Abstract
Pharmaceuticals are compounds manufactured for the improvement of the health of humans and animals. However, their persistence in the environment has caused indirect effects on aquatic biota. Antiretrovirals (ARVs) have been commonly found in the environment and studies have indicated effects on aquatic biota. South Africa has the largest antiretroviral therapy (ART) in the world, improving the quality of life and reducing mortality. These drugs, however, have had negative impacts on water quality and aquatic organisms. Tenofovir disoproxil fumarate (TDF) was introduced as an improved nucleoside reserve transcriptase inhibitor (NRTI), used to suppress the replication of HIV/AIDS. This drug was introduced because of its high efficacy, easy penetration and most importantly, the reduced side effects on humans.
Like other ARVs, TDF has been detected in surface water in South Africa and there is limited information available on how this ARV affects aquatic organisms. Human studies have indicated hepatic toxicity, nephrotoxicity and bone toxicity in humans. Studies conducted on other types of ARVs have indicated liver and kidney histopathology after exposure. Because there is limited information on how TDF impacts fish in their early life stages, this study aimed to investigate the effects of TDF on the hatching success, growth, survival, morphology, and histology of the early life stages of O. mossambicus.
To carry out the experiment, O. mossambicus were bred under controlled laboratory conditions at the University of Johannesburg Research Aquarium, and the embryos were exposed to environmentally relevant concentrations of TDF. After hatching, the larvae were further exposed for 30 and 60 days post-hatching (PH), and the exposures were divided into four groups namely; the control, solvent control, TDF Low (0.25 μg/L) and TDF High (2.5 μg/L). The fish were fed commercial tilapia food twice a day from when the yolk sac was depleted until the end of the experiment. The hatching success was recorded for each group, and specimens were sampled at day 1, 30 and 60 PH for histological assessment.
Length and mass measurements were recorded on sampling days and used to assess the condition factor and survival. Morphological evaluations were conducted and any morphological deformities were noted. Qualitative and semi-quantitative histological assessments were conducted to assess the liver and kidney histology of 30 and 60-day old fry. Exposures were repeated 3 times.
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Hatching success was not affected and was above 90% for all groups in all repeats. There was a delay in the hatching of eggs exposed to TDF, but the delay was not statistically significant (p = 0.058). Mortality was observed at the start of exogenic feeding, when the yolk sac was depleted, but survival rates were not affected. The condition factor was significantly affected at day 30 PH due to the variation in the length and mass of the fry. This was supported by the statistically significant differences (p = 0.006) observed between the solvent control and the exposed groups (0.25 μg/L and 2.5 μg/L TDF).
Morphological deformities were observed in less than 5% of fish, in all groups, including the control groups. The deformities included missing tails, curved spines, a missing eye and one case of an abnormal liver that developed in the gill chamber. Observed histological alterations included vacuolation and nuclear alterations in the liver and posterior kidney of fish in all groups. A semi-quantitative assessment indicated that the fry exposed to the higher concentration of TDF had more severe alterations than fish exposed to the lower concentration. Furthermore, 30-day old fry were more affected than the 60-day old fry, for both concentrations.
Liver histological assessments of 30-day old fry indicated significant differences between the solvent control and TDF Low (0.25 μg/L, p = 0.046), and between solvent control and TDF High (2.5 μg/L, p = 0.009). Liver histological assessments of 60-day old fry indicated significant differences between solvent control and TDF L groups (p = 0.045). Furthermore, kidney histological assessments of the 30-day old fry indicated significant differences between the solvent control and TDF L (0.25 μg/L) group (p = 0.036). However, histological assessments of the kidneys of 60-day old fry indicated no significant differences between the groups (p = 1.000).
Based on the results, TDF did not have any effects on the hatching success, growth, survival and morphology of the early life stages of O. mossambicus. However, TDF did exert more histological response in the livers and kidneys of exposed O. mossambicus early life stages i.e. higher organ index values.