Arsenic (As) is a major hazardous metalloid in many aquatic environments. This study quantified the biotransformation of two inorganic As species [As(III) and As(V)] in a marine juvenile grunt Terapon jarbua following waterborne and dietborne exposures for 10 d. The fish were fed As contaminated artificial diets at nominal concentrations of 50,150, and 500 As(III) and As(V)/g (dry weight), and their transformation and growth responses were compared to those exposed to 100 mu g/L waterborne As(III) and As(V). Within the 10 d exposure period, waterborne and dietborne inorganic As exposure had no significant effect on the fish growth performance. The bioaccumulation of As was very low and not proportional to the inorganic As exposure concentration. We demonstrated that both inorganic As(III) and As(V) in the dietborne and waterborne phases were rapidly biotransformed to the less toxic arsenobetaine (AsB, 89-97%). After exposure to inorganic As. T. jarbua developed correspondingly detoxified strategies, such as the reduction of As(V) to As(III) followed by methylation to less toxic organic forms, as well as the synthesis of metal-binding proteins such as metallothionein-like proteins. This study elucidated that As(III) and As(V) had little potential toxicity on marine fish. (C) 2012 Elsevier B.V. All rights reserved.