Cichlids derive their popularity mainly from the care they bestow on their offspring. The brood care technique is not similar in all cichlids. There are substrate brooders, cave brooders, pit brooders, and mouth brooders. The most advanced form of brood care, livebearing, is not found in any cichlid species. According to a recent publication by Professor E.K. Balon (1991) there are ample indications that the evolution of livebearing cichlids is just a matter of time: "Speculatively, given time, the evolution of livebearing cichlids can be expected". It appears that this author sees the cichlids on an evolutionary trajectory, which starts at substrate brooding and ends at livebearing.
It is reasonable to assume that further improvements in brood care can only increase the success of cichlids. However, Jensen (1990) disagrees with this point of view. According to Jensen the cichlids belong to the suborder Labroidei. The labroid families in general are very rich in species. Jensen ascribes this richness to the pharyngeal specializations that occur among these fishes. The surf perches, Embiotocidae, however, are an exception. Although these labroids also display all the pharyngeal specializations that are so characteristic of the suborder Labroidei, they have failed to develop a species-rich family. In fact the surf perches are a species-poor fish family. Interestingly it is also the only labroid family which is livebearing. But livebearing is not the only feature in which the surf perches differ from other labroid families; it is thus not correct to ascribe their meagre speciation to the fact that they are livebearing (Jensen, 1990). Jensen's publication, however, makes it clear that labroid fishes can develop livebearing species, which puts Balon's ideas regarding the evolution of the cichlid's brood care in another perspective. Jensen further indicates that the success of cichlids would not necessarily be increased when they reached the livebearing stage.
Balon (1991) voiced his remarkable idea in a book which is entirely devoted to the coelacanth (Latimeria chalumnae). The coelacanth, probably the most talked about living fossil, is a fish with a truly remarkable breeding technique. Females of this species produce very large eggs which develop inside the reproductive system of the mother. Not all embryos develop at the same speed. Those that free themselves from the eggshell first feed on their large yolk-sac before they fall upon the embryos which are still in a earlier phase of development (oophagy or adelphophagy). As a result of this breeding technique the coelacanth produces few offspring, but the young are born well developed and thus have an increased chance of becoming mature.
In order to explain the origin of this breeding biology Balon refers to some cichlids from Lake Tanganyika. He discusses four Tanganyika cichlids, which he assumes to have a common ancestor. It seems that Balon regards the species flock of Lake Tanganyika as a monophyletic (developed from a single ancestor) which is most probably incorrect. Virtually all scientists share the opinion that the Tanganyika flock has a polyphyletic group (developed from several ancestors) origin, and this was recently confirmed by Nishida (1991). The common ancestor referred to by Balon must therefore have lived before the formation of the lake.
The cichlids which participate in Balon's investigation are: Boulengerochromis microlepis, Haplotaxodon microlepis, Tanganicodus irsacae and Cyphotilapia frontosa. Balon gives the breeding biology for these species as, respectively; a sandnest brooder, a pit brooder which "... guards its clutch in a sand-pit nest but after hatching collects the embryos into its buccal pouch and broods them" (i.e. larvophilous mouth-brooder; see remarks later), further a biparental mouth-brooder, and a maternal mouth-brooder.
B. microlepis produces an enormous quantity of small eggs. The hatched fry start their oral feeding when they have attained a length of 8.4 mm. By contrast C. frontosa, like the coelacanth, produces relatively large eggs but in small quantities. The eggs are brooded inside the female's mouth for more than 50 days (according to Balon). When the fry are released they have a length of 23.0 mm. Balon regards the breeding biology of H. microlepis and T. irsacae as intermediate stages between the sand nest brooding of B. microlepis and the maternal mouthbrooding of C. frontosa. Balon refers to Kuwamura (1988) when he describes the breeding biology of Haplotaxodon microlepis as being a larvophilous mouthbrooding. However, neither Kuwamura nor other authors have found H. microlepis or any other Tanganyika cichlid to be a larvophilous mouthbrooder.
Balon concludes from the breeding techniques of these four species that an intensification of the brood care leads to an increasing part of the early development taking place during the embryonal stage. Contrary to common practice he regards the end of the embryonic stage as being when the young start collecting their own food and not when they hatch from the egg. Young fishes which have freed themselves from the egg-shell but haven't started feeding orally are called "eleuthero-embryos" (free-swimming embryos). If we adopt this view then it appears that the larval stage in maternal mouthbrooding species is totally abolished in favor of an increased chance of growing into mature fishes. During the larval period the brood is very vulnerable. Moreover the transition from larva to juvenile demands a lot of energy. Such a reproductive biology (mouthbrooding) requires eggs with a high quality type of yolk. In general such eggs are also larger, but Balon (pers. comm.) finds it inappropriate to give too much attention to egg-size (see also table 1 in Kuwamura & Mihigo, 1988). The comparison of Tanganyika cichlids with the coelacanth does not seem to explain the latter's breeding biology. After all the coelacanth is a livebearer.
So how could a livebearing cichlid evolve? A necessary step is probably pelagic spawning, i.e. the eggs are released in midwater. The females collect the eggs before they have reached the substrate. This has been described for Copadichromis chrysonotus (see: Eccles & Lewis, 1981), Rhamphochromis sp. (Spreinat, 1991), and Cyprichromis sp. (Konings, 1991). The fertilization of the eggs of midwater spawners should take place immediately after they have been released and not in the female's mouth after they have been retrieved. According to this scenario the fertilization would take place in close proximity to the female's genital pore. As Balon has pointed out the female invests more and more in the quality of the eggs. A logical consequence is that the number of eggs decreases. In the end each and every egg is of importance for the survival of the species. This could then be a reason for females to tend to retain the eggs in their reproductive tract while males exude their milt in the immediate vicinity of the female's genital pore. Eventually this could lead to livebearing cichlids.
- Balon E.K.; 1991; Probable evolution of the coelacanth's reproductive style; lecithotrophy and orally feeding embryos in cichlid fishes and in Latimeria chalumnae. Env. Biol. Biol. Fish 32: 249-265.
- Eccles, D.H. & Lewis, D.S.C.; 1981; Midwater spawing in Haplochromis chrysonotus (Boulenger) (Teleostei: Cichlidae) in Lake Malawi. Env. Biol. Fish. Vol. 6, No. 2, pp 201-202.
- Jensen J.; 1990; Plausibility and testability; Assessing the consequences of evolutionary innovations. pp. 171190 in M. Nitecki (ed), Evolutionary Innovations.
(This article was originally published in "The Cichlids Yearbook 3" Cichlid Press; pp. 92-93. It is here reproduced with the permission of author Martin Geerts).
- Konings, Ad. 1992. "Cyprichromis sp. "Leptosoma Jumbo"". The Cichlids Yearbooks. v. 2; pp. 26-27 (crc00805)
- Kuwamura, Tetsuo. 1988. "Biparental mouthbrooding and guarding in a tanganyikan cichlid Haplotaxodon microlepis". Japanese Journal of Ichthyology. v. 35(n. 1), pp. 62-68. DOI: 10.1007/BF02906685 (crc03726) (résumé)
- Kuwamura, Tetsuo & N. Mihigo. 1988. "Early ontogeny of a substrate-brooding cichlid, Boulengerochromis microlepis, compared with mouthbrooding species in Lake Tanganyika". Physiology and Ecology Japan. v. 25(n. 1), pp. 19-25 (crc03728) (résumé)
- Spreinat, Andreas. 1991. "Freilaichende Rhamphochromis". Die Aquarien- und Terrarien-Zeitschrift (DATZ). v. 44(n. 3), pp. 198-199 (crc05549)
© Copyright 1993 Martin Geerts, all rights reserved
Geerts, Martin. (mai 21, 1998). "Livebearing cichlids". Cichlid Room Companion. Consulté le février 25, 2021, de: https://cichlidae.com/article.php?id=93&lang=fr.