Acute toxicity, risk assessment, and exposure of Nile tilapia larvae after stress to sub-lethal concentrations of oxytetracycline

Document Type : Original research

Authors

Embrapa Meio Ambiente, Jaguariúna - SP, Brazil

Abstract

The present study evaluated the median lethal concentration (LC50-96h), risk assessment, biometrics of weight and length, and mortality of Nile tilapia Oreochromis niloticus larvae exposed to oxytetracycline (OTC). A total of 126 fish (mean weight: 32.25±3.74 mg; mean length: 13.01±0.64 mm; 7 larvae per aquarium) were utilized for the LC50-96h assessment. These fish were randomly distributed across 21 aquaria (1 L each) containing graded concentrations of OTC: 0.0, 2.01, 2.44, 3.31, 3.65, and 4.59 mg/L. Additionally, an acute stress test involving 180 fish (mean weight: 33.9±0.73 mg; mean length: 13.06±0.72 mm; 10 larvae per aquarium) was conducted, wherein the fish were subjected to air stress for 5 minutes before being randomly allocated to 18 aquaria (1 L each) and exposed to sub-lethal concentrations of OTC: 0.0, 0.03, 0.82, 1.65, 2.47, and 3.30 mg/L. Water quality parameters (temperature, pH, dissolved oxygen, conductivity, total ammonia, and total hardness) were monitored daily throughout the experiment. The LC50-96h for OTC in Nile tilapia larvae was estimated at 3.45 mg/L. Larval weight and length significantly decreased in both tests with increasing OTC exposure. Dissolved oxygen levels exhibited significant changes over 96 hours. The post-stress test revealed significant differences (P <0.05) in pH, temperature, and dissolved oxygen. Notably, pre-exposure to air stress exacerbated the toxic effects of sub-lethal OTC levels. Risk quotient analysis indicated a high potential risk for Nile tilapia larvae exposed to therapeutic OTC concentrations.

Keywords

International Aquatic Research
Volume 16, Issue 4
December 2024
Pages 343-354

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