Ascorbic acid biosynthesis in Amazonian fishes

Abstract The incapacity to synthesize ascorbic acid (AA) is due to the lack of activity of l -gulonolactone oxidase (GLO), which catalyzes the last step of AA biosynthesis. It was postulated that vertebrates unable to synthesize AA had sufficient amounts of this nutrient in their diet and consequently did not need to preserve synthetic capability. In the present study, we analyzed the GLO activity in kidney and liver of 13 fish species, including 11 teleosts, namely: freshwater stingray, Potamotrygon sp.; South American lungfish, Lepidosiren paradoxa ; “sardinhao,” Pelona sp.; arowana, Osteoglossum bicirrhosum ; arapaima, Arapaima gigas ; “piranha caju,” Pygocentrus nattereri ; “piranha mucura,” Serrasalmus elongatus ; “aracu,” Schizodon fasciatus ; “tambaqui,” Colossoma macropomum ; “acari-pedra,” Hypostomus sp.; “sarapo,” Steatogenys elegans ; electric eel, Electrophorus electricus ; and the peacock bass, Cichla sp. Four representatives of the Characiformes order with distinct feeding habits were included in this study to evaluate the influence of feeding habit on GLO activity. Only two species of non-teleost fishes, the freshwater stingray (Miliobatiformes) and the South American lungfish (Lepidosireniformes), showed GLO activity in their kidneys, corroborating the hypothesis that teleosts are unable to synthesize AA. Additionally, as expected, we observed that the phylogenetic position is more important than feeding habit as a determinant of the biosynthetic ability since none of the Characiformes species analyzed synthesize AA, independent of their distinct feeding habits. Female freshwater stingrays had a significantly higher GLO activity than males ( P P >0.05), as previously reported in white sturgeon. This is the first report of the AA biosynthetic ability in South American lungfish and freshwater Elasmobranchs.