Muscle fatty acids as indicators of niche and habitat in Malawian cichlids

Fatty acid composition in the muscle of eight endemic haplochromine cichlid s and one tilapiine cichlid from Lake Malawi was studied by gas-liquid chro matography. The species studied represent a wide variety of niches: Algae c ombing, shell crushing, feeding on littoral and semipelagic zooplankton, de tecting invertebrates hidden in the sediment using expanded lateral line ca nals, and fish predation in littoral and bathypelagic zones. The sampling w as done during the early rainy season. The analysis of fatty acid compositi on suggests that, despite the reported plasticity in feeding, the niches of the species studied are established and stable. The proportion of eicosape ntaenoic acid (20:5n-3) in relation to arachidonic acid (20:4n-6) illustrat ed the position of these species in the foodweb: equal proportions in algae feeders and clear 20: 4n-6 dominance in species feeding on benthic prey. A lthough the number of replicates was small, discriminant analysis with 31 f atty acids separated the specimens into dense centers according to species. These results encourage the use of chemometric methods for studying ecolog ical relationships among freshwater fauna and ongoing evolutionary processe s.