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Tail and fin rot disease (TFRD) is a big issue in the production of spotted snakehead, Channa punctata Bloch. The aims of the present study were to isolate and identify the bacterial pathogen causing TFRD, to detect histopathological changes in tissues (fin, tail, liver, and kidney), and to ascertain the antibiotic sensitivity pattern of the isolate. Out of six bacterial isolates, only the isolate DJ1990 was found to be the causal candidate of TFRD in C. punctata. Identical histopathological changes were detected in tail, fin, liver, and kidney under light and scanning electron microscope in both collected diseased fish and artificially infected fish. The isolate was identified as Pseudomonas aeruginosa strain DJ1990 (National Center for Biotechnology Information Ace. No. KX709967) based on the biochemical characterization tests and 16S rDNA sequence‐based phylogeny analysis. Artificial challenge test demonstrated that the strain DJ1990 was highly virulent (100% mortality at 48 h of postinjection period at the concentration of 1.5 × 107 CFU/g of body weight) for C. punctata. The isolate exhibited sensitivity to the broad‐spectrum antibiotics but was resistant against aztreonum. To the best of our knowledge, this is the first report of P. aeruginosa as a TFRD‐causing candidate in C. punctata.

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Length-weight relationships (LWRs) are presented for two fish species: Schistura fasciata Vishwanath, 2011 and Schistura reticulofasciata (Singh and Bănărescu, 1982), sampled from the Simsang River in Meghalaya, India. Fishes were caught seasonally from January to December 2015, with cast nets (10-15 mm mesh size) and electrofishing devices. The b values in the LWRs were determined as 3.09 for S. fasciata and 3.318 for S. reticulofasciata. | 1037TALUKDAR eT AL. a digital slide calliper (Mitutoyo, CD-8″CSX) to the nearest 0.01 mm and the values converted into centimetres. Body weight was taken with an electronic balance (TP 303, Denver Instrument, Germany) to the nearest 0.01 g. The relationships between total length and weight were determined through linear-regression equation of log TW = log a + b log TL. Log-log plots within species were done to remove outliers using SPSS 17.0 (SPSS Inc. Ltd., Sacramento, California). The 95% confidence limits for b (CL 95%) were calculated to determine if the hypothetical value fell between these limits (Froese, 2006). | RESULTSDescriptive statistics and estimated LWR parameters for the two fish species from Simsang River are shown in Table 1. A total of 200 specimens (S. fasciata = 69, S. reticulofasciata = 131) were used to estimate the LWRs. | DISCUSSIONNo LWR data are available for either of the two species in FishBase (Froese & Pauly, 2016). The 'b' values for S. fasciata and S. reticulofasciata (calculated as 3.09 and 3.318, respectively) were within the expected range of 2.5-3.5 (Froese, 2006). Comparing the results for the two species against the Bayesian approach, parameter 'a' was found to be within the expected range for elongated fish species (i.e. 0.0018-0.00842 95% range of a) (Froese, Thorson, & Reyes, 2013).

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