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The present study was carried out to evaluate the effect of oxytetracycline (OTC)dosing at five different concentrations, viz., 0 mg (0X), 80 mg (1X), 240 mg (3X), 400 mg (5X) and 800 mg (10X) kg -1 biomass day -1 for 30 consecutive days on the growth, safety and intestinal histology of Nile tilapia, Oreochromis niloticus (L.) juveniles. The OTC-residues in the edible muscle were detected at scheduled intervals by LC-MS/MS. A dose-dependent decline in feed intake, biomass and survival were recorded in OTC-dosed fish. The OTC-residue levels were 0, 204.75±45.75, 318.00±0.00, 778.50±145.50 and 684.00±18.00 ng g -1 in 0X, 1X, 3X, 5X and 10X groups, respectively on day 30 OTC-dosing, which reduced subsequently. Relatively mild histopathological lesions including degeneration of epithelial layer, loss of absorptive vacuoles, necrotized intestinal villi, mucinous degeneration, and necrotized absorptive region were observed in the intestine of OTC-dosed fish. Lamina propria swelling was the characteristic change observed in the 10X group on day 15. The observed data revealed that OTC-dosing is reasonably safe at the therapeutic dose of 80 mg kg -1 biomass day -1 . However, the precise dose for safe usage of OTC is to be determined according to the culture conditions and species cultured.

Effect of oral OTC-therapy against Aeromonas caviae infection by two challenge routes in Nile tilapia are presented • The intramuscular challenge effected high mortalities than abrasion-immersion challenge • The results demonstrated the positive effect of oral OTC-therapy in overcoming the Aeromonas caviae challenge and improving wound healing. • The extent of damage in untreated Nile tilapia lasted longer in both challenge routes 2 Roy, A.; et al.

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To assess the effects of an antiparasitic aquadrug emamectin benzoate (EB) on the serum biomarkers of Nile tilapia, Oreochromis niloticus when -1 -1 fed at the recommended dietary dose regimen of 50 µg kg biomass day for 7 consecutive days (1X) and compare with the control and 10 times the recommended dose (10X).Nile tilapia were divided into three groups of thirty fish each. The fish of Group 1 were fed with control feed. Group 2 and 3 were fed with 50 -1 -1 µg and 500 µg EB kg biomass day , respectively, for 7 days followed by 45 days of post-dosing observations. Serum samples from different EB-dosed Nile tilapia were collected at scheduled interludes to analyse the serum biomarkers, viz., glucose, aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatinine and C-reactive protein (CRP) by standard kits.Seven days of EB-dosing reduced the biomass by 6.91%. The levels of fish serum biomarkers increased significantly on day 7 EB-dosing. Their levels consequently reduced, but did not reach normalcy, except ALT, AST and CRP, on day 45 post-EB-dosing at the recommended dose. The results demonstrated that the physiological state of apparently healthy Nile tilapia was persuaded by oral EB-dosing.The effects of EB-dosing on serum biomarkers of Nile tilapia are revocable. Nevertheless, the observed results on the biomass reduction and elevated levels of serum biomarkers, raises concern on the effectiveness of oral EB-dosing in Indian condition. Anti-parasitic drug, Emamectin benzoate, Oral-dosing, Oreochromis niloticus, Serum biomarkers Effects of oral-dosing of an antiparasitic drug emamectin benzoate on the growth and serum biomarkers of Oreochromis niloticus (L.) juveniles

Antibiotics are considered an important primary therapy for bacterial diseases in aquaculture. This study evaluated the in uence of oral administration of oxytetracycline (OTC) on feed intake, growth, mortality, residue accumulation and clearance, and histopathological changes in the vital organs of six groups of Nile tilapia Oreochromis niloticus when fed at 0-10 times the therapeutic dose (1X: 80 mg/kg biomass/day) for 10 and 20 consecutive days. The feed intake was reduced only slightly, viz., 2% in 10 days and 4.25% in 20 days dosing trials at 1X-dose compared to control. While in other groups, an OTCdose-dependent reduction in feed intake up to 31.25% was noted. The sh of 0.5X and 1X groups recorded signi cantly high biomass; while the other OTC-dosed groups recorded signi cantly lower biomass than the control. The fold change in biomass between the control and 1X groups was insigni cant. A dosedependent mortalities were recorded in OTC-dosed sh in 10 days (1.67±2.89-6.67±2.89%) and 20 days (3.33±2.89-8.33±2.89%) trials. The OTC concentration in sh muscle established a dose-and timeresponse relationship. The OTC residue levels in muscle even on day 20 OTC-dosing were lower than the maximum residue limit permitted by Codex Alimentarius (200 ng/g). On day 23 post-OTC-dosing, the residue levels were traces to <10 µg/g in all groups, except the 10X group. The OTC-dosing caused mild to moderate pathological changes in the gills, liver and kidney of O. niloticus and the sh were able to mount adaptive biological responses to overcome the stress with time.