Who’s weirder: the shark lady or the convict fish? It may seem a strange way to get this blog started again, but it turns out to be quite fitting this time of year when we find ourselves cooped up with relatives of all stripes.
My first encounter with the convict fish was this summer. It was one of those enigmatic creatures that blew all of the biologists in the room away, at one of our regular gatherings to watch the BBC’s Life series. Over images of thousands of tiny fish emerging from a burrow on the sea floor, David Attenborough explained the mystery. This was a swarm of siblings, all offspring of the same pair of adults who spend their entire lives in a tunnel. Each day, the young convict fish head out to forage on plankton around the reef, returning home at night. Biologists have no idea how the parents feed, though, because no one has ever seen the adults leave their burrows in the wild. Attenborough left us hanging, suggesting with intrigue that the young fish might have something to do with it.
Could the convict fish be living off of its own offspring? A bit grim, yes, but also a fascinating biological paradox – perfect for this blog on the stranger twists of evolution, I thought. In nature, it might not even be that unusual. The males of plenty of fish species feed on eggs from their own nests. By taking in extra resources, this might allow them to invest more in future nesting attempts1. In fish with especially large broods, once filial cannibalism gets started it could get an evolutionary boost from the fact that many of the offspring in dense egg masses will not survive anyway2.