Water quality and biotic interaction of two cavefish species: Typhleotris madagascariensis Petit, 1933 and Typhleotris mararybe Sparks & Chakrabarty, 2012, in the Mahafaly Plateau groundwater system, Madagascar

The karstic subterranean aquatic system of the Mahafaly Plateau in south-western Madagascar is inhabited by two species of cavefish: Typhleotris madagascariensis and Typhleotris mararybe. Knowledge about both cavefish species is scant. In order to learn more about the distribution of the two species, 15 caves and sinkholes spread over the Mahafaly Plateau were inventoried for their presence. Abiotic water quality and interspecific relations of the two species were investigated in six of these caves and five of the sinkholes during the dry and the rainy seasons. Typhleotris madagascariensis was present in all sampled water bodies while T. mararybe was restricted to five sites in the region around the town of Itampolo. The inventories extend the known range of both species of Typhleotris on the Mahafaly Plateau. Abiotic water characteristics did not differ between seasons. The abundances of both species were negatively correlated with iron concentrations. Further correlations between the abundance of either fish species and abiotic water characteristics remained inconclusive as these water characteristics co-varied with geographical latitude that in turn was correlated with fish abundance. For both species neither the abundance nor a condition factor based on body mass showed any significant seasonal variation. Also the presence of T. mararybe had no influence on the abundance and the condition of T. madagascariensis. Thus, no evidence for competition was noticed between the two species.