EROD in fish liver

 EROD activity in fish liver can serve as an early warning of environmental damage

Ethoxyresorufin-O-deethylase (EROD) is a detoxification enzyme (Cytochrome P450) induced in some contaminants-affected organisms as a defence against toxic chemicals in the environment. Usually, fish caught from polluted areas have higher EROD activity than those from unpolluted waters. Measurement of EROD activity in fish liver is a well-established biochemical biomarker of exposure to polycyclic aromatic hydrocarbons (PAHs) and organochlorines, including polychlorinated biphenyls (PCBs) and dioxins. The levels of EROD activities generally represent the cumulative impact of all inducing chemicals in water, sediment and tissue, whether or not they are detected analytically. It is one of the first detectable, quantifiable responses to exposure. For this reason, EROD is often used as an early warning of environmental damage. 

The rabbit fish Siganus oramin	The pony fish Leiognathus brevirostris

Two fish species were used for the analysis of EROD activities, i.e. the rabbit fish Siganus oramin and the pony fish Leiognathus brevirostris. EROD activities of the two species recorded in 2004 (S. oramin: 14-106 pmol/mg/min; L. brevirostris:13-21 pmol/mg/min) were generally higher than those obtained in 2005 (S. oramin:19-44 pmol/mg/min; L. brevirostris: 5-14 pmol/mg/min). The levels of EROD activities obtained from the rabbit fish S. oramin (14-106 pmol/mg/min) were higher than those from the pony fish L. brevirostris (5-21 pmol/mg/min). Spatially, EROD activities in these fish were generally higher in Zone 4 in Port Shelter & Outer Mirs Bay than other waters. The body burden of PCBs were higher in both fish species collected from Zone 6 (Victoria Harbour & Junk Bay); while the body burden of PAHs were generally higher in fish obtained from Zone 3 (Tolo Harbour & Inner Mirs Bay). Overall, no clear relationship between EROD activity and the levels of PCBs/PAHs in the target fish species was found in 2004 and 2005.

Table: EROD activities in the two fish species at various sampling zones in Hong Kong waters.