Prevalence of parasites on nile tilapia (oreochromis niloticus) fry during sex reversal stage at Mig Fish Farm, Mayuge District- Eastern Uganda

Abstract

This study investigated the occurrence, infestation levels and diversity of ecto-parasites during sex reversal in Nile tilapia fry. Two subpopulations were used to study the prevalence of parasites in fry that is one fed on sex reversal hormone and another that was not treated with the hormone. Fish fry were collected from the brood stock ponds using a seine net (Weinstein and Davis, 1980) counted and their weight measured using a digital weighing scale. A total of 150 fish fry were examined for ectoparasites using standard parasitological procedures. Five species of parasites were identified, consisting of 3 protozoans (Trichodina heterodentata, Trichodina magna, and Trichodina constrostrigata) and 2 monogeneans (Gyrodactylus salaris, and Dactylogyrus vastator). The study findings showed that Trichodina heterodentata was the most abundant followed by Gyrodactylus salaris, Trichodina magna, Dactylogyrus vastator and Trichodina constrostrigata being the least abundant. Furthermore, the prevalence of the parasites in examined fish fry was significantly higher in the sample treated with sex reversal hormone (91.33%) than in the fish fry sample not treated with the hormone (62.67%). Nevertheless, the diversity of parasites was low illustrated by the low value of Shannon Weiner diversity indices recorded in sex reversed sample (H=1.07) and control group (H=0.74). In the view of the study findings and the pathological effects of the different parasites identified on the examined fry samples, MIG fish farm is liable to facing high mortalities, increased cost of production, reduced profit margin, losses and at the extreme failure of the business enterprise. Therefore, appropriate and strategic management measures should be designed and followed for proper management and business flow.