- Which fish live in the Baltic Sea?
- Why does the flounder have a flat body?
- Which fish are migratory?
The fresh water of the Baltic Sea is not suitable for many marine fish
Marine fish in the Baltic Sea face the same problem as other marine life: brackish water is too fresh for them. Many marine fish cannot reproduce well in brackish water. For example, in fish spawning in the open sea, the eggs remain floating on the surface in saltier water, while in brackish water, they sink to the bottom. At the bottom, the water is colder and lacks the oxygen needed for development. Typical marine fish in the Baltic Sea are Baltic herring, sprat, cod, flounder, and salmon. On the other hand, several freshwater fish species can live in brackish water, but for some of the freshwater species, the water in the Baltic Sea is too salty.
- Baltic herring
- European sprat
- Cod
- Shark
- Flounder
- Salmon
- Ray
- Tuna
Think!
- Why is the Baltic Sea poor in fish species?
The Baltic herring and the European sprat
Baltic herring and European sprat are smaller relatives of the herring that lives in the Atlantic Ocean. Both Baltic herring and European sprat live in large schools in open water. Sprat and juvenile herring feed on the zooplankton in the sea, while older herring also feed on benthic animals and small fish. The Baltic herring spawn in shallower and warmer waters near the coast, while European sprat stay offshore.
The Baltic herring is the most abundant fish in the Baltic Sea. It also makes up the largest share of fishermen's catch.
- About 15 cm long
- Their stomach is smooth
- Their stomach is rough
- 10–13 cm long
The flounder and the cod
As the life of the European flounder passes lying on the seabed, their body becomes flat. The flounder feeds on various shellfish and small crustaceans living on the seabed.
The Atlantic cod is a broad-headed and sturdy predatory fish that lives in the deeper waters of the Baltic Sea. The brackish water of the Baltic Sea is not an ideal place for them, as they need more dense saltwater to breed. In those years, when storms bring more saltwater to the Baltic Sea, cod spawn better.
- Atlantic cod is a predator.
- European flounders eat other fish.
- European flounders are flat fish.
- Atlantic cod's reproduction depends on the right salinity.
Think!
- How is the body shape of the flounder related to their lifestyle?
- Why is it not always possible for cod to reproduce successfully in the Baltic Sea?
Freshwater and migratory fish also live in the Baltic Sea
A variety of freshwater fish, such as pike and perch, live near the beach, where the water is fresher. Many fish from the Baltic Sea live in the sea itself, but migrate elsewhere to spawn. These are called migratory fish. For example, salmon and sea trout migrate to the rivers to spawn. European eels also have an interesting life cycle: they are fish with a snake-like body that migrate long distances to spawn in the Sargasso Sea, where adult fish die after spawning. Eel larvae migrate for the same length of time to the waters where their parents came from.
- Fish bred by transplantation.
- A fish that lives in salt water and spawns in fresh water or vice versa.
- A fish that migrates long distances to catch prey.
Salmon
Salmon from the Baltic sea are large and strong. Young salmon initially live in a river, feeding on small invertebrates. When they go to the sea, they start feeding on fish and grow quickly. Eventually, most return to the river where they hatched to spawn. Diseases, river pollution, illegal fishing, and dams hinder the successful reproduction of salmon. Wild salmon are considered an endangered species. Today, almost half of the salmon in the Baltic Sea comes from farmed fry that have been released into the wild.
I now know that…
Typical marine fish in the Baltic Sea are Baltic herring, sprat, cod, flounder, and salmon. A variety of freshwater fish also live near the shore where the water is fresher.
