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Cathepsin L (MrCathL) was identified from a constructed cDNA library of freshwater prawn Macrobrachium rosenbergii. MrCathL full-length cDNA is 1161 base pairs (bp) with an ORF of 1026bp which encodes a polypeptide of 342 amino acid (aa) long. The eukaryotic cysteine proteases, histidine and asparagine active site residues were identified in the aa sequence of MrCathL at 143-154, 286-296 and 304-323, respectively. The pair wise clustalW analysis of MrCathL showed the highest similarity (97%) with the homologous cathepsin L from Macrobrachium nipponense and the lowest similarity (70%) from human. Phylogenetic analysis revealed two distinct clusters of the invertebrates and vertebrates cathepsin L in the phylogenetic tree. MrCathL and cathepsin L from M. nipponense were clustered together, formed a sister group to cathepsin L of Penaeus monodon, and finally clustered to Lepeophtheirus salmonis. High level of (P<0.05) MrCathL gene expression was noticed in haemocyte and lowest in eyestalk. Furthermore, the MrCathL gene expression in M. rosenbergii was up-regulated in haemocyte by virus [M. rosenbergii nodovirus (MrNV) and white spot syndrome baculovirus (WSBV)] and bacteria (Vibrio harveyi and Aeromonas hydrophila). The recombinant MrCathL exhibited a wide range of activity in various pH between 3 and 10 and highest at pH 7.5. Cysteine proteinase (stefin A, stefin B and antipain) showed significant influence (100%) on recombinant MrCathL enzyme activity. The relative activity and residual activity of recombinant MrCathL against various metal ions or salts and detergent tested at different concentrations. These results indicated that the metal ions, salts and detergent had an influence on the proteinase activity of recombinant MrCathL. Conclusively, the results of this study imply that MrCathL has high pH stability and is fascinating object for further research on the function of cathepsin L in prawn innate immune system.

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In the present investigation, efforts have were made to investigate out the antibacterial activity of skin mucus and intestinal mucus of five different Channa sp viz; Channa striatus, C. micropeltes, C. marulius, C. punctatus and C. gachua. The mucus collected were tested against five pathogenic bacteria namely Aeromonas hydrophila, Pseudomonas aeruginosa, Escherichia coli, Vibrio fischeri and V. anguillarum using Muller Hinton agar plates by using disc diffusion method. All the five Channa sp showed a better antibacterial activity and among the five species C. striatus showed a broad spectrum of antibacterial activity of skin mucus against A. hydrophila (19.5 ± 2mm). P. aeruginosa (28 ± 2.9mm) and V. anguillarum (24.5 ± 2.4mm) and intestinal mucus against A. hydrophila (16 ± 1.4mm), P. aeruginosa (29 ± 3.2mm), V. anguillarum (18.3 ± 1.5mm) and V. fischeri (21.5 ± 1.8). Among the five pathogens tested the maximum antibacterial activity was observed for the skin mucus against V. fischeri and the intestinal mucus against P. aeruginosa..