of the large family of type-I a-helical cytokine receptors acts downstream of one of the two leptin paralogues, or their actions are regulated on yet another level. Prokop et al. (2012) suggest that the multiple leptins found in fish may bind to the leptin receptor through altered hydrophobic interactions in a temperature related manner; an attractive hypothesis, since fish are ectotherms and thus their biochemistry is subjected to fluctuations in water temperature, and fluctuations in body temperature. Binding assays with leptin receptor and homologous recombinant leptin-a and leptin-b will elucidate whether both leptins act as ligand for the same leptin receptor, or that scenarios exist for leptin signalling in fish.