Dwelling on the bed of our swift-flowing rivers is one of our commonest and distinctive fish species, the Bullhead. While it’s certainly a diminutive fish, it has a relatively large chunky head that does give it a certain bullishness. Another common name for it is Miller’s Thumb, probably because they are digit-sized and typically inhabit the kind of energetic rivers that were for centuries strung with watermills.
I think Bullheads must be really common in Sheffield’s rivers. Many a time we’ve inadvertently caught one when using pond-dipping nets to collect invertebrates from the river bottom. They squirm weakly in our dank catch of insect larvae, crustaceans and grit, and look accusingly at us with upward facing eyes. If it’s so easy to catch one from a small patch of riverbed then surely they must be down there in their thousands?
Apparently Bullhead are good dads. Female fish visit males and deposit around 100 eggs which the soon-to-be fathers protect and care for until the resulting fry are free-swimming, a level of parental care found in only a handful of British’s freshwater fishes. Neither sex is very sociable, preferring a solitary existence, and establishing small territories that they defend and occupy for their entire lives; tiny underwater fiefdoms of cobble and stone.
In the mornings and evenings Bullhead become more active to feed. They are omnivorous and eat a wide range of food including freshwater shrimp, midge larvae, fish fry, as well as plant matter. They wisely stay hidden away in the daytime, sheltering in gaps under rocks, to try avoid their many predators such as grey heron, kingfisher, otter and brown trout. I think it’s a sensible approach to being a small fish in a big river.
Bullhead need well oxygenated cleanish water and for a long time they were absent from Sheffield’s grossly polluted rivers. That they are now thriving in the River Don in Sheffield demonstrates how much water quality has improved. They are hard to spot, but if you look into the Don and see a boulder or cobble, or maybe even a brick, there’s a good chance there’s one of these charming fish secreted underneath, waiting out the day until it can safely emerge for its supper.