Intraspecific morphological variation among a population of Haplochromis nyererei
(Teleostei, Cichlidae) from Lake Victoria was investigated. Three main groups of variables
were used: general shape, outline of the head, and trophic group (intestinal length,
stomach contents, teeth and jaw shape, lower jaw length and width). Fishes were arranged
into four groups: G1, large males with a prominent bump on the head, a thickset body and
anatomical structures related to a strictly insectivorous diet; G2, large males lacking a
bump on the head but more or less thickset and showing anatomical structures related to
omnivorous feeding habits, though favouring insects; G3, males and a few females with a
slight bump on the head, a slender body shape and showing anatomical structures related
primarily to a herbivorous tendency; and G4, females and a few small males without a bump
on the head, a slender body and showing anatomical structures related to an omnivore with
herbivorous tendencies. Several hypotheses related to behaviour are presented partly to
explain the intraspecific variation observed. Differences between individuals could arise
as a result about the establishment of dominance and territory in males.