Biochemical and physiological evidence that bile acids produced and released by lake char (Salvelinus namaycush) function as chemical signals

It has been hypothesized that faeces of juvenile lake char (Salvelinus nama ycush) may contain chemical cues that mediate behaviour of conspecifics. Ho wever, our knowledge of bile acids naturally produced and released by fish is limited. Using HPLC, we fractionated bile acids produced and released by lake char and examined their stimulatory effectiveness using electro-olfac togram recordings. Taurocholic acid, taurochenodeoxycholic acid, taurooxoch olanic acid, taurooxodeoxycholic acid 3 alpha -sulphate, trace amounts of t aurolithocholic acid and an unidentified sulphated bile steroid were found in bile and faeces. Bile acids were either taurine amidated or sulphated, o r both. Lake char released an average of 4 nmol min(-1) bile acids per kilo gram of body weight into their tank water. Urinary bile acids accounted for only a small portion of total bile acids released into water. Water and fa eces contained higher proportion of taurochenodeoxycholic acid and sulphate d bile acids (relative to taurocholic acid) than bile. The electro-olfactog ram recordings demonstrated that bile acids released by lake char were dete ctable by their olfactory system at nanomolar concentrations, which is well below the levels of bile acids released into water. The exquisite olfactor y sensitivity of lake char to water-borne bile acids released by their cons pecifics is consistent with a role for these compounds as important chemica l signals.