrosis, hemolysis of erythrocytes, myolysis, hemorrhage, and desquamation in the intestinal tissue, tissue loosening, and infiltration of inflammatory cells. Drug sensitivity test showed that the isolate was susceptible to Gentamicin, Ceftazidine, Ceftrioxone, Amikacin, Tetracycline, Meropener and Oxytetracycline. The present results provide a scientific basis to identify A. caviae further, a line of treatment for magur infected by this pathogen.

Evaluation of alternative methods for estimating the precision of REML-based estimates of variance components and heritability.

Residual Maximum Likelihood (REML) analysis is the most widely used method to estimate variance components and heritability. This method is based on large sample theory under the assumption that the parameter estimates are asymptotically multivariate normally distributed with covariance matrix given by the inverse of the information matrix. Hence, these sampling variances could be biased if the assumption of asymptotic approximation is incorrect, especially when the sample size is small. Though it is difficult to assess the impact of sample size, an alternative option is to generate a full distribution of the parameters to determine the uncertainty of estimates. In this study, we compared the REML estimates of variance components, heritability and sampling variances of body-weight (BW), body-depth (BD), and condition-factor (K) with those obtained from four sampling-based methods viz., parametric and nonparametric bootstrap, asymptotic sampling and Bayesian estimation. The aim was to understand if a sample size of order 1413 was sufficient to contain adequate information for a reliable asymptotic approximation. The REML solution was close to values obtained from different sampling-based methods indicating that the present sample size was sufficient to estimate reliable genetic variation in different traits with varying heritability. The variance and heritability estimated by a nonparametric bootstrap estimate based on randomization of family effects gave comparable results as evaluated by REML for different traits. Hence, the nonparametric bootstrap estimate can be effectively used to understand whether the sample size is large enough to contain sufficient information under likelihood estimation assumptions.

Fish tyrosinase enzyme involved in melanin biosynthesis: Insights from physicochemical characterization, homology modeling, and virtual screening studies.

In the vertebrates, including fish, the tyrosinase enzyme plays an essential role in coloration. Modulation of tyrosinase activity is expected to alter the body pigmentation in fish and other vertebrate species. In the present study, physicochemical, functional, and structural properties of tyrosinase of three fish species viz., goldfish, Japanese medaka, and common carp were determined. The homology model was developed using the Chimera1.1.2, Swiss model, and Phyre2, and the best model was selected upon evaluation. Further, a virtual screening method was applied to identify the putative modulators using the PyRx- Virtual screening tool. The estimated physicochemical and functional properties of tyrosinase from the three species suggested that they all are hydrophobic, acidic, thermostable, with a high extinction coefficient (Cys, Trp, and Tyr) and have transmembrane-segment. Based on virtual screening against 13,000 compounds from the zinc database, five compounds were determined as potent modulators of fish tyrosinase with a binding energy of -7.0 to -8.8 Kcal/mol. Of these, Pilosine (ZINC13469966) was found to be the best putative modulator with low binding energy and properties of standardized drugs. This study showed that the tyrosinase function could be modulated to alter the pigment formation in fish species by using small compound.

A new species of Stolephorus (Clupeiformes: Engraulidae) from the Bay of Bengal, India.

A new fish species, Stolephorus tamilensis sp. nov., is described from the East coast of India. The major distinguishing characters are 5-6 small needle-like pre-pelvic scutes on belly; maxilla tip pointed, reaching to border of operculum, concave and indented in the preoperculum; 25-28 gill rakers on lower lobe of the first branchial arch; dorsal fin without spine; 17-19 anal-fin rays. Moreover, S. tamilensis sp. nov. present higher average genetic divergence values at mitochondrial cytochrome c oxidase subunit I and 16S rDNA loci in comparison with congeners. Also, nucleotide diagnostic characters exclusive to S. tamilensis are identified. Neighbor-joining analysis revealed close relation between S. tamilensis  and S. andhraensis.