The scale of the radiation is the point. Estimates of Malawi cichlid species run from around 500 to nearly 1,000, with most still undescribed, and something close to all of them are endemic to the lake. They occupy sharply divided roles: rock-dwelling mbuna that scrape algae, sand-sifters, snail crushers, open-water hunters and specialists that eat scales or fins.
Genomic work published in 2018 on more than a hundred Malawi species indicated a single radiation from a small ancestral population, with lineage divergence young enough that many species remain able to hybridise. Depth, substrate and light environment segregate them physically, while divergent male colouration and female preference maintain separation without geographic isolation.
That last mechanism is fragile. Where water becomes turbid, the colour signals females use to choose mates are degraded, and species boundaries can collapse through hybridisation. This has been documented most clearly in Lake Victoria; how far the same risk applies across Malawi under increasing sediment loads is not yet clear.