Kua, B.C. National Fish Health Research Centre Azila, A. National Fish Health Research Centre Siti Zahrah, A. National Fish Health Research Centre Roziawati, M.R. Pulau Layang-Layang Project Office Malaysia Md. Akhir, A. Pulau Layang-Layang Project Office Malaysia Faazaz, A.L. Fisheries Research Institute Lu, K.C. Tanjung Badak Breeding Centre Malaysia A fish health diagnosis activities were carried out at the hatchery in Tanjung Badak Breeding Centre, Tuaran, Sabah and in the floating cages in Pulau Bhai, Sandakan, Sabah in 2006 and 2007. A total of 116 fish samples comprise of tiger grouper (Epinephelus fuscogutatus), red snapper (Lutjanus erythropterus), sea bass (Lates calcarifer), Papuan black snapper (Lutjanus goldiei) and Napoleon wrasse (Cheilinus undulatus) were sampled. The fish samples were tested for viruses, parasites and bacteria. A total of 228 samps from 'pooled' organs of kidney, spleen, brain, liver and eye were tested for Iridovirus (RSIVD) and Nodavirus (VNN) using IQ2000Tm Qiagen PCR kit. The results indicated that 17.2% of tiger grouper from Tanjung Badak dan Sandakan were positive with RSIVD whereas 7.78% of sea bass and 2.6% of red snapper were positive with VNN. Parasites such as monogeneans (Diplectanid pseudorhabdosynochus), capsalid (Benedenia sp.), protozoa Brooklynella sp. and leeches were found in tiger grouper and monogeneans (Haliostrema sp.) in red snapper. Monogeneans were the most common parasite found in fish at high prevalence between 36.4-100% and mean intensity of 8.8-27, followed by Trichodina sp. at prevalence of 4.5-100%. Capsalid (Benedenia sp.) at prevalence of 20% caused significant mortalities and health problems to fish culture at floating cages. V vulnificus and V alginolyticus were isolated from skin abrasions, skin ulcer, liver and kidney. Bacteria such as Staphylococcus sp., and Micrococcus sp. were also found on the skin and internal organs of the fish with chronic skin ulcers.