The influence of chemical cues on the territorial prior residence effect in convict cichlids (cichlasoma nigrofasciatum Günther)

The importance of accumulated chemical cues on the occurrence of the territorial prior residence effect was investigated in two experiments using adult convict cichlids (Cichlasonul nigrofasciatum). In the first experiment, pairs of fish, matched on a number of criteria, were randomly assigned to three independent treatment conditions in which (1) the territorial marker (pot or clump of plants) was removed just prior to a direct encounter in the aquarium of the resident (pair member in whose aquarium the encounter took place) with accumulated chemical cues remaining intact; (2) the marker was removed, as well as the chemical cues; or (3) the marker was present, but the chemical cues were removed. Results showed that a significant prior residence effect occurred when the marker was present, but did not occur in either condition in which the marker was removed. A second experiment, in which the marker was removed and the gravel substrate altered, also did not reveal a signficant prior residence effect. Apparently, the territorial resident recognizes his territory by using certain visual cues, with accumulated chemical cues being neither necessary nor sufficient in this process.     

Maternal aggression during the mouthbrooding cycle in the Cichlid fish,Oreochromis mossambicus

Maternal aggression was studied in Oreochromis mossambicus during the mouthbrooding cycle. Brooding females were observed in heterosexual captive groups, and their agonistic interactions and behavioural activities were registered. Brooding females were classified into three classes according to the developmental stage of the brood they were incubating: phase 1, brooding eggs; phase 2, brooding fry with yolk-sac; phase 3, brooding fry with exogeneous feeding. The behaviour of the brooding females was compared with the behaviour of control non-incubating females. During the brooding cycle females become increasingly more aggressive toward other individuals, with their aggressiveness reaching a peak in phase 3. During the brooding cycle the females also suppress their feeding activities. The outcome of the agonistic interactions (victories–defeats) of the brooding females was positively correlated with the brooding phase but not with clutch size. The main function of maternal aggression in O. mossambicus seems to be the defence of the vulnerable brood against predators, including conspecifics, at a developmental stage when the fry start to forage outside the mother's mouth. Aggr. Behav. 24:187–196, 1998. © 1998 Wiley-Liss, Inc.     

On the (in)stability of dominance hierarchies in the cichlid fish Oreochromis mossambicus

Dominance hierarchies were studied during 8 weeks in eight heterosexual captive groups of Oreochromis mossambicus at the onset of sexual maturity. Linearity was assessed for each group on a weekly basis based on the Landau's index (h) and on the procedure described by Appleby [Appleby MC (1983): Animal Behaviour 31:600–608]. Week-to-week stability of the hierarchical structures was measured using the Burk's stability index (b) and Spearman rank correlation coefficients for the ranks of fishes in consecutive weeks. The two measures of stability showed a high level of concordance but the Spearman rank correlations were more conservative in detecting cases of stability. Although most dominance structures were linear they were unstable from week to week. Dominant individuals were less likely to experience rank reversals than subordinates. Rank reversals were especially likely among hierarchical neighbors. Dominance hierarchies did not stabilize in the time span of this study. © 1996 Wiley-Liss, Inc.