The purpose of this study was to identify the factor(s) which would enhance the Cd resistance as assessed
by the metallothionein (MT) expression in tilapia larvae. Larvae were collected from parents that were
pretreated respectively with Cd or saline. At the end of the 12-week experiment, the hepatic MT and Cd
contents in the breeding female fish were recorded. Our results indicated that a significant relationship
between Cd and MT contents can be found in the offspring from the parent fish treated with Cd. However,
the higher Cd resistance, Cd contents, and MT expression were limited to those larvae from parent fish
bred within 4 weeks of the injection. By week 12, the Cd-treated fish still contained high levels of MT
in their hepatic tissues. However, the MT and Cd contents in the larvae from these adult fish were not
significantly different from those from the controls. In summary, we suggest that the higher Cd resistance
of larvae from the egg stage was a result of the Cd contamination of the parent female, as evidenced by
an increase in MT expression induced in tilapia embryos and larvae
