Safety, tolerability and biological responses of Oreochromis niloticus juveniles upon oral oxolinic acid administration.

In aquaculture, oxolinic acid (OA) is used as a second-line treatment at 12 mg/kg biomass/day for seven consecutive days. The present study evaluated the biosafety of 21 days of dietary administration of OA at 0, 12, 36, 60 and 120 mg by assessing the growth, biochemical, erythrocytic morphological and histopathological alterations and residue levels in Oreochromis niloticus. A significant dose-dependent reduction in feed intake and biomass and an increase in mortalities and erythrocytic cellular and nuclear changes were recorded. Significant elevations in plasma glucose, creatinine, alkaline phosphatase, alanine transaminase and aspartate transaminase and a decline in calcium and chloride levels were documented. The kidney, liver and intestine histoarchitecture showed mild to marked alterations. The edible tissue OA residues peaked on day 21 and decreased upon cessation of administration in all the dosing groups. The residue levels in the muscle of the recommended dose group were well within the maximum residue limit set by the European Medicines Evaluation Agency. Although the current study hinted at the safety and tolerability of OA even during long-term usage in O. niloticus in Indian conditions, care must be exercised for its aquacultural application because of its listing as a critically important medicine for humans.

Pharmacokinetics and residues of florfenicol in Nile tilapia (Oreochromis niloticus) post-oral gavage.

In the study on Oreochromis niloticus, singular oral gavage of florfenicol (FFC) at 15 mg/kg biomass/day was conducted, mimicking approved aquaculture dosing. Samples of plasma, bile, muscle, intestine, skin, liver, kidney, gill, and brain tissues were collected at 0, 2, 3, 4, 6, 8, 12, 16, 24, 32, 48, 64, 96, and 128 hours (h) after oral gavage. LC-MS/MS analysis revealed FFC concentrations peaked at 12.15 µg/mL in plasma and 77.92 µg/mL in bile, both at 24 hours. Elimination half-lives were 28.17 h (plasma) and 26.88 h (bile). The residues of FFC ranked muscle>intestine>skin>liver>kidney>gill. In contrast, the residues of florfenicol amine (FFA) ranked kidney>skin>liver>muscle>gill>intestine>brain, particularly notable in tropical summer conditions. The minimum inhibitory concentration of FFC was elucidated against several bacterial pathogens revealing its superior efficacy. Results highlight bile's crucial role in FFC elimination. Further investigation, especially during winter when fish susceptibility to infections rises, is warranted.

Impacts of Oral Florfenicol Medication and Residues on the Kidney and Liver of Nile Tilapia Oreochromis niloticus (L.)

Florfenicol (FFC), an approved aquaculture antibiotic, is administered in feed at doses of 10-15 mg kg biomass-1 day-1 for 10 successive days. In this study, healthy Oreochromis niloticus were fed with 0-10 times the therapeutic dose of 15 mg kg biomass-1 day-1 for 10 days and tracked for 43 days post dosing. Assessments of residue accrual and depletion, oxidative stress, serum biochemistry, histopathology and extent of kidney and liver damages were made. FFC dosing reduced the feed intake significantly. The therapeutic dose produced no mortalities on day 10. Dose-dependent alterations in serum biochemistry were noted upon dosing. Several histopathological alterations were observed in the kidney and liver, which vindicated the toxic potentials of FFC. The residual FFC and florfenicol amine (FFA) accrual, depletion and oxidative stress responses, such as increased malondialdehyde, total nitric oxide, ferric reducing antioxidant power and reduced glutathione S-transferase activity, were documented. The dietary FFC persuaded the physiological state of O. niloticus, the effects of which normalized sparsely with time upon cessation of dosing at the higher doses. The study provided a brief outlook on the physiological responses upon oral FFC administration, which should be kept in mind during its application for fish health safety purposes.

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.