NATURALLY HIGH-LEVELS OF ZINC AND METALLOTHIONEIN IN LIVER OF SEVERALSPECIES OF THE SQUIRRELFISH FAMILY FROM QUEENSLAND, AUSTRALIA

Recently, we found that liver of squirrelfish (Holocentrus rufus) from Bermuda contains remarkably high concentrations of metallothionein (M T) and Zn. To clarify the nature and cause of the Zn accumulation, fou r Holocentridae species from three genera (Neoniphon sammara, Sargocen tron spiniferum, Myripristis violacea, and Myripristis murdjan) were c ollected from a totally different area, the Great Barrier Reef, Austra lia. The average hepatic Zn levels in these species ranged from 67 mu gg(-1) (S. spiniferum) to 1000 mu gg(-1) (N. sammara). The intraspecie s variation in the hepatic Zn level was pronounced. In both N. sammara and M. murdjan, there was a 48-fold difference between the lowest and the highest Zn concentration. Zn accumulation was closely correlated to a dramatically elevated concentration of MT in liver. In N. sammara , which possessed the highest level of MT among the investigated speci es, the mean hepatic MT concentration was 19500 mu gg(-1). Subcellular fractionation of the liver showed that MT was responsible for the bin ding of up to 74% of the hepatic Zn. The concentrations of MT and Zn i n gills were low, suggesting that Zn storage in fish within this famil y is tissue-specific. The results further indicate that the high conce ntrations of MT and Zn in Holocentridae liver are linked to normal phy siological processes. We suggest that the Holocentridae family may be a unique model for future studies of Zn metabolism and the function of MT.