Influence of dietary emamectin benzoate on the biological responses of monosex (all-male) Oreochromis niloticus (L.) fries.

The application of antiparasitic drugs plays a crucial role in the removal of infectious parasites in aquaculture. Emamectin benzoate (EB) is predominantly used as a feed premix against ectoparasites on temperate fish. This study evaluated the influence of 14 days of EB-dosing at 0-10 times the recommended dose (1X: 50 µg/kg biomass/day) on the biological responses and accrual/depletion of EB-residues in a tropical fish monosex Oreochromis niloticus fries. A significant dose-dependent reduction in feed intake by 3.50% in 1X and 43.00% in 10X groups, and an increase in mortalities from 2.92% (1X) to 11.25% (10X) during the EB-dosing period was noted. A significant increase in glucose and alkaline phosphatase and reduction in calcium and chloride ions, superoxide dismutase (SOD) and acetylcholinesterase levels in the muscle and/or brain tissue was observed. On day 21 post-EB-dosing, the levels of muscle glucose and SOD reached normalcy in the 1X group, while the levels of other biomarkers failed to recuperate. The EB-residue levels peaked on day 14 EB-dosing (2.77 ng/g) in the 1X group and decreased later with detectable levels (0.03 ng/g) even on day 21 post-EB-dosing. The EB-residue levels were within the permissible limits of the Canadian Food Inspection Agency and the European Commission. The EB-dosing negatively influenced the health of O. niloticus by altering the physiological state in a dose- and time-dependent way. The results suggested that the use of EB might be plausibly risky in tropical aquaculture.

Accumulation and clearance of tissue residues and health status of Nile tilapia Oreochromis niloticus (L.) juveniles as influenced by the extended oral oxytetracycline-dosing.

Antibiotics are considered an important primary therapy for bacterial diseases in aquaculture. This study evaluated the influence 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 (1×: 80 mg/kg biomass/day) for 10 and 20 consecutive days. The feed intake was reduced only slightly, viz., 2% in 10-day and 4.25% in 20-day dosing trials at 1× dose compared to control. While in other groups, an OTC-dose-dependent reduction in feed intake up to 31.25% was noted. The fish of the 0.5× and 1× groups recorded significantly high biomass, while the other OTC-dosed groups recorded significantly lower biomass than the control. The fold change in biomass between the control and 1× groups was insignificant. Dose-dependent mortalities were recorded in OTC-dosed fish in 10-day (1.67-6.67%) and 20-day (3.33-8.33%) trials. The OTC concentration in fish muscle established a dose- and time-response relationship. The OTC residue levels in muscle even on day 20 OTC-dosing were lower than the maximum residue limit (MRL) 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 10× group. The OTC-dosing caused mild to moderate pathological changes in the gills, liver and kidney of O. niloticus and the fish were able to mount adaptive biological responses to overcome the stress with time.

Dietary therapeutic dose of oxytetracycline negatively influences the antioxidant capacity and immune-related genes expression in Nile tilapia Oreochromis niloticus (L.).

Effects of the dietary therapeutic dose of oxytetracycline (OTC) at 80 mg/kg biomass/day for consecutive 10 days on the behaviour, feed intake, mortality, residue accumulation and depletion, antioxidant capacity and immune-related genes expression in juvenile Nile tilapia Oreochromis niloticus were evaluated. OTC-dosing caused mortalities, reduced feed intake, and biomass reduction at 24.5-28.5 °C. OTC residues recorded on day 10 (161.40 ± 11.10 ng/g) were within the maximum residue limits of the Codex Alimentarius. The withdrawal period was 7 days as per the European Commission's regulation. Traces of residues were present even on day 42 post-OTC-dosing. Dietary OTC reduced the antioxidant capacity of the liver and muscle tissues and down-regulated the expression of tumour necrosis factor-α, interleukin-1ß, and heat shock protein-70 genes in the liver significantly during the dosing period. The data generated on the biosafety of OTC-dosing may offer inputs for the development of management strategies in maintaining fish health and food safety.