Identification
The bullhead is a small, stocky bottom-dwelling fish of 8 to 15 cm with a remarkably broad, flattened head that makes up nearly a third of the body. The body tapers toward the tail and is scaleless — the skin feels smooth and slimy. The color is brown to grey-brown with dark marbling that provides excellent camouflage on stones and gravel. The pectoral fins are large and fan-shaped, adapted to anchor the fish on the bottom in current. The species has two dorsal fins and a large, round mouth. Not to be confused with gobies, which have visibly scaled bodies.
Behavior & ecology
The bullhead is a territorial bottom fish that lives under stones, among riprap, and in crevices of hard bank protection. During the day it sits motionless in hiding; it only becomes active at dusk. It hunts small invertebrates: amphipods, midge larvae, and water lice. The species is strongly tied to hard substrate — stones, gravel, riprap — and is absent from soft, muddy bottoms. In spring, the male guards a nest cavity under a stone where the female has glued her eggs to the ceiling.
In the Netherlands
The bullhead is protected under the European Habitats Directive (Annex II). In the Netherlands, it occurs in the major rivers (Rhine, Meuse, IJssel), their side channels, and in canals and streams with hard substrate. The species benefits from riprap bank protection along rivers and canals — ironically, this human intervention provides excellent habitat. However, populations are under pressure from water pollution and competition with invasive gobies (round goby, tubenose goby) that occupy the same hiding spots. The bullhead has no significance for sport fishing.
What our models found for Bullhead
Below is what our models see in the data. These are links: where one thing occurs, the other occurs more often. That is not a cause. Each model answers one question and may not say more than it measured. The label by the heading tells you which question — and how sure the answer is.
Where this species lives Strong model
Three-spined stickleback (Gasterosteus aculeatus)This one IS the brook picture. The three-spined stickleback and the gudgeon come first, then the banded demoiselle (Calopterygidae) and freshwater shrimps (Gammaridae). Further down the chub, water mites of the family Sperchontidae, the stone loach, blackflies (Simuliidae) and caddisflies of the family Psychomyiidae.
Plants and shellfish of running water are in it too: horsetails (Equisetaceae) and pea mussels (Sphaeriidae).
Now the awkward part. We hold TWO bullhead columns in our data, and in Dutch both are called rivierdonderpad. The other column (Cottus gobio) is a feature in THIS model. So on the page the species appears to predict itself, and that is a fault in our naming, not in the fish.
The two models describe different water, by the way: this one is the brook, the other is big lowland water. According to FishBase the bullhead lives in both.
Where there are many Weak model
Water mites (Oxidae)This model is weak and one feature clears the floor: water mites of the family Oxidae. Where there are more of those mites, we count more bullhead. Beyond that this model says nothing.
