This is an electronic version of an article published in The Journal of Fish Biology: complete citation information for the final version of the paper, as published in the print edition of The Journal of Fish Biology, is available on the Blackwell Synerg

This is an electronic version of an article published in The Journal of Fish Biology: complete citation information for the final version of the paper, as published in the print edition of The Journal of Fish Biology, is available on the Blackwell Synergy online delivery service, accessible via the journal's website at http://www.blackwellpublishing.com/JFB or