Bighead goby

Identification

The bighead goby (Kessler's goby) is the largest of the Ponto-Caspian gobies in the Netherlands, reaching up to 22 cm. The body is robust and stocky with a notably broad, flattened head. The color is dark brown to grey-brown with faint dark spots and bands. The pectoral fins are large and the body feels rough due to small scales. Characteristic is the heavy build — distinctly more massive than the round goby. Like all gobies, it has fused pelvic fins forming a sucker disc. The distinction from the round goby: the bighead goby is larger, more broadly built, and lacks the black spot on the first dorsal fin.

Behavior & ecology

The bighead goby is an aggressive bottom fish that lives on hard substrates in flowing water — riprap, quay walls, and gravel banks in large rivers. It feeds on invertebrates, snails, and small crustaceans, and its powerful jaws can crack mussels. The species is territorial and displaces other bottom fish from the best hiding spots. Originally from the lower reaches of rivers around the Black Sea and Caspian Sea, where it occupies the fastest-flowing sections.

In the Netherlands

The bighead goby is the fourth Ponto-Caspian goby species in the Netherlands and was first recorded in the major rivers around 2007. The species is most strongly tied to the main current of rivers — it prefers the strongest flow and hardest substrate of all invasive gobies. With 61% of observations in rivers, it is decidedly rheophilic. The impact on native bottom fish, particularly the protected bullhead, is considerable: the bighead goby is larger and more aggressive than the other invasive gobies and can directly displace the bullhead from its hiding spots.