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.

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A 60-day feeding trial was conducted to optimally reduce the fishmeal level in climbing perch (Anabas testudineus) fingerling diet using a dietary brewer’s spent yeast biomass (BSY) based diet. In this study, five isonitrogenous (35% CP) and isocaloric (19.15 MJ/Kg) feeds were prepared by replacing 0 (BSY0), 25% (BSY25), 50% (BSY50), 75% (BSY75) and 100% (BSY100) of fishmeal protein using BSY protein. A total of 225 numbers of uniform-sized climbing perch fingerlings (3.29 ± 0.09 g) were randomly stocked in the 15 rectangular FRP (Fiber-reinforced plastic) tanks (150 L capacity). The experimental fish were fed twice daily at 4% BW for the first fortnight and later reduced to 3% BW based on satiation. At the end of the feeding trial, the weight gain (WG) of fish increased with the increasing BSY incorporation rates corresponding to fishmeal content and peaked at 77.88%, and beyond that, WG decreased. Food conversion ratios decreased as dietary BSY levels increased and peaked at 76.28%. All other growth and feed utilization parameters followed a similar trend of weight gain. Hepatosomatic index (HSI) and viscerosomatic index (VSI), A:G ratio, serum catalase activity, and monocytes were unaffected and the total serum protein, albumin, globulin, alanine aminotransferase (ALT), aspartate aminotransferase (AST), respiratory burst activity, lysozyme levels, myeloperoxidase activity, hemoglobulin, red blood cells, white blood cells, neutrophils, eosinophils, lymphocytes, and gut protease activities were increased significantly (P &lt; 0.05) with the increasing replacement levels and peaked between 25 and 75%. The serum SOD activity and total platelets were decreased, whereas the serum uric acid and gut amylase activities were increased significantly to the increasing levels of FM replacement in the diets (P &lt; 0.05). Among treatments, the BSY100 resulted in an overall poor growth response combined with relatively reduced values in nearly all biochemical parameters. The whole-body composition was nearly unaffected. The integrated biomarker response of various biochemical indicators from the different treatments has shown that the 50% fishmeal protein can be optimally replaced by BSY, which would cause an 18% reduction in the Economic conversion ratio (ECR) and −270.28 gCO2e– reduction in carbon footprint value per kg of climbing perch fingerlings production.

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Real‐time quantitative PCR (RT‐qPCR) is the most advanced and commonly used method for quantification of gene expression levels because of its high sensitivity, specificity and accuracy. The analytical capability of RT‐qPCR, on the other hand, is dependent on precise normalization by using the most stable reference genes. The present study was undertaken to find the best‐suited reference gene for normalization of qPCR data for ontogenetic studies of striped murrel. Four commonly used and constitutively expressed genes, namely beta‐actin (β‐actin), glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH), elongation factor 1‐alpha (EF1α) and 18 S ribosomal protein (18 S RNA) were screened and evaluated for their expression stability in developing larvae from 1 to 35 days post hatch (dph). The stability and suitability of these genes were determined by using four different algorithms; namely, delta Ct, BestKeeper, geNorm and NormFinder. The four algorithms together generated a comprehensive ranking EF1α being the most stable, followed by GAPDH and β‐actin as the least stable gene. This is the first report evaluating the most suitable reference gene for mRNA expression studies in C. striata, in the context of ontogenetic development.