Abstract
This study aimed to determine the lethal concentration 50% (LC$_{50}$) and behavioral, hematological, biochemical, histopathological, and genetic disorders of fipronil for Rhamdia quelen in acute toxicity tests for 96 h. To determine the LC$_{50}$, 42 juveniles were distributed in groups of 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.8 mg L$^{-1}$ of fipronil. For other evaluations 36 silver catfish were divided into control, 0.3 mg L$^{-1}$, and 0.4 mg L$^{-1}$ groups. Blood, kidneys, livers, and gills were collected for evaluation. The LC$_{50}$ calculated with probit-type regression was 0.811 mg L$^{-1}$ at 48 h of study. There was total mortality of 0.8 mg L$^{-1}$, reduction in hematocrit values, and increase in liver enzymes. Liver samples showed cytoplasmic vacuolization and cellular degeneration, among other changes. Gills presented vascular congestion, complete fusion of secondary lamellae, and epithelial cell hypertrophy. In the kidneys, changes such as Bowman?s capsule clearance, tubular degeneration, and glomerular capillary dilatation, among others, were common. Erythrocytes showed morphological alterations without increased micronucleus development. Fipronil induces a clinical condition of anemia, alterations in liver enzyme levels, nuclear erythrocyte changes, and liver, gill and kidney damage in the silver catfish.
Highlights
The aquatic environment is exposed to various chemicals produced by humans, such as xenobiotics
Pesticides such as deltamethrin (6), fipronil (10), bifenthrin pyrethroids (10,11), and cypermethrin (12) are related to behavioral changes and/or to the drop in swimming performance in larvae and juveniles of several species of fish exposed to acute intoxications
The toxicity of fipronil in fish varies according to species with lethal concentrations (LC50) ranging from 0.042 mg L–1 in Nile tilapia (Oreochromis niloticus) to 0.43 mg L–1 in common carp (Cyprinus carpio) (13)
Summary
The aquatic environment is exposed to various chemicals produced by humans, such as xenobiotics. The accumulation patterns of these substances are different for different organisms and depend on the balance between the rate of assimilation and rates of metabolization and elimination of chemical compounds (1). Biochemical characteristics are important physiological parameters of fish, changes of which indicate metabolic variations and cellular processes of the organism, evidencing the effects of pollutants and their mechanisms of degradation in the ecosystem (2,3). Hematological parameters are used as indicators of stress resulting from endogenous or exogenous changes in fish (4). Evaluation of blood parameters can be useful to monitor the physiological status and diagnose fish pathologies and intoxication (5,6). Toxicity levels can be noted in histological changes in fish, which are sensitive tools for detecting the toxic effects of chemical compounds on target organs considered to be indicators of exposure to environmental pollutants (7)
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