Article © Julian Dignall, uploaded July 01, 2002.
The Rift Lakes of East Africa, comprised primarily of Lakes Tanganyika, Malawi and Victoria, are famous for the enormous diversity of the fishes that inhabit them. The amazing tale of cichlid speciation in these magical lakes has often been told. But while cichlid specialists have studied these lakes exhaustively, relatively little attention has been paid to catfish from the Rift Lakes. While the number of catfish species in the Lakes is much smaller than that of cichlid species, recent imports reveal that it is greater than we had previously known.
Of all the Rift Lakes, the greatest Siluriform diversity is to be found in Lake Tanganyika. It is by far the oldest of the Rift Lakes, with an age of approximately 6 million years, and also the deepest, with a depth of some 1,500 meters (though 99% of the fish life is concentrated in the topmost 200 meters). Species from the families Clariidae, Claroteidae, Malapteruridae and Mochokidae are all relative pillars of the Lake Tanganyika community, but it is the local Mochokidae, and specifically, the local Synodontis, that is both most numerous and of the greatest interest to the aquarist.
Seven species have been described by science: S. multipunctatus Boulenger 1898, S. granulosus Boulenger 1900, S. nigromaculatus Boulenger 1905, S. dhonti Boulenger 1917, S. tanganaicae Borodin 1936 (known as S. lacustricolus until this name was declared a junior synonym of S. tanganaicae by De Vos & van den Audenarde in 1998), S. petricola Matthes 1959, and S. polli Gosse 1982 (formerly known as S. eurystomus). All except S. nigromaculatus are endemic to Lake Tanganyika (i.e. they are found nowhere else). With the passage of time and as a result of more intensive collection and export of aquarium fish from the lake, it is becoming clear that many more undescribed endemic species exist. If we were assigning "M numbers" for hard-to-identify Mochokids, we'd be giving Corydoras' C-numbers and Loricariid L-numbers a run for their money!
Figure 1: Close-Up of Head
S. multipunctatus, the subject of this Catfish of the Month, is by far the best known and the most readily available of the seven identified Lake Tanganyika Synodontis species. All the endemic species share the same basic coloration of black spots on a copper or brown background, with white barbels and white fin edging (though S. granulosus and S. dhonti both lose their spots as they mature). This makes them notoriously difficult to identify correctly, and identifications by vendors and hobbyist publications are often wrong.
Figure 2: Humeral Process
Relative to the others, however, S. multipunctatus is relatively easy to identify. It has big eyes (see Figure 1), which are larger than those of any other Lake Tanganyika Synodontis, and an unspotted white belly, unique among the seven described species. The humeral process has a distinctive dagger shape (see Figure 2, where it is outlined in black).
Most S. multipunctatus seen in the hobby conform to the same basic pattern, but variant types can sometimes be found. Figure 3 shows a fish from Zambia which appears to be a S. multipunctatus but has smaller eyes, an off-white rather than copper background coloration, a sharper humeral process (shaped like a reclining "Y" rather than a reclining "V") and exhibits bolder, more restless behavior.
Also called the "Cuckoo Catfish", S. multipunctatus is the only fish known to practice brood parasitism. Like the cuckoo, it lays its eggs among those of another species - mouth-brooding cichlids, in the case of multipunctatus - tricking the parents of the other species into raising its young. To add injury to insult, the catfish fry often end up eating their cichlid brood mates!
Figure 3: S. multipunctatus (Zambia)
This torrid tale of lust and deceit begins when the S. multipunctatus sense, through a combination of pheromone and visual cues, that a mouth-brooding cichlid species is in the midst of its mating and spawning rituals. Male and female catfish swoop down on the cichlid pair in flagrante delicto, gobbling up the cichlid eggs while scattering and fertilizing their own. In a few seconds the marauders are gone, usually chased away by the irate paternal cichlid. The maternal cichlid proceeds to hastily pick up the eggs, including the catfish's, which she then incubates in her mouth. The multipunctatus eggs typically hatch in just three days, several days before the cichlid eggs do. The fry begin to feast first on the cichlid eggs, and once those hatch, on the cichlid fry. When the mother finally releases "her" young, out swim a little swarm of well-fed baby Synodontis! The mother cichlid is so oblivious to the fact she has been duped that when alarmed, she will even take the Synodontis fry back into her mouth!
In the wild, S. multipunctatus parasitizes species such as Tropheus moori, Ctenochromis horei, Simochromis diagramma, S. babaulti and Pseudosimochromis curviforns. Interestingly, over the evolutionary eons, these cichlid species native to Lake Tanganyika appear to have developed a genetic memory of being cuckolded by S. multipunctatus, and are not easily duped. In the avian world, brood parasitism is a fairly common strategy, with about 1% of bird species laying their eggs in other species' nests. Rejection of alien eggs is also common, reflecting the evolutionary incentive to minimize the negative impact of brood parasitism on the host's reproductive success. It is thus not surprising that Tanganyikan cichlid species which have been parasitized by S. multipunctatus for thousands of years should also have "learned" to avoid losing their young in this way. We know of no reports of aquarists successfully spawning S. multipunctatus with a Tanganyikan cichlid host. Cichlids from Lakes Malawi and Victoria, on the other hand, do not appear to have thisgenetic wariness, and have proven much easier to work with in spawning S. multipunctatus in the aquarium. Victorian Haplochromines are best suited to this purpose.
Figure 4: Ten-week old fry
While S. multipunctatus seems to prefer to spawn with a cichlid host, it can also spawn without one. The eggs are perfectly capable of hatching and the fry of developing normally without cichlid (or human!) intervention. This has been well documented by several aquarists, and we have seen it ourselves. Spawning without a cichlid host has not been documented in the wild, but we expect that it must occur. Some scattered eggs probably fall into cracks and crevices where they are overlooked by the maternal cichlid and remain out of harm's way. More fundamental reasons why exclusive reliance on a strategy of brood parasitism is unlikely, include:
- the large population of S. multipunctatus in Lake Tanganyika,
- the fact that larger females can hold up to a hundred eggs at a time, but only a small number of these is released in each sortie on a mating cichlid pair,
- the evident familiarity of Lake Tanganyika mouth-brooding cichlids with S. multipunctatus' wily ways, and
- the fact that surveys in the lake have found relatively few cichlids carrying catfish eggs and fry.
The fry grow quickly, have a healthy appetite and can fend for themselves from an early age. At a week old, they have black bands on a cream background, but by about eight weeks the bands break up into the spots characteristic of adults (see Figure 4). Leaving the fry with their parents is a viable option if the tank is uncrowded and has lots of little nooks and crannies in which they can hide, but if the fry can be removed to a separate tank, they will grow out more quickly and be safe from predation. Live baby brine shrimp are the favored food till the fry are about a month old, followed by chopped up live bloodworms from one to about three months, and whole bloodworms thereafter. The fry don't much care for flake foods, but will accept crushed Tetra ColorBits, which can be used to supplement live foods. As with all heavily fed fry, frequent water changes and waste removal are a must.
All Synodontis are long-lived fishes with a distinct life-cycle, and this is also true of S. multipunctatus. From about six months to about 3-5 years of age, S. multipunctatus is in its adolescent stage. Towards the end of this period, growth plateaus and the fish become sexually mature. Thereafter, they have another five years or so of vigorous adulthood ahead of them till they start to show signs of age. While senior fish may not long survive the rigors of the wild, this is not necessarily true in a sheltered aquarium environment, where S. multipunctatus may well live to an age of 15 or more years.
We know a lot about S. multipunctatus, but there is still much more to learn. And that may be the most wonderful thing of all about this little cuckoo among fish: it is accessible, but has not yet revealed all its many mysteries!
Copyright information for the images used in this article can be found on the species' full Cat-eLog page.
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