Maternal transfer of cadmium tolerance in larval Oreochromis mossambicus

Exposing female tilapia to Cd did not affect reproduction and egg quality, nor the survival of their offspring. The LT ₅₀ of Cd-exposed larvae (within 24 h post hatching) from Cd-treated female Oreochromis mossambicus (mean ±S.E.=10·9±0·5 days, n =4) was greater than that of Cd-exposed larvae from control females (6·9± 1·2 days, n =4). A substantial amount of metallothionein mRNA (MT mRNA) was found in both oocytes and newly hatched larvae from Cd-treated females, but MT mRNA levels were low in newly fertilized eggs. The amount of MT mRNA was very low in all these stages in the control group. Cadmium could not be detected at any stage for either control or Cd-treated group, and metallothionein protein levels were also very low in both groups. The early appearance of MT mRNA in oocytes and newly hatched larvae from Cd-treated females may result in early translation after hatching and explain their tolerance to Cd.