RESUMO
Fish parasites can be used as bio-indicators to evaluate pollution degree in aquatic ecosystems. Limited research has, however, investigated the potentiality of these parasitic worms to tolerate various environmental factors. This study, therefore, investigated whether the gill, Quadriacanthus monogenean parasites of Bagrus bajad Forskål, 1775 are potential bio-indicators of aquatic ecosystem health. The seasonal differences in prevalence, mean intensity and abundance of Quadriacanthus species of Clarias gariepinus varied between each other and between the three localities. Most Quadriacanthus species exhibited their highest prevalence, mean intensity and abundance in Spring and/or Summer and their lowest values in Autumn and/or Winter. The seasonal differences in prevalence were significant for Q. kearni and Q. clariadis while a significant difference in the mean intensity between different seasons was recorded only for Q. aegypticus. Also, seasonal differences in the abundance were highly significant for Q. aegypticus and significant for Q. kearni. The total dissolved solids, Chlorides, Sulphate, Sodium, Cadmium and Lead were higher at Manzala Lake than standard permissible limits. The pH has significant correlations with the infestation levels of all Quadriacanthus spp. Dissolved oxygen showed a highly significant positive correlation with the mean intensity of Q. clariadis and a significant positive correlation with the abundance of Q. clariadis. Iron was the only heavy metal to record a significant positive relationship with the mean intensity of Q. kearni. It is noteworthy that Quadriacanthus species were found to have a noticeable ability to resist the effect of hazardous concentrations of many physicochemical and heavy metals parameters. Therefore, it is highly recommended that these monogeneans could be regarded as bio-indicators for water quality.
