The form, function and phylogenetic significance of the vomero-palatine organ in cyprinid fishes

Abstract

Summary The vomero-palatine organ is a peculiar fleshy structure which occurs on the buccopharyngeal roof of 15–20% of cyprinid fish species. Researchers have advanced three main hypotheses for the function of the organ: respiratory, sensory and trophic. From a study of comparative biology a trophic function is most likely, but there are points in favour of the two remaining ideas. It is suggested that the organ is primarily concerned in bolus-formation by the active co-mixing of precipitating mucous secretions with ingested particles (food and sediment). Comparative studies also show the organ to be of taxonomic use. It is a shared specialization (synapomorphy) which unites the labeine group it characterizes. The vomero-palatine organ is found in a regressed state in rheophilic algae-scraping species of Labeo and Garra. Using standard cladistic arguments and ecological data on feeding habits, it is suggested that this regression is a derived condition (autapomorphy) which has evolved independently in the...