Close to industrial activity and a major seaport in the Gulf of Thailand, Sichang Island has frequently suffered from pollution and oil spills. However, the environmental health status of the surrounding waters is relatively unknown. Between December 2017 and January 2018, we reared ninety Asian seabass (Lates calcarifer) in cage nets off the island and sampled blood to investigate nuclear abnormalities in erythrocytes and build leucocyte profiles. The fish were purchased locally and reared in locations where oil spills have been recorded. Environmental parameters were within the range of standard values. Erythrocyte nuclei had segmented, reniform and notched abnormalities; however, they dramatically varied after exposure. At the end of the three-month field experiment, very few micronuclei had been observed. Observed leucocytes were neutrophils, lymphocytes, and monocytes. The percentage of lymphocytes increased considerably, reaching a post-exposure peak at three months. Our data suggest that erythrocytic nuclear abnormalities of Asian seabass could be used as an early warning of toxic pollutants in the marine environment, and as a baseline environmental health indicator for Sichang Island and the surrounding area.

Koh Sichang area in Thailand is a sink for a wide variety of contaminants such as heavily polluted water from industry and oil spills. This situation may affect the health status of fish living in the area, but such information remains scarce. In this study, we evaluated the health status of java rabbitfish Siganus javus, an important marine fish in Koh Sichang, using hematological and histopathological biomarkers. All fish samples were collected from the Koh Sichang area during December 2017 and January 2018. Although the salinity, pH, and dissolved oxygen levels at sampling points were all within the normal range, abnormal nuclei were observed in erythrocytes (up to ~6% of all erythrocytes) and in some leucocytes (neutrophil, lymphocyte and monocyte). Visceral organs (gill, kidney and liver) were apparently normal in terms of gross morphology, but a wide variety of the histopathological alterations were found at the microscopic level: epithelial hyperplasia and aneurysm in gills; blood congestion and melanomacrophage centers (MMCs) in the liver; renal degeneration, granuloma and MMCs together with unidentified parasites in kidney. Calculation of semi-quantitative parameters [histological alteration index (HAI) and the average value of alteration (AVA)] demonstrated the highest frequency of histopathological alterations in kidney, suggesting that kidney is a sensitive organ. Overall, our observations suggest that S. javus in Koh Sichang is under the pathological state and warrants conservation efforts. Keywords: Erythrocytes, Fish Health, Hematology, Histopathology, Kidney