If the symptoms are alleviated by a partial water change (you didn't mention what your regular maintenance schedule is), I suspect the problem is probably environmental.
Q. I have a 55-gallon Lake Malawi cichlid aquarium with several Synodontis catfish, among them a Synodontis angelicus and a Synodontis multipunctatus. I am having trouble finding information on these beautiful fish, but in particular I have heard of a "cuckoo" reproductive relationship between Synodontis and mouthbrooding cichlid fish. I am very interested in these catfish, so I would appreciate any information on breeding Synodontis in captivity.
Also, occasionally these catfish develop extremely bloated bellies, similar to "Malawi bloat." The symptoms go away shortly after a partial water change. There have been no catfish deaths as a result of it (I have not had a Synodontis die in four years of fishkeeping!). Do you have any idea as to the nature of this illness?
A. Congratulations on successful Synodontis keeping! Although I've never seen the bloating problem you describe, it sounds as if you've solved it yourself. If the symptoms are alleviated by a partial water change (you didn't mention what your regular maintenance schedule is), I suspect the problem is probably environmental.
Happily, although not yet a regular aquarium event, hobbyist spawnings of Synodontis multipunctatus are increasing in frequency each year. I believe a previous Aquarium Fish International columnist Lee Finley was the first to use the term "cuckoo" relationship between maternal mouthbrooding cichlid fish and Synodontis multipunctatus. Lee was referring to birds that lay their eggs in the nests of other species. The nesting parents incubate the "foreign" egg, which hatches a nestling large enough to push the other baby birds out of the nest to their death. The parents continue to feed the nestling as if it were their own offspring until it fledges and leaves the nest.
In terms of Synodontis catfish, baby multis have been found in the mouths of "holding" cichlid fish females. That is, they were picked up (as eggs) and orally incubated along with the spawning female's own eggs. The possible trigger for the spawning of the multipunctatus parents may be the spawning of the cichlid fish. It is likely to be a chemical trigger — pheremones — rather then a visual trigger. The multipunctatus fry hatch much sooner than the cichlid fish fry, and the catfish fry's first food appears to be the African zygotes in the parent's mouth.
I'd like to note that Ron Soucy of S & S Aquariums in California has been successfully breeding multipunctatus without the presence of African cichlid fish. As the multis scatter their very small eggs, he scoops them up with a brine shrimp net and hatches them in a tumbler (as would be done with African cichlid fish eggs that had been stripped from a holding female). His observations and success seem to contradict everything that we think we know about these spawnings.