Metallothionein as an indicator of heavy-metal exposure in two subtropical fish species

Abstract

Induction of metallothionein (MT) and levels of cadmium, zinc and copper in liver of the subtropical fish blue-striped grunt Haemulon sciurus were studied after cadmium injection. Hepatic levels of MT, zinc and copper were also analysed in blue-striped grunt and tomtate H. aurolineatum caught at heavy-metal-polluted areas of Hamilton Harbour and Castle Harbour, Bermuda, respectively. In addition, a comparison of the hepatic content of MT, cadmium, zinc and copper was made between blue-striped grunt, tomtate and squirrelfish Holocentrus rufus, caught at unpolluted locations. Hepatic MT was assayed by a radioimmunoassay (RIA), using an antiserum raised against MT from perch Perca fluviatilis and partially purified MT from blue-striped grunt as standard. Hepatic MT was significantly ( P < 0.001) induced in a dose-dependent manner in response to a single i.p. injection of CdCl 2. The doses were 2200, 740, 250, 82, 27 and 0 μg Cd · kg −1 body wt, respectively. Significantly elevated hepatic MT levels ( P < 0.01) were found 2 days after injection of 2200 μg Cd · kg −1 body wt and maximum content of MT in liver was reached after 6 days. MT values in fish 6 days after treatment were increased five-fold compared to the control group. Significantly increased MT levels ( P < 0.05) were also found in livers of blue-striped grunt and tomtate caught at contaminated sites compared to control fish. The increased MT levels were in good accordance with the hepatic zinc and copper levels in these fish. The levels of MT, cadmium, zinc and copper in liver from blue-striped grunt and tomtate, caught at clean sites, were within the range found in other fish species, such as rainbow trout Oncorhynchus mykiss and P. fluviatilis. Squirrelfish, caught at an uncontaminated site, had exceptionally high levels of hepatic MT, zinc and copper.