Abstract
This study describes a long-term toxicity test within a period of 2 months using zebrafish (Brachydanio rerio) as the test species and concentrations of 0.05, 0.5, 5 and 50 μg/l DDT as a model substance. By collecting and counting the number of sperm released during separate mating events we observed that gametes are released asynchronously. Sperm is released in the form of sperm trails laid on the nest surface; subsequently active spermatozoa leave the trails and move in the water for several minutes. Sperm trails consists of bands of viscous material in which sperm is embedded. The water samples for the estimation of sperm presence were collected gradually within 180 min after 24 hr, 2 weeks, 1 month and 2 months of exposure. It was established that the reduction in count, activity of sperm and the average life span of sperm trails were significant (p < 0.05) at the tested concentrations 5 μg/l and 50 μg/l DDT after 1 month of exposure. In conclusion, this study demonstrates that long exposure time and higher DDT tested levels accelerate the occurrence of negative effect on the number and activity of sperm released as well as the life span of their trails.
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