Seasonal occurrence and variation of ectoparasites in Nile tilapia (Oreochromis niloticus) in the Federal District, Brazil

The present study assesses the diversity and seasonal variation of parasites in Oreochromis niloticus (Nile tilapia) cultivated in excavated tanks in the Federal District, Brazil. A total of 120 specimens of O. niloticus were collected in 12 monthly collections. Water quality parameters were checked at all tanks. The animals, sacrificed by immersion into anesthetic solution, had the gills scraped, in which the mucus was analyzed under an optical microscope. Parasitological examination showed Trichodina sp., Epistylis sp., Ichthyophthirius multifiliis, and Monogenea helminths in the fish gills. We found statistically significant differences between Monogenea parasites collected in the fall and winter and between I. multifiliis protozoans collected in fall-winter and winter-summer periods. Except for Epistylis sp., all parasites showed abundance peaks in O. niloticus specimens collected during the winter, which may characterize the seasonality of these parasites in the Federal District region. Monogenea helminths were the most prevalent among the parasites found, with the highest prevalence during the fall. The mean abundance of parasites was similar between the fall and winter. However, the abundance of monogenetic trematodes was higher between the winter and summer. I. multifiliis showed significant variation between fall-winter and winter-summer periods.(AU)

Quality of semen in the reproductive cycle of Cachara (Pseudoplatystoma fasciatum) raised in captivity

In this study, we evaluated the semen quality of Cachara (Pseudoplatystoma fasciatum) raised in captivity during its reproductive period. For the evaluation of qualitative parameters, we analyzed: sperm morphology, sperm motility, and sperm vigor;while for the quantitative parameter, we analyzed sperm concentration. In general, the main significant difference was found in March, with a motility rate of 40% and a duration of 39 seconds. The highest mean concentration (1.2x10⁸) was observed in February, as well as the highest percentage of defects in the intermediate part of the spermatozoa (59%). The morphological analysis of spermatozoa showed an average of 24.2% abnormalities in the head and 22.7% in the intermediate part of spermatozoa of P. fasciatumfor the four months studied. We did not find any evident relationship between the climate changes evaluated and the qualitative and quantitative parameters. The greatest difference between the percentage of normal spermatozoa and the sharp increase of defects in the intermediate piece, observed in February, can be explained by the sudden climate change, with a significant decrease in temperature and relative humidity, and increase in precipitation. These findings demonstrate the importance of maintaining an optimum climate interval during the breeding season for P.fasciatum.