Prevalence and infestation intensity of a piscicolid leech, Zeylanicobdella arugamensis on cultured hybrid grouper in Brunei Darussalam.

Grouper is an important food fish due to its commercial value. A major production constraint in culturing grouper is that the fish can be fatally affected by leeches and diseases. Leeches are an ectoparasite of grouper, which can cause significant loss in fish number, and thus controlling their prevalence is indispensable as a tool of aquaculture management. In order to understand the prevalence and infestation intensity of a piscicolid leech Zeylanicobdella arugamensis, field observation of hybrid grouper was conducted in two aquaculture farms in Brunei Darussalam. The prevalence rates were 100% for the two farms throughout the study period, while the infestation intensity levels were significantly different between the two farms. The farm with the higher salinity ranging from 26 to 28 psu was found to have a significantly higher number of leeches (505 ± 271 leeches fish-1; mean ± SD) than the other farm with the lower salinity ranging from 17 to 23 psu that had 27 ± 23 leeches fish-1, although the ranges of recorded water temperatures overlapped between the two farms. This study suggests salinity might be an important factor in the propagation of Z. arugamensis. Furthermore, the prevalence and intensity of the leech in Brunei Darussalam were higher than those reported in other Southeast Asian countries. These results indicate that the hybrid grouper culture in Brunei Darussalam might have a higher risk in disease than those countries.