Interestingly, we could find only one leptin receptor (lepr) gene in zebrafish, or indeed in any currently available teleostean genome we screened, including the very well annotated genomes of medaka, Tiger pufferfish and Green-spotted pufferfish (Gorissen et al., 2009), so the question remains if these leptin paralogues have different signalling capacities through a single type of leptin recep tor. The vast difference in amino acid sequence between leptin-a and leptin-b, combined with the leptin receptor-binding properties (i.e. one binding site for leptin molecules), makes it difficult to envisage this mode of signalling. Indeed, when the binding energies of zebrafish and medaka leptin-a and leptin-b, bound to the leptin receptor of each species are calculated, the binding energy of leptin-a is considerably higher than that of leptin-b (Prokop et al., 2012). Possibly, an as yet unknown receptor