Does Serranochromis altus (Teleostei: Cichlidae) exist in the Okavango Delta, Botswana?

Abstract

Two possibly synonymous fish species in the Okavango Delta, Botswana, Serranochromis altus and S. angusticeps, were compared. Ecological data, morphometrics, meristics, allozymes, and genomic fingerprints — generated with six Inter-Simple Sequence Repeat (ISSR) analyses, and DNA barcoding primers — were compared for both species and individuals with intermediate diagnostic characters. Serranochromis altus was the largest species, having the greatest number of anterior teeth rows, whereas S. angusticeps was the smallest with the lowest number of anterior teeth rows. The intermediate group, with overlapping characteristics, had intermediate body size and teeth row numbers. Morphometric comparisons of mass with the combined individuals' growth (standard length) showed a high positive correlation (r 2 = 0.873). Allozyme analysis of individuals revealed no fixed allele differences, minute differentiation (average F ST = 0.018) and high gene flow (NeM = 7.672) between the species. No hybrizymes were found. Allozyme data indicated that these 'species' are part of a single, panmictic population, which was confirmed by ISSR analysis and fish DNA barcoding. Genetic and interspecific divergence in allometry between S. altus and S. angusticeps were non-significant. It was initially thought that these fishes represented different life stages of S. angusticeps. However, we found fish of different sizes, yet with similar ages, representing both species. More accurate age/size and other molecular analyses are required in order to determine if these represent different life stages of S. angustiuceps.