A 330-day field trial was conducted to evaluate the effect of stocking density and feeding ration on stunted Labeo rohita (Hamilton, 1822) fingerling reared in floating net cages. The stunted fingerling of L. rohita with an average body weight 38.23 ± 1.90 g were stocked in cages (3 × 3 × 3 m) at different densities viz. T1 (10), T2 (15), T3 (20) and T4 (25) fish/m3 and fed with varying levels of feeding rations at 3, 4, 5 and 6% at each stocking density. The 4×4 factorial design was used, and each density and feeding level kept in triplicate, and fed with commercial pellet feed (crude protein 28% and fat 5%) twice in a day. The significant recovery was observed in the T1 (10*5 and 10*6) treatment groups, which showed highest Hb, RBC, PCV and lowest WBC content at the end of experiment. Similarly, significant changes were observed in glucose, cortisol and lactate dehydrogenase (LDH), which were highest in higher stocking density (T4), and normalized in lower stocking T1 (10*5 and 10*6) treatment groups. Histological examination showed, almost complete recovery of structural changes such as swelling/ edema primary lamellae, hyperplasia of basal epithelium between the secondary lamellae of gill and necrosis in liver of lower stocking densities (10 and 15 fish/m3). In contrast, greater structural changes in both the organs were observed in the higher stocking density groups (20 and fish nos/m3). Based on the results, it can be concluded that maximum growth and complete recovery (in term of haematology, stress and histological changes) were observed in lower stocking density (10 fish/m3) fed with 5 to 6% feeding levels. Hence, in an Indian reservoir cage-based cultures, 10 fish/m3 fed with 5 to 6% feeding rations can be recommended at commercial scale to get maximum and sustainable profit by using the stunted L. rohita fingerling.
The current study was conducted to evaluate the antibacterial activity of super-paramagnetic iron oxide nanoparticles (SPIONs) against Edwardsiella tarda from water. The antibacterial activity of different concentrations of SPIONs viz. 0, 6.25, 12.5, 25, 50, 100, 200, 500 and 1000 µM were assessed in sterilized distilled water with different initial bacterial loads of E. tarda viz. 1×103, 1×104, 1×105, 1×106 and 1×107 CFU ml− 1 at various exposure time (15, 30, 45 and 60 min). At lowest bacterial load 1×103 CFU ml− 1, > 98% bacteria was removed by 500 µM of SPIONs concentration group after 15 min exposure, which was increased up to 100% by increasing exposure time 45 min. However, at highest bacterial load 1×107 CFU ml− 1, > 78% bacterial load was removed by highest SPIONs concentration (1000 µM) by 15 min exposure, which was further increased > 85.32% by increasing the exposure time 60 min. The antibacterial activity was increased with increasing the concentration of SPIONs as well as exposure time while increasing the bacterial load the activity was decreases. At an initial bacterial load of E. tarda (1×103 to 1×107 CFU ml− 1), the effective concentration (EC50) ranged between 61.36 to 372.80 µM respectively after 15 to 60 min exposure. Thus, it can be concluded that the antibacterial activity of SPIONs depends on concentration and exposure time. To remove high bacterial load require high amount of SPIONs and exposure time as well. Hence, SPIONs can be used as a biocidal agent to treat Edwardsiellosis in fish.
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