The present study was conducted to assess the effect of oxytetracycline hydrochloride (OTC) in rohu, Labeo rohita, with graded doses viz., 80 (1×), 240 (3×), 400 (5×) and 800 (10×) mg kg −1 fish biomass day −1 respectively through feed. Four hundred and fifty healthy rohu juveniles (20 ± 0.12 g) were fed for 30 days followed by 10 days of withdrawal period. Each 10 days intervals, five fish were randomly sampled for blood, serum and tissue for estimation of growth, non-specific immune parameters, enzymatic activities and retention of OTC in muscle tissue. The results showed that there was no significant difference (p > .05) on growth in the treated fish compared with the control. Respiratory burst activity, myeloperoxidase activity, bacterial haemagglutination and haemolysis activities were enhanced significantly (p < .05) on 10 th and 20 th day in the fish fed with 80 and 240 mg kg −1 biomass day −1 respectively during the feeding trial compared with the control. Lactate dehydrogenase and alkaline phosphatase activity increased significantly (p < .05) in the fish fed with 400 and 800 mg kg −1 biomass day −1 respectively compared with the control. Liquid chromatographymass spectrometry/mass spectrometry study of muscle tissue reveals that OTC was retained in muscle tissue in a dose dependent manner and significantly (p < .05) lowest level (0.44 ± 0.03 ppb) was observed on 40 th day in the treated fish fed with 80 mg kg −1 biomass day −1 . Hence, 80 mg kg −1 fish biomass day −1 of OTC may be adhered in L. rohita for treating the fish through feed with 10 days of withdrawal period.

This study was conducted to evaluate the effect of dietary emamectin benzoate (EB) levels on immune responses, serum enzyme activities, and retention of EB in muscle tissue to establish the withdrawal period in rohu, Labeo rohita juveniles (avg. wt. 18 ± 0.11  g). To ascertain this, 450 healthy L. rohita juveniles were fed with EB in graded doses viz., at 50 (1x), 125 (2.5x), 250 (5x), and 375 (7.5x) μg kg-1 of fish biomass day-1, respectively, in triplicate for 21 days through a basal feed. Upon completion of 21 days, the same experimental fish were fed with basal feed (without EB) for another 14 days to measure the retention of EB in the muscle tissue. Each 7-day interval, five fish were randomly sampled. The results showed that respiratory burst activity, myeloperoxidase activity, bacterial haemagglutination, and haemolysis activities were improved significantly ( p < 0.05 ) in 1x and 2.5x dose fed group from 7th day onwards until 14th day. Few selected enzyme activities viz., LDH and ALP were found to be significantly ( p < 0.05 ) high in the fish fed with EB at 5x and 7.5x dose compared to 1x. The LC-MS/MS study of the experimental fish discloses that EB was retained in muscle tissue at a dose-dependent manner and significantly ( p < 0.05 ) lowest level ( 0.341 ± 0.03  ppb) was retained in the fish fed with 1x dose of EB. Hence, 1x dose of EB may be adhered to treat L. rohita juveniles through feed with 14 days of withdrawal period.

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High‐density fingerling rearing of pengba was conducted for 90 days in biofloc system (BFS) to study the effect of stocking density on growth, feed utilization, water quality, water use efficiency and health of animals. The study was conducted in 12 continuously aerated tanks (50 m3), grouped into four treatments T‐1, T‐2, T‐3 and T‐4, which were stocked with pengba fry (1.25 ± 0.05 g, 4.74 ± 0.70 cm) at 50, 60, 70 and 80 m−3, respectively. Supplementary feed (1 mm floating pellet) was fed twice daily, each time for 30 min duration. Molasses and urea were supplemented to maintain suitable C:N ratio at 15:1. No water exchange was given, except monthly compensation of evaporation loss. While water quality and most of the growth attributes in T‐1 and T‐2 remained similar, T‐3 at 70 m−3 density showed better water quality, higher survival and growth than T‐4. Body composition remained consistent across treatments despite impaired feed digestion and utilization associated with higher densities. The non‐specific immune responses in fingerlings increased from T‐1 to T‐3, but further density rise showed compromised immune in T‐4. Such results suggested 70 m−3 to be an ideal density for production of healthier fingerlings. But T‐4 produced 13.5% more fingerlings than T‐3, and fingerlings (7.56 ± 0.50 cm; 5.43 ± 0.09 g) were within acceptable size range for grow‐out stocking. T‐4 also showed the lowest total water use and the highest water implicating 80 fry m−3 to have more applicability. Thus, the study recommends 70–80 m−3 as ideal range for fingerling rearing of pengba in BFS.

Background: Caspase-8, a member of the family of conserved cysteine proteases, plays a crucial role in the initiation phase of the apoptotic death-signaling cascade and thereby attracts interest for its study across the animal species including fish. In India, rohu (Labeo rohita) is an important freshwater fish species; thus, this study on caspase-8 was undertaken to investigate its role during pathogenic invasion. Results: The complete cDNA sequence of Labeo rohita caspase-8 (Lrcasp8) consisted of 1746 bp nucleotides (nt) having an ORF of 1440 nt encoding a polypeptide of 480 amino acid (aa) residues with the molecular mass of ∼ 54.8 kDa. Structurally, Lrcasp8 comprised two DED domains (DED1 1-77aa and DED2 97-174aa ) and one CASc domain 230-476aa . Within the CASc domain, various putative motifs, viz., a large subunit (p20 237-360aa ), a small subunit (p10 389-474aa ), and a penta-peptide (QACQG 354-358aa ) active site, were identified. The secondary structure of Lrcasp8 protein comprised seventeen α-helices, eleven β-strands, and twenty-nine coils. Phylogenetically, it is closely related to common carp caspase-8 and exhibits significant (p < 0.05) similarity (88.3%) and identity (78.7 %) in their amino acid sequence. The tissue-specific expression of Lrcasp8 has been analyzed by quantitative real-time PCR assay, and it revealed the highest expression (~23-fold) in the blood and lowest in the spleen. In Aeromonas hydrophila and Edwardsiella tarda infection and rhabdovirus vaccination, caspase-8 gene expression in rohu fingerlings was significantly (p <0.05) induced in various organs/tissues. Infection of the Labeo rohita gill cells with A. hydrophila resulted in apoptosis and cell death with the induction of caspase-8 gene expression. Conclusion: This is the first report on the identification and structural characterization of caspase-8 cDNA and predicted protein and the analysis of caspase-8 gene expression in Labeo rohita following Aeromonas hydrophila and Edwardsiella tarda infections and rhabdovirus vaccinations. The data in this article together suggest the critical role of caspase-8 during infection and apoptosis in Labeo rohita.