Bile salts of fishes collected on the Zaïre River Expedition (1974-5): their chemical nature and its possible significance

Abstract

Bile salts from 21 fish species caught during the Zaire River Expedition (1974–5) have received partial or complete chemical analysis. Conclusions from the results are as follow. (1) Polypterus bile salts are biochemically advanced, but with easily detectable features regarded as relicts from ancestral stock. The bile acids include haemulcholic acid, previously found only in a marine teleost and an unidentified acid also found in a mormyrid. (2) This mormyrid has advanced bile salts, consisting almost entirely of taurine conjugates of haemulcholic acid (present in Polypterus), and two other C24 acids. (3) Three Alestes and three Distichodus species have no more than traces of primitive bile salts; their bile acids suggest a degree of activity of intestinal microorganisms during the enterohepatic circulation not previously noticed in fishes. (4) The predatory Hydrocynus has bile acids of an omnivorous rather than a carnivorous type. (5) The Barbus species have primitive bile salts closely similar to those of Cyprinidae previously examined but containing also (in two species) a newly-discovered bile alcohol sulphate: in contrast, a Varicorhinus does not have this new substance and has a chief bile salt found so far only as a minor constituent in the Cyprinidae. (6) Two Labeo species are different from all other cyprinids examined: diey both have a new major bile alcohol sulphate. (7) Four Siluriformes show evidence of enterohepatic changes that might be characteristic of some tropical freshwater fish; three have taurine-conjugated haemulcholic acid. (8) Synodontis species are remarkable in having a high proportion of unconjugated bile acid ions and this finding was confirmed with fresh material.