Catfish of Lake Malawi

By Jim Greenwald

When Lake Malawi comes up in a discussion, cichlids are immediately thought of. Granted, the Mbuna cichlids of Lake Malawi are colorful and interesting, but the lake contains other creatures as well.

Catfish from Lake Malawi are rare in the hobby, probably because there is little interest in them and they get little publicity. They are hard to catch and even harder to ship. Most catfish are nocturnal and no native diver really wants to go out looking for catfish at night when he could be safe at home, making plenty of money from cichlids.

So what do we have in the way of catfish from Lake Malawi?

In Lake Malawi, cichlid juveniles have been seen clustering around the nest of catfish Bagrus meridionalis. the The young cichlids were reasonably safe, only being threatened by the mother catfish when they came too close to her own fry. The catfish young benefit from this behavior because a predator attacking the nest would most likely go for a cichlid juvenile. The juvenile cichlids benefit from the mother catfish defending her nest against a predator and defending them as well.

Well, interestingly enough, the largest fish native to Lake Malawi, is this same giant predatory catfish that can weigh in at several hundred pounds. Bagrus meridionalis catfish and cichlid parents engage in a mutualistic defense of their young from predators. Over 50% of this catfish’s broods observed in Lake Malawi contained cichlid young, primarily of three species: Copadichromis pleurostigmoides, Ctenopharynx pictus and a Rhamphochromis species. Three different catfish broods, monitored over a period of 50 days, had a survivorship rate six times greater during periods when cichlid young were present than when cichlid young were not present. During two and one half hours of observing catfish broods without cichlids, 23 strikes by predators were observed on the catfish young. However, when cichlid young were present no foraging attacks were observed upon the catfish, but 32 occurred against cichlid young in the same two and half hours of observation. When the catfish parents were experimentally removed the cichlid young were consumed first then the catfish young followed, plainly indicating that cichlid young taste better. When cichlid young were present the catfish young survived over 80% longer than those in broods without cichlid young. It can only be concluded that the parental catfish increase the survival of their own young by allowing cichlids into the brood. Because of a difference of costs between the two species, cichlid mothers are more likely to abandon these interspecific broods than are the catfish.

There is only one described Synodontis in Lake Malawi, Synodontis njassae. In addition one another Synodontis which is so far undescribed has been found in the lake. Based on that fact, I would conclude that Synodontis has found the lake non friendly to species diversification so far. Synodontis njassae shows a widespread distribution in Lake Malawi. Fryer, in the CICHLID FISHES OF THE GREAT LAKES OF AFRICA, reported it to be only found in sandy areas but other reports indicate that it may also be found in the rocky areas that are common throughout the lake. It is commonly found in shallow water but sometimes may also be found in very deep (75 meters) oxygen poor waters.

There appear to be a large variety of spot patterns identified with this fish. The spotting pattern is not consistent between fishes and while some have numerous spots, many conversely have few spots. The difference between the njassae and the undescribed species appears to be the depth of the body.

The Clariidae family of catfish are represented by the Genus Dinotopterus. These are large growing fish, a lot like the Clarias catfish we are familiar with and are piscivores, making them unsuitable for the home aquarium. They are elongate and tend to just sit on the bottom and wait for their lunch to appear. At night, they cruise through the rock crevices looking for sleeping, tasty morsels. This genus is found through-out the lake.

The cichlid Pseudotropheus crabro has developed an interesting feeding niche. Crabro has a symbiotic cleaner fish relationship with the larger catfish and therefore is normally found in the large caves in which the Catfish lurks during the day. So far has this little cichlid carried this behavior that it will sometimes follow a diver in a black wet suit over long distances, presumably looking for more parasites.

Since the Bagrus meridionalis grows over 300 pounds, a diver could easy appear as a medium sized catfish to a small Mbuna.

Pseudotropheus crabro picks the parasitic Argulus africanus (a fish louse) from the catfishes skin. The parasites are so firmly attached that they are only removed by the scraping action of Pseudotropheus crabro.

One cichlid, Docimodus evelynae also uses catfish as a food source.This cichlid feeds on catfish by picking off pieces of their bodies. Both Bagrus and Clariidae pieces have been found in their stomachs.

So as you can see catfish play an everyday part in the cichlid lives in Lake Malawi.

References:

Boulenger, G.A. 1897a. Descriptions of new fishes from the upper Shiré River, British Central Africa, collected by Dr. Percy Rendall, and presented to the British Museum by Sir Harry H. Johnston, K.C.B. Proceedings of the Zoological Society of London 1896 (part 4): 915-920 & Plate 47. [Corematodus, Docimodus]

Burgess, W.E. 1976c. Studies on the family Cichlidae: 6. A new shell-dwelling cichlid from Lake Malawi and its inquiline catfish. Tropical Fish Hobbyist 25 (1): 39-48. [Pseudotropheus lanisticola]

Eccles, D.H., and D.S.C. Lewis. 1976. A revision of the genus Docimodus Boulenger (Pisces: Cichlidae), a group of fishes with unusual feeding habits from Lake Malawi. Zoological Journal of the Linnean Society 58 (2): 165-172.

Fryer, G., and T.D. Iles. 1972. The cichlid fishes of the Great Lakes of Africa. Oliver & Boyd, Edinburgh; TFH Publications, Neptune City, New Jersey; 641 pp.

Jackson, P.B.N. 1961. Check-list of the fishes of Nyasaland. Occasional Papers of the National Museums of Southern Rhodesia 3 (25B): 535-621.

McKaye, K.R., and M.K. Oliver. 1980. Geometry of a selfish school: Defence of cichlid young by bagrid catfish in Lake Malawi, Africa. Animal Behaviour 28 (4): 1287 & Plate 1.

Ribbink, A.J. 1991. Distribution and ecology of the cichlids of the African Great Lakes. Pp. 36-59 in Keenleyside, M.H.A. (ed.), Cichlid fishes. Behaviour, ecology and evolution. Chapman & Hall, London.

Ribbink, A.J. and D.S.C. Lewis. 1982. Melanochromis crabro sp. nov.: a cichlid fish from Lake Malawi which feeds on ectoparasites and catfish eggs. Netherlands Journal of Zoology 32 (1): 72-87.


Last updated 31 May 2004, 1400, BL