MEPS 138:41-49 (1996)  -  doi:10.3354/meps138041

The utility of fishes as biomonitors for mercury in aquatic environments is widely recognised, with skeletal muscle as the tissue normally chosen for most monitoring programmes. The liver may also be a suitable candidate tissue for monitoring, as it concentrates many pollutants to higher levels than muscle, and is closely involved with processes of metal dynamics, storage, and detoxification. Little consideration has been given previously to the validation of the use of liver for mercury biomonitoring, with regard to quantifying natural temporal variation. This study considered such variation in the eelpout Zoarces viviparus L., a resident estuarine fish species collected from a subtidal site near a formerly major industrial mercury discharge in the Forth Estuary, eastern Scotland. Liver and skeletal muscle mercury concentrations, liver weight, and body size variables were measured for 196 individual eelpout in seven 3-month periods. Liver Somatic Index (LSI) was significantly higher, and liver mercury concentrations significantly lower, in the summer than in other seasons. Liver mercury burden (the mass of liver mercury per fish), in contrast, showed only limited significant seasonal variation relative to body size, implying that the observed seasonal variation of liver mercury concentration (by around a factor of 3 between summer and winter) results largely from the dilution of similar burdens by a seasonally growing and shrinking liver. Such natural seasonal variation may confound the use of the muscle/liver mercury concentration ratio, which has been proposed as evidence of fish migration between waters with different levels of mercury contamination. These results also suggest that, as variation in liver mercury concentrations is closely related to seasonal variation in LSI, liver tissue may not be a reliable monitor for mercury in temperate species of marine fishes with seasonally fluctuating liver size.

Mercury . Biomonitoring . Liver . Fishes . Zoarces viviparus . Forth Estuary, Scotland