Bullheads are very well camouflaged, scaleless and brown/grey in colour with mottling that can change according to the surrounding substrate, with a pale belly. The male turn black with a white-tipped dorsal fin in the breeding season when the females become very obviously gravid with roe.
These fish are quite stubby, having a large head in proportion to their body with a wide mouth, large pectoral fins and prominent eyes set high up on a wide flattened head, perfect for a predatory life on the bottom of clear streams and rivers.
Adults are territorial and are quite sedentary and possess no swim bladder, meaning that they naturally sink in the water, likely to be linked to their relative lack of movement with studies having revealed that some will only move 4-10m over a period of 8-months with a home range being based upon a single stone with stones of 0.25m in height providing a barrier that they do not cross!
Bullhead’s are widely distributed in England, generally in well oxygenated streams, rivers and sometimes lakes with hard stony substrates. They prefer shallow, fast-flowing streams and are an indicator of water quality, found in the riffles of these rather than the pools. Colonisation upstream of new environments will only occur slowly as the adults move very little, having a range of 10m, whilst their newly hatched larvae will be easily swept downstream.
Bullheads spend daylight hours hiding under stones and in vegetation, coming out at dawn and dusk to feed on small crustacea, invertebrates (especially insect larvae), fish eggs and small fry: even their own young!
Bullheads spawn in February to June in water temperatures between 8 to 16°C. Males court several females, that can lay between 100 to 400 large pale yellow eggs about 2mm in diameter. The eggs are pale yellow and are laid in ‘nests’ beneath stones or in a pit, with the male then guarding them against predators, including caddis fly larvae, whilst fanning the eggs with his pectoral fins to ensure a good supply of oxygen. The larvae hatch at 6-7mm long after 20-30 days dependant on temperature, absorbing their yolk sac within 10-days.
These are not generally a rod and line target, but try very small hooks cast into shallow water where careful observations may reveal them in the shallows.
Check out the galleries for both fisheries and the Wildlife gallery where a Bullhead that lives under the logs at the front of The Oaks swim at Frensham Great Pond was photographed. I would also expect the River Loddon would have them as well.
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Since Bullheads occupy such small areas of their host stream or river, it is believed that British Bullheads may be genetically different to those found in Europe. Indeed, even different river systems within the UK may have genetically different fish and it is even possible that genetically different populations may occur within the same river as they may not inter-breed.
Bullheads spawn in February to June, with males courting and mating with several females, that can lay 100 to 400 large pale yellow eggs about 2mm in diameter. The eggs are pale yellow and are laid in ‘nests’ beneath stones or in a pit, with the male then guarding them against predatory caddis fly larvae and fanning the eggs with his pectoral fins to ensure a good supply of oxygen, the larvae hatch at 6-7mm long after 20-30 days dependant on temperature, absorbing their yolk sac within 10-days.
The fry grow quickly attaining 40-50mm in the first year and 70-90mm when 3-years of age and sexually mature, typically living for just 3 – 4 years, they have been recorded as living up to 10 years. Bullheads are generally very small and with the British record being 5oz (141gr).
Bullheads fall prey to many species of fish including Eel, Chub, Brown Trout, Perch & Pike as well as piscivorous birds, such as Grey Herons, Kingfisher and Dippers all feeding on them.
The nickname Millers Thumb is thought to originate from times when millers of flour sold people short, by using their thumbs to lift the weights on old weigh scales when selling flour to give a false reading, thus improving their profits !
Another possibility is that their flattened heads or very large pelvic fins (in comparison to body size), may have resembled those millers unfortunate enough to catch their thumbs in the grinding stones of the water mills that were located adjacent to the streams and rivers, harnessing the rivers flow to turn the water wheels and subsequently turn the milling equipment for many different milling jobs, since their introduction from the 12th Century in Britain.