Metallothionein Induction in Early Larval Stages of Tilapia (Oreochromis mossambicus)

Amounts of whole‐body metallothionein (MT) in tilapia (Oreochromis mossambicus) larvae increased to a peak (1,500 ng mg−1 protein) 1 d after hatching (H1), decreased rapidly thereafter, and was maintained at a constant level (700 ng mg−1) 3 d after hatching (H3). Waterborne Cd2+ could stimulate MT expression in newly hatched (H0) larvae in dose‐dependent and time‐dependent patterns. H0 larvae, which were treated with 35 &mgr;g L−1 Cd2+ for 24 h, showed a 1.7‐fold increase in the MT amount ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $$174.0\pm 64.7$$ \end{document} ) and a 6.5‐fold increase in accumulated Cd2+ but no significant change in Ca2+ content, compared with the H0 control (MT, \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $$102.6\pm 48.1$$ \end{document} ). H3 larvae with the same treatment revealed about a 10‐fold increase in accumulated Cd2+, a 10% decrease in Ca2+ content, but no change in MT ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $$261.2\pm 120.0$$ \end{document} ), compared with the H3 control (MT, \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $$330\pm 74.0$$ \end{document} ). H0 larvae could synthesize more MT to bind Cd2+ for detoxification in 35 &mgr;g L−1 Cd2+, a dose that would not affect normal physiology or survival of H0 larvae. On the other hand, 35 &mgr;g L−1 Cd2+ caused H3 larvae to experience hypocalcemia, an abnormal physiological condition, in which H3 larvae could not synthesize sufficient MT, thus causing greater than 25% mortality. These results indicate for the first time that the inducibility of MT by waterborne Cd2+ is development dependent, being correlated with inconsistent sensitivities to Cd2+ during larval development.