Abstract:
Acute toxicity and subacute toxicity of the heavy metal, cadmium, on the
expression of metallothionein mRNA (MTmRNA) in livers and kidneys of silver carp,
Puntius gonionotus were studied for 96 hours and 3 months, respectively.
The results showed that the LC50 values of cadmium at 24-h, 48-h, 72-h and 96-
h were 3.81, 3.41, 3.23 and 2.88 mg/L, respectively. Based on these values, the selected
subacute concentrations used in this study were 0.012, 0.06 and 0.12 mg/L. The
MTmRNA expression in cadmium-treated fish was monitored at 2, 5, 7, 14, 21, 28, 35,
42, 49 and 56 days of cultivation. Thereafter, the fish were moved to cadmium-free
water and MTmRNA level was monitored again at 63, 70, 77 and 84 days of
cultivation. The expression of MTmRNA in the liver was likely to correlate with the
exposure time whereas that in the kidney was preferentially correlated with cadmium
concentrations. The maximum levels of MTmRNA in both liver and kidney were
obtained during 28-35 days. At 0.012, 0.06 and 0.12 mg/L of cadmium, there were 4.20,
4.43 and 4.93 fold increases of the MTmRNA in the livers and 4.16, 3.34 and 5.57 fold
increases in the kidneys, respectively. The levels of MTmRNA expression in both liver
and kidney were slightly increased between days 63 and 84. The increase of MTmRNA
in silver carp after exposure to cadmium might be important for cell viability. This may
be due to the ability of metallothionein gene product to bind to excess cadmium
accumulated in liver and kidney and to reduce the toxicity to fish. The long-term effect
of cadmium in the liver of silver carp on MTmRNA expression offers a possible use of
MTmRNA as a biomarker for the assessment of heavy metal contamination in the
environment.