The standard length, diurnal activities, territory sizes, and areas over which individuals
foraged and the nutritional condition of territorial and non-territorial Cynotilapia afra
and Pseudotropheus zebra were compared. Results show that territorial tenureship in
these fishes does not depend on the male size, implying that aggressiveness, experience and
motivation are more important in the maintenance of territory. However, territoriality in
C. afra (t = 10.93, P < 0.05) and P. zebra (t = 3.31, P < 0.05) manifests
itself in the reduction of nutritional condition because territorial males engage in
energetically more demanding activities, e.g. courtship displays, fertilizing ripe females
and chasing intruders that trespass into their territories. Territorial C. afra
(t = 4.77; P < 0.05) and P. zebra (t = 5.89; P < 0.05) also fed over significantly
smaller areas and spent significantly less time feeding than did non-territorial males.
The biological significance of territoriality in these fish species is therefore not food
intake, but mate attraction and reproductive success for which they trade off their
nutritional condition. However, there might be a nutritional threshold below which the cost
out-weighs the benefit. Hence, territorial males in poorer health abandon their territories
in order to regain their condition.