An analysis of reproductive behavior in the mouthbreeding cichlid fish, Tilapia macrocephala (Bleeker).

Qualitative descriptions and quantitative measurements of the patterns of reproductive behavior of the African mouthbreeding cichlid fish, Tilapia macrocephala (Bleeker), have been presented. These patterns have been grouped into three categories. The first, namely courtship, includes head-nods, approach-throat-puffs, body-quivers and tail-slaps. Most the females exhibited these courtship items during the observation periods, and at a relatively high frequency. The males performed these courtship acts at a considerably lower frequency. A high percentage of males showed some tail-slaps and body-quivers, and it is believed that if the entire spans of the pre-spawning activity of the pairs could have observed, all of the males would have performed these courtship patterns. On the other hand, it appears that a measurable portion of males do not head-nod or approach-throat-puff prior to the spawning. It is hypothesized that courtship behavior is an expression of the level of excitability of the individual. It may be thought of as a trophallactic process which through mutual stimulation serves to regulate the behavioral activities and physiological processes of the male and female so that well synchronized spawnings result. Nipping, which is closely related to courtship and which also appears to be mutually stimulating, was performed equally by the male female before the spawning, but nipping on the part of the female rises sharply directly after oviposition. Similar post-spawning increases on the part of the female were noted for all of the courtship patterns. It is suggested that the physiological changes following oviposition plus the presence of eggs are the factors responsible for this heightened activity. During the inter-spawning interval, a low level of courtship is in evidence, especially on the part of the females. The second group of reproductive patterns includes those acts which are concerned with the immediate preparation for spawing. Included here are nest-building, nest-passing, spawning-quivers, oviposition movements and the act of fertilization. Considerably more nest-building is exhibited by the female than by the male, but it is likely that all males do some nesting-building before every spawing. With passing-nest and spawning-quivers the frequency is somewhat higher for the males an hour or so before spawning, but at 15 minutes before spawning this relationship is clearly reversed, with the females at the height of their nest-passing and spawning-quivers. A significant correlation between male and female nest-passing during the first pre-spawning interval suggests that this behavior is mutually stimulating. The mean number of oviposition movements of the female did not differ significantly from the mean number of fertilization acts of the male. Moreover these behavior patterns are highly correlated, suggesting that the number of times the male fertilizes the eggs is partly related to and probably dependent upon the number of oviposition movements of the female. In contrast with the courtship patterns, behavioral items in the present category were not observed during the inter-spawning interval. The third category of reproductive acts are those associated with the care of eggs and young. Males start picking up eggs on an average of 1'3" frm the beginning of oviposition. Females, if given the opportunity, took the average 7'59". This is the apportioning mechanism whereby males usually incubate the eggs and females do so only on infrequent or special occasions. Similar quantitative differences were found in other phases of the parental pattern. Thus females gather up the spawn more slowly and are more prone to swallow the eggs. A low order positive correlation was found between the size of the female and the number of eggs laid during a given spawning. Since brood size shows no correlation with the size of the female, it is concluded that a greater mortality occurs in the larger broods. Incubating fish generally carry some gravel intermingled with the spawn, but it was not clear whether this bore any relation to the survival of the embryos. In the majority of vertebrates there are distinct qualitative differences between the patterns of reproductive behavior of the male and female. While both sexes have the neuromuscular mechanism capable of eliciting both the male and female patterns, bisexual of homosexual behavior is limited and generally appears under special conditions. Tilapia are exceptional in this respect insofar as there are not distinct qualitative differences between male and female in their sexual activities. However, there are marked quantitative differences in all of the patterns. Several previous investigators have analyzed cichlid mating behavior in terms of Lorenz's releaser concept. it is felt that even in the expanded and modified form presented by Tinbergen, this concept is still too restricted to form an adequate basis for the analysis of Tilapia reproductive behavior.