However, also the duplicate leptin genes described within a fish species may be so extraordinarily different in primary amino acid sequence conser- vation (e.g. in zebrafish these genes share only a mere 24% amino acid identity) that it is hard to imagine that these leptin genes did not acquire different functionality and are only redundant. Indeed, the fact that they still exist and (one of the paralogues) have not gone lost is testament to their non-redundancy.