Reproductive Strategies of Zooplanktivorous Haplochromine Cichlids (Pisces) from Lake Victoria before the Nile Perch Boom

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Abstract
Due to the introduction of the Nile perch (Lates niloticus) into Lake Victoria the selection pressures imposed on both juveniles and adults of haplochromine species (Haplochromis spp.) have drastically changed. In this paper we describe the reproductive strategies of zooplanktivorous haplochromine cichlids occurring in the Mwanza Guld of Lake Victoria before the Nile perch boom. Five species were studied: H. pyrrhocephalus, H. heusinkveldi, H. "argens", H. laparogramma and H. piceatus. In addition, less complete data on a sixth species. H. "reginus", were collected. A matrix, comprised of 19 variables was analysed by mutli-dimensional scaling (MDS) and cluster analysis. The following trend was discovered: greater interspecific distances in the MDS configuration, e.g. more different reproductive characteristics, were associated with larger interspecific overlaps in taxonomical characteristics. Interspecific differences were found in body size of sexually active individuals, in absolute and relative fecundity, egg size, gonadosomatic indices, timing of the breeding period, location of spawning sites, brooding sites and the distribution of juveniles. This is notable since these species are closely related endemics. The interspecific differences in reproductive characteristics are likely to contribute to the partitioning of resources. In addition, we found tentative evidence that H. heusinkveldi, H. pyrrhocephalus and H. laparogramma may have speciated without preceding divergence of the morphology of the trophic apparatus.