An ecomorphological explanation is given of the anal spots of haplochromine cichlids from
Lake Victoria. Anal spots are ovoid orange-yellow spots on the anal fins of these fishes.
The possible roles of sexual selection and predation as determinants of the form of these
spots are discussed. Evidence is given that the anal spots are egg mimics and thus examples
of intra-specific mimicry. Mimicking an egg to stimulate sexually active females presumably
is an important demand on the form of the anal spots. However, no positive correlation was
found between anal spot size and egg size. Light intensities of the habitat of the species
investigated showed a negative correlation with anal spot size. In contrast to this, egg
size did not show a negative correlation with light intensities. It is suggested that,
besides mimicry, at least one more demand is involved in determining spot size: that of
being conspicuous. Conspicuousness is likely to have a positive impact (benefits) on
courting conspecific females, but a negative one (costs) with regard to predators who
hunt visually for either adults or eggs. The actual appearance of anal spots may be a
compromise. This may explain the mismatch between egg size and spot size in many species.
Qualitative evidence is presented that predation pressures on adult haplochromines exerted
by visually hunting predators are relatively high in lighter habitats, viz. near the rocks
and near the surface. An alternative hypothesis that spots in dark surroundings cannot be
seen unless they are supra-normal is discussed.