High prevalence and mean intensity of trichodinids and monogeneans on Nile tilapia (Oreochromis niloticus) in Indonesian hatcheries.

Abstract

This study describes recent infestations of ectoparasites on tilapia fingerlings in several hatcheries. High mortality of fingerlings and juvenile fish often occurs in hatcheries but the causative agents remain unclear. Nile tilapia fingerlings were obtained from three hatcheries in South Sulawesi, Indonesia. The fish were euthanized in clove oil, length and weight were measured, and the whole body and gills were examined for ectoparasites. Trichodinids were silver stained with 2% AgNO3, whereas monogeneans were placed in glycerin-alcohol and examined under a microscope. Other protozoans were placed directly on fresh mounts and identified under a compound microscope. The monogenean parasites were cleaned and placed in a microtube containing 70% alcohol for molecular identification. Trichodinid (Trichodina centrostrigeata, T. magna, Paratrichodina africana, Trichodinella sp., and Tripartiella sp.), and monogenean (Gyrodactylus sp. and Cichlidogyrus spp.) parasites were found in highly prevalent. The Cichlidogyrus specimens were morphologically identified as C. sclerosus, C. halli, and C. thurston, but only C. sclerosus and C. halli were confirmed based on partial 28S rRNA. The Gyrodactylus specimens were morphologically identified as G. cichlidarum and confirmed based on the ITS region. This is the first time that T. centrostrigeata and P. africana have been confirmed on fish from hatcheries and is also the first time that C. sclerosus, C. halli, and G. cichlidarum have been verified in Indonesian hatcheries based on a molecular technique. The high infestation rates of these parasites were likely caused by rearing the fish under stressful conditions, indicating low biosecurity and poor health management practices in the aquaculture facilities.