Effects of Cadmium and Copper on Metallothionein Gene Expression in Nile Tilapia (Oreochromis niloticus)

Abstract

            Nile Tilapia (Oreochromis niloticus) is the economic aquaculture which is widely cultured in Thailand. Therefore, it is suitable as a test animal for detecting heavy metal contamination in natural waters. Metallothionein (MT) is a metal-binding protein and its expression is stimulated by essential metal as well as toxic metals. The purpose of this study was to compare cadmium and copper exposure at different concentrations and time periods on expression of MT gene in tilapia. Fish were exposed to cadmium (0.25 and 2.50 μg/L) and copper (25 and 250 μg/L) for 1, 2, 4 and 8 hrs. Liver tissues were collected at each time point for total RNA extraction. Subsequently, first strand cDNA was synthesized
and used as template in the PCR reaction. Expression of MT gene was detected using RT-PCR technique. Results indicated that gene expression was induced within 1 hour of exposure to cadmium (0.25 μg/L), while that for copper
exposure (25 μg/L) was 2 hrs. In conclusion, MT gene can be used as biomarker for detecting cadmium and copper contamination in natural waters. MT expression is more sensitive to cadmium than copper exposure.