We don’t tend to celebrate fish unless they’re edible or big and spectacular. The bullhead (AKA miller’s thumb or tommy logge) is, at first glance, the very antithesis of this. It’s a small and unobtrusive fish of streams, rivers and lakes, not much bigger than a human digit when adult. Yet, however diminutive it may be, the bullhead is full of surprises.
What is the bullhead fish and what does it look like?
First up, it is a member of the sculpin family, most of which are actually marine fish. Look at a long-spined sea scorpion – a common rockpool fish – and you’ll immediately see the family resemblance. There is the knobbly head taking up more than 25 per cent of the fish’s 7–9cm length; bulging eyes mounted high up and a pair of big, flounced, wing-like pectoral fins.
Where do bullhead fish live?
In common with its cousins, the bullhead doesn’t have a swimbladder. Therefore, it is a ‘benthic’ beast – that is, it lives at the bottom of a body of water. The species is superbly cryptic, too. A mottled palette of browns and blacks helps it to blend in amid pebbles and rocks.
Despite being small in size, the bullhead makes up for it in ecological impact, being an incredibly important food fish. Its many predators include trout, salmon, kingfishers, herons and otters (even, historically, humans).
How do bullhead fish mate and reproduce?
From spring to mid-summer love is in the water. A frisky male bullhead setting up his territory becomes much darker and his first dorsal fin develops creamy white edging. He is now in full battle dress – a livery to match his mood – and aggressively
defends his little patch of stream or riverbed. The fulcrum of all this activity is almost always a rock large enough to be his fortress.
I still vividly recall the child’s thrill of gently lifting fist-sized stones in a stream, then waiting with bated breath as the swirl of displaced silt and sediment settled down, to see if the clearing water revealed a bullhead glaring back at me with indignation. If I was even luckier, the underside of his rock would be plastered with treasure: a mass of up to 400 yellowish-white eggs, which meant he’d managed to woo a female. How the male bullhead goes about this is yet another wonderful surprise.
To entice a female to his love lair, the male ‘sings’ – maybe not quite as tunefully as that word suggests, but impressive, nonetheless. By rubbing the bones of his pectoral girdle against those of his skull, the fish delivers effective pulses of sound in the 50–500Hz range – anywhere between four and six of them. He can even hit notes up to 3kHz.
This dull thudding sound seems to penetrate the higher frequency background noise of a stream or river’s acoustic landscape. It has the effect of luring a female, who we can only assume recognises qualities in our male that she alone can perceive. Female bullheads will also sing, but to a lesser extent.
If the pairing is successful, the female lays eggs under the male’s stone. After fertilisation, he’ll sit by and guard the eggs against predation. Patiently he fans the clutch, keeping it clear of sediment and ensuring a plentiful supply of oxygen
