Social organization forms in fish groups have been very poorly studied. However, NELISSEN (1985)
found that Melanochromis auratus (BOULENGER, 1897) establishes linear rank orders in
aquarium tanks. This Mbuna cichlid (Lake Malawi) is closely related to all other species of the
ten Mbuna genera (RIBBINK et al., 1983) belonging to the very complex community (Mbuna is a
community of a monophyletic species flock; FRYER and ILES, 1972). After this study the question
arose whether other Mbuna cichlids have the same kind of social organization. In order to find
out about this a study of M. johanni (ECCLES, 1983), Pseudotropheus
« ornatus » (not yet described) and P. lombardoi (BURGESS, 1979) was
carried out. A few groups of M. auratus were also observed in order to make a comparison
between the four species. Individuals of the same species were kept in groups of 3 to 6 members.
The colour patterns and their changes were described, the length of the individuals was measured
and the agonistic acts (full display, chasing, circle fighting, mouth fighting, quivering,
avoiding and fleeing) were recorded. These recordings of aggression and aggression inhibition
were converted into interaction matrices for analysis. All three species establish a linear rank
order in aquaria similar to the dominance hierarchy formed in groups of M. auratus (see
NELISSEN, 1985). In these rank orders interactions are ordered: - the interactions depend upon
the status of the animals in question. - neighbouring animals in the hierarchy interact more
frequently with each other then [sic] with other group members.