Pigmentation of young fish as a clue to relationships between the species of Bushfish

by Michael Kokoscha, IGL

In 1866, Ernst Haeckel formulated the ground rule whereby the development (ontogenesis) of an organism represented a shortened recapitulation of its evolution (phylogenesis). From the development of the individual (particularly the embryo) the evolution of a whole group can be deduced. A well-known example of this is the development of gills, which are found during the development of all embryos, including humans.

If you want to use this rule to assist in classification of the species, you have to be careful because you must differentiate between structures which repeat the phylogenesis (eg the seam around the fins) and those which are part of its own development (eg the adhesive gland of the anabantoids, sub family. Macropodinae). Adaptations of the second kind could give valuable assistance with taxonomy but they have to be regarded with caution because they could have evolved for a particular purpose, independently.

A certain pigmentation in young fish could also be a new adaptation (eg as camouflage) but it could also be a recapitulation of a common ancestor. This, it seems, is really the case with bushfish(Ctenopoma) as, even today there are species which look like an assumed ancestor. The pigmentation in young fish could, in this case, be a way of differentiating groups within the rather large genus, Ctenopoma.

An important division was already recognised by Peters (1976) because of the 'thorn fields' which occur in the males.

  1. Species with 'thorn fields' behind the eye and on the stem of the tail: C.acutirostre, C.kingsleyae, C.macultum, C.muriei, C.ocellatum, C.oxyrhynchum.
  2. Species with 'thorn fields' behind the eye only: C.multispinnis, C.nigropannosum, C.pellegrini.
  3. Species without 'thorn fields' : C.ansorgei, C. damasi, C.fasciolatum, C.nanum.

The relatives within the third group, in contrast to the other two, look after their brood and build bubblenests. The differences are also shown in the pigmentation of young fish. After hatching, the young seem finely spotted (photos of C.ansorgei in Leser, 1979 and of C.fasciolatum by Lubeck and Wetzel 1988 and by Morike in 1977 of C.damasi. (I have seen the same thing in C.nanum.)

I observed in C.fasciolatum and in C.nanum, after the spotted phase, the front of the body becomes dark while the rear remains light. In the third phase, the body is grey-brown and there is a spot on the root of the tail. This disappears again, when the fish gets its permanent colour. These different stages in pigmentation are probably common to all bubblenest builders.

In the relations from the 1st group (2 'thorn fields'), the spotted stage appears at best, just before or just after hatching (with the exception of C.muriei). This group can be further divided into 2 sub-groups:-

  1. C.oxyrhynchum and possibly the similar, C.maculatum.

    Here the pigmentation does not only apply to the front of the body but the root of the tail also has dark pigmentation. During the development of the fish, the 2 sections move closer to each other so that there is a light band in the middle of the body, in the middle of which sits the eyespot on the fish's flank. A light line runs from the mouth, through the eye to the origin of the caudal and forms, if seen from above, an oval. As the fish can change colour with their moods, you can occasionally see these colourings in adult fish of both species.

  2. C.kingsleyae, C.ocellatum and probably also C.acutirostre.

    Here the first half of the body, the middle of the body, (the tails stem in the larvae) and the root of the tail, have dark pigmentation (photos Ostermueller, 1971). The dark areas converge, so that there appears to be a vertical light line in the middle of the body, as well as the already mentioned line through the eye, as in C.oxyrhynchum. This is particularly obvious in C.kingslyaeand is exactly as described for C.argentoventer by Arnold and Ahl in 1936. It is possible thatC.argentoventer is a very close relation of the original form.

    After the disappearance of these markings, the young C.kingsleyae show markings which look like the third phase of the bubblenest builders or the adult pigmentation of C.muriei. The spot on the tail does not result from the original tail root pigmentation. Later on, C.kingsleyae become darker and get their slate grey adult colour. In C.ocellatum (and surely also C.acutirostre) the dark areas decay by attaining the 'argentoventer stage' in spots, so the line markings are not noticeable anymore (Photos Kokoscha, 1989). These markings, which are similar to those of the adult C.acutirostre are still to be seen on my brood of C.ocellatum which are now over a year old. If there is no change in colouration one will have to regard C.ocellatum as a colour variant ofC.acutirostre (but see Labyrinth 48 for a discussion of skeletal differences between these spp- Ed.).

    In the group with 2 'thorn fields', C.muriei occupies a special place. Whilst it definitely belongs to this group, because of the 'thorn fields', the young fish show for at least a week, the spotted markings of young bubblenest builders (Morike 1977). The further development of the pigmentation is unfortunately not absolutely clear. I think therefore that it might be possible thatC.muriei is related to an original form from which evolved both the bubblenest builders, which had a special way of raising their brood and also the other specialised species (leaf fish) which both have 2 'thorn fields'. If this ancestor already had the 'thorn fields' is uncertain at this time. It is possible that these fields might recede when they are not needed (outside the breeding season).

    We might learn more if we compared this group with the group with 1 'thorn field'. Unfortunately, little is known about this group. It is possible that 2 very different groups have been thrown together. Whilst the eggs of C.multispinnis are lighter than water (Benl and Foersch, 1978), the eggs of C.pellegrini sink to the bottom (Seegers, 1988). (However, mine didn't- they floated -Ed.)C.nigropannosum should be closer to C.pellegrini.

    We should also consider Sandelia, the south African labyrinth fish. Here we have an observation from nature which says that the eggs sink and are guarded by the male (Harrison, 1952). Before we start a revision of the family to which Ctenopoma and Sandelia belong, it would certainly be useful to examine the development of the young fish for which no information currently exists. It would be unwise and hasty to separate the bubble nesters from the free spawners as is sometimes suggested.

  3. References

    Arnold, J.P. and Ahl, E. 1936. Fremdlandische susswasserfische. Braunschweig.
    Benl, W. and Foersch, W. 1978. beitrag zur Kenntnis des Ctenopoma multispinnis Peters 1844. Spixiana 1, 3 287-299
    Harrison, A.C. 1952. The cape Kurper. Piscator 23, 82-91.
    Kokoscha, M. 1989. Zwei afrikanischje labyrinthfische: Ctenopoma acutirostre und Ctenopoma ocellatum DATZ 3/89 also in English A&P Nov '89 52-3.
    Lubeck, K and Weitzel, M. 1988. Zur zucht des Gebanderten buschfisches. DATZ 531-533.
    Moricke, D. 1977. Vergliechende Untersuchen zur Ethologie zweier Labyrinthfischarten, Ctenopoma muriei (Boulenger, 1906) und Ctenopoma damasi (Poll 1939), (Anabantoidea, Pisces). Dissertation, Tuebingen Univ.
    Ostermoller, W. 1971. Der Schwanzfleckbuschfisch (Ctenopoma kingsleyae) - seine Pflege und Zucht. DATZ 14-16, 44-47.
    Peters, H.M. 1976. Geschlechtmerkmele bei Afrikanischen Buschfisch. Aquarien Mag. 292-296.
    Seegers, L. 1988. Was ist Ctenopoma ashbysmithi? DATZ 291-295.

    Reproduced from 'Der Makropode' with permission and translated by Mrs R. Armitage (Wyneken)

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