Order: Scorpaeniformes Family: Cottidae
Foto: Lauri Urho
Description: The fourhorn sculpin has a dark, flecked body, large pelvic fins, a big head and large mouth. The sea-dwelling form is distinguished by four rounded rough knobs on the head, which are absent from the landlocked, freshwater form. There are several straight spines on the head and, compared with other freshwater bullheads, the caudal peduncle is long, about as long as the caudal fin itself. Signs of adaptation to bottom life are the location of the eyes almost on top of the head, the slightly flattened body, and the absence of a swim bladder.
Origin and distribution: The fourhorn sculpin occurs in northern North America, Greenland and northern Eurasia. In Europe, it is found in the sea only east of the North Cape and in the northern Baltic Sea. In Finland, it also occurs in the three main watersheds, in several deep lakes. At the final stage of the latest glaciation there was a large glacial lake in the Onega river basin draining into the White Sea. It is possible that the fourhorn sculpin migrated into this lake from the Arctic Ocean, and later from there into the Baltic Sea basin. The fourhorn sculpin lived in fresh water for some thousand years and, as a consequence, the form of the species that inhabits the Baltic Sea has lost its ability to tolerate a normal oceanic environment; it survives, however, in brackish water. In Central Finland, the landlocked fourhorn sculpin occurs in about 30 lakes, all of them north of the Salpausselkä water divide.
Reproduction: Fourhorn sculpin spawn in winter. In Finnish coastal waters they reach sexual maturity at 2─3 years of age and a length of 15─17 cm. The male digs a spawning pit on the bottom at a depth of about 10─20 m, into which the eggs are released as one lump. The incubation period lasts slightly over 3 months, and during that time the male fans and guards the eggs. Eggs are usually greenish, but other shades from maroon to orange also occur.
Diet, growth and migrations: Fourhorn sculpin grow larger in brackish than in fresh water. In inland waters, they are usually 10─15 cm long, but in the sea they grow up to 20─30 cm. Growth is fast in the first year, but slows down after that. The biggest individuals caught in the sea have weighed about 1 kg. Fourhorn sculpin feed on bottom fauna and fish. In deep brackish waters their main food is aquatic sowbug (Saduria entomon). Other important prey are mysids and shrimps. As they grow, and also when they migrate into shallow waters in the autumn, they switch increasingly to prey on fish. Particularly in winter, their stomachs contain the eggs of other fish species. The fourhorn sculpin suffers from the reputation of being an egg predator, but the eggs eaten usually originates from its own species. In lakes, small fourhorn sculpin feed mainly on crustaceans. In the sea area, the larger fish migrate from shallow to deeper waters in the spring or early summer, returning to shallow water in the autumn. The main reason for this migration is thought to be an attempt to avoid warm water, as fourhorn sculpin have poor tolerance of water over +10 °C.
Fishing and catches: In earlier times, the fourhorn sculpin was much appreciated as an ingredient of fish soup. In the 1980s, the colourful and large eggs of the species were also discovered to be delicious and since then have been collected in some places, e.g. in the northern Gulf of Bothnia.
Vulnerability, threats and management: Because of their spiny head, fourhorn sculpin easily get tangled and stuck tight in gillnets. Since the 1970s, the species has been rare in the western Gulf of Finland and southwestern sea area. The same trend occurred once before, in the late 1940s. During both periods, the salinity of the Baltic Sea has been higher than average, which may have contributed to the decrease, as the species is adjusted to relatively low salinity. Another contributory factor may be the greater abundance of cod (Gadus morhua) due to the increased salinity. In both periods of weak fourhorn sculpin stocks, cod stocks have been very abundant. In recent years, the fourhorn sculpin has shown signs of increase in the sea area.