Pairs and Harems in a Cichlid Fish,Lamprologus brichardi1

L. brichardi is a substrate brooding cichlid with facultative polygamy. The social organization was studied in the field for a 6-week period. The mating structure was examined in detail in the laboratory. Two types of social groupings are described:

• 1 Aggregations of sexually mature but nonterritorial fish, also frequently visited by territory holders in the vicinity.
• 2 Reproductive units (families) mainly consisting of the reproducing pair members and offspring from several broods. All family members defend a common territory around the shelter site. Occasionally a male has access to two females each with a separate territory (harem).

The factors influencing mating structure were investigated in the laboratory:

• 1 Females select breeding sites rather than partners.
• 2 Without competitors for breeding sites, and with an equal or nearly equal sex ratio, harems were established nearly as often as pairs.
• 3 Young males are physically able to mate and form a harem; but they are usually prevented from doing so by more competitive (larger) males.
• 4 Competition for breeding sites is not a prime influence on harem formation, although it is of great importance in determining the composition and size of the breeding population.
• 5 Just as many pairs as harems were formed with and without predators, even though, with predators, no young survived.
• 6 In L. brichardi the formation of harems is not predominantly determined by the distribution of suitable spawning sites. The monopolization of females is only slightly influenced by the distance between their territories.
• 7 In L. brichardi it is not necessary for harem formation that the male is bigger than the female.
• 8 Behavioural protocols and data on growth rates, as well as spawning intervals, did reveal any consistent difference between pairs and harmes.

Of the variables tested, male competition for females was therefore the sole determinant of who should mate.