Although the Cichlidae is a well-studied family of African fishes, the evolution of sexual
size dimorphism (SSD) and its relation to life-history, behaviour, feeding and habitat have
not been comparatively examined. The investigation of SSD reported here was based on a
study of the scientific literature. Prerequisites to such studies are records of maximum
size of adult males and females. Disappointingly few authors published such measurements,
so the data are fewer than anticipated given that the cichlids are such a species-rich
group. Now that this omission has been noted, it is hoped that investigations of the future
will include information on maximum size of adults of both sexes. Data from 215 species
showed great variation in the degree and direction of SSD, without any really strong trends
being evident. In the majority of species, males were larger than females or there was no
size difference between the sexes. In 10% (21 species), females were larger than males.
All of these are lacustrine, tend to live in deep water often over muddy substrata and
to feed to a greater extent than expected on non-defendable food sources. The degree of SSD
increases with increasing body size in species where males are the larger sex and decreases
in species where females are the larger. In territorial species, in which competition between
territorial males is intensive, males are the larger sex. The expectation that polygynous
cichlids would show a more marked degree of SSD than monogamous species was not met. Larger
size in females (with one exception) occurs in mouthbrooding species only. Males are the
larger sex in substratum brooders. It seems that the degree and direction of sexual size
dimorphism in cichlids is a consequence of a balance of natural and sexual selection, but
there is a need to increase the sample size to understand the interplay of these selection
pressures and to establish the validity of the emerging trends.