TROPICAL Synodontis
A Synodontis DEEP DIVE
While not as popular as plecos or Corydoras, the Synodontis of Africa are enthralling fish with their own evolutionary party tricks. Neale Monks explains.
SHUTTERSTOCK
Synodontis have an almost ‘sharky’ appearance.
NEALE MONKS
Neale is a longstanding aquatics author with a particular passion for brackish water species.
PIEDNOIR AQUAPRESS.COM
SYNODONTIS ARE by far the most regularly traded African catfish. Something like 120 species have been described, of which a good dozen or so can be found in aquarium shops. The dwarf upside-down catfish, Synodontis nigriventris, is commonly traded and a fine addition to most community tanks. Others, like the famous polka-dot catfish, Synodontis angelicus, are bigger but not particularly difficult to keep, and with care can be kept with medium-sized tankmates without problems.
In fact, Synodontis are an impressively widespread group of fish with different species found across much of sub-Saharan Africa including the Congo River system and the Rift Valley lakes. Indeed, Lake Tanganyika in particular has a ‘species flock’ of closely related species that have likely evolved within the lake, each adapting to a particular niche. While the flock is quite small — around ten species — they are quite diverse, including at least two species that are brood parasites (of which more later).
Evolutionary niches
If that’s reminding you of an even bigger fish family, the Cichlidae, you’re not wrong. Professor Julia Day at University College, London, and her colleagues have been studying this Lake Tanganyika species flock and learned some interesting things about them.
One is that these Synodontis species evolved quite recently, within the last 8 million years, following the colonisation of the lake by a single ancestral Synodontis species.
More surprising perhaps is that unlike Tanganyika, neither Lake Malawi nor Lake Victoria has Synodontis species flocks. Instead, each has just the one endemic species. Day observes that “…it is notable that although all three great lakes have sizeable cichlid radiations, Tanganyika’s comprises ‘fewer’ species, with less than half that estimated for Lakes Malawi and Victoria.” She suggests that the relatively lower cichlid diversity in Lake Tanganyika may have left some ecological niches for Synodontis to fill, whereas the larger and more diverse cichlid communities in the other two lakes occupied more of those ecological niches, putting a lid on the potential for Synodontis diversification. She also suggests that it’s also possible the age of Lake Tanganyika is a factor, the other two lakes being younger, which means there’s been less time for new species to evolve.