Prevalence and seasonal variation of ectoparasites in cultured Nile tilapia Oreochromis niloticus in Saudi Arabia.

The prevalence, mean intensity and abundance of ectoparasites (monogeneans and trichodinids) from Nile tilapia Oreochromis niloticus were investigated during different seasons of two consecutive years, from January 2011 to December 2012. A total of 360 O. niloticus was collected from three fish farms located in the central region of Saudi Arabia. Prevalence, mean intensity and mean abundance of monogeneans on fish gills were found to be significantly (p < 0.01) higher in farm(C) (81.67, 495.23, 405.84 %) than farm (A) (7.5, 81.25, 8.34 %) and farm (B) (4.17, 62.5, 5 %) respectively. Similarly, the same parameters for trichodinids on gills were found to be significantly (p < 0.01) higher in farm (C) (97.5, 97.5, 97.5 %), followed by farm (A) (39.17, 234.37, 35.00 %) and farm (B) (6.67, 347.92, 30.00 %) respectively. The results of monogenean parameter on fish skin were found to be significantly (p < 0.01) higher in farm (C) (66.67, 443.68, 294.16) followed by farm (A) (16.67, 124.58, 21.67 %) then farm (B) (0.83, 25, 0.83 %) respectively. Similar results for trichodinid parameters on the skin were found to be higher (p < 0.01) in farm (C) (97.5, 875, 857.5 %), then farm (A) (26.67, 399.70, 215.01 %) and farm (B) (4.17, 154.17, 12.5 %) respectively. These results indicated that water quality and nutritional qualities were the major factors that affecting parasite occurrence, while the effect of temperature, seasonality and stocking density might have a secondary role on ectoparasite occurrence. Further studies should investigate that how the nutritional and water qualities affect the immunity of the fish to resist parasite infection.