News / Species Spotlight / What, pray tell, is a Pholidichthys (and what doth it eat)? (01/17/18)

What, pray tell, is a Pholidichthys (and what doth it eat)?

Species Spotlight - What, pray tell, is a Pholidichthys (and what doth it eat)?
All fishes are full of mystery, but some more than others and perhaps none so much as Pholidichthys, which aquarists will know as either the Engineer Goby or the Convict Blenny. But, in truth, it doesnt belong to either of these groups, and for generations this curious, eel-like genus has been a thorn in the side of ichthyologists hoping to unravel its evolutionary relationships. There really is nothing else quite like it, and the question of what it might be most closely related to has at times seemed almost unanswerable. Thankfully, recent studies have at long last cleared the air and revealed its true affinities, but much about this fish still remains to be discovered.

As it turns out, Pholidichthys is an almost-cichlid that is to say, genetic data supports it as the sister group to the hugely diverse and geographically widespread family of primarily freshwater fishes in the Cichlidae. Go figure

But aside from its enigmatic origins, there is a still greater mystery yet to be fully studied. Despite the abundance of juveniles in the wild (and in the aquarium trade), adults of this genus are only rarely seen, and little is known about how they survive. Mature specimens of Pholidichthys live reclusive lives in a self-constructed system of tunnels which can stretch for twenty feet or more. Its from here that vast swarms of juveniles emerge to scour the reef for plankton, returning each night to rest, hanging from the subterranean roofs of these underground passageways by a thin mucilaginous thread.

For such a large fish, able to reach over a foot in length, it might come as a surprise to learn that no one has ever seen the adults eat in the wild. Of course, they obviously must sustain themselves on something, but, alas, we know not what. Specimens have been collected for gut analysis, but, curiously, all that could be found was a thick, green goo of unknown origins. The most likely explanation is that the juveniles in some way feed their parents, which would be a wholly novel form of nutrition for reef fishes, but the specifics of how this works are entirely unknown. Also unknown is how Pholidichthys (which lives in mated pairs) breeds and raises its young, but, if theyre anything like their cichlid cousins, its quite probable that the eggs are either mouth-brooded or otherwise directly tended to by the parents.

Interestingly, mature specimens have no such qualms about feeding on traditional aquarium offerings, like flake food and frozen krill or mysis. How can a fish be so particular in its culinary preferences in the wild while simultaneously having such catholic tastes in the confines of an aquarium?! Yet another mystery.