Diel fluctuations in blood metabolites in cannulated African catfish (Clarias gariepinus, Burchell 1822)

Abstract

African catfish were cannulated in the dorsal aorta to study diurnal changes in blood metabolites. Cannulation of the branchial artery was tested but proved to be less successful. A clear diel fluctuation in the two major blood metabolites, free fatty acids (FFA) and glucose, was observed. Compared to the initial value at 8.30 a.m., the plasma FFA levels dropped by ca. 50% within 2 hours, after which the FFA concentration stayed relatively constant. Minimum values of 0.26±0.04 mM were reached at 12.30. The FFA concentration recovered to the initial value within the following 3 hours. The fluctuation in plasma glucose levels showed a comparable course but there was a phase-shift by 2 hours. The most astonishing finding of our study was the almost complete absence of glucose in the plasma of African catfish (0.05 ± 0.03 mM), a never reported phenomenon for any fish species. This study demonstrates the relatively low level of control of plasma glucose levels as compared to plasma FFA levels in African catfish.

Beta-adrenergic control of plasma glucose and free fatty acid levels in the air-breathing African catfishClarias gariepinusBurchell 1822

“…The infusion of saline induced a significant decrease in plasma glucose and FFA levels in African catfish, which reflects a circadian fluctuation in both metabolites (Van Heeswijk et al, 2005). Comparable circadian fluctuations in blood metabolites have been reported for numerous other fish species (see review by Boujard and Leatherland, 1992).…”