Certification is an increasingly pervasive form of market governance through which retailers and NGOs are able to exert control over producers of primary products in order to secure their commercial and institutional interests. This paper assesses the likely outcomes of emerging certification standards intended to govern production of a new global commodity, Pangasius catfish. This evaluation focuses on Pangasius producers in Vietnam and Bangladesh, and one of the key areas which standards seek to regulate; the environment. We conclude that certification is likely to result in greater differentiation and polarisation between larger and smaller farm operators and will increasingly act to exclude of the latter from access to Western European and North American markets, and that any local environmental gains produced may be of relatively minor significance.