Springtime means eggtime

Spring is a truly busy time in the sea. When the ice cover melts in the Bothnian Bay it’s time for the fish to spawn and lay their eggs in the shallow bays, creeks and lakes.

A person with a snorkeling gear preparing a SUP-board on a bank.
The eggs can teach us a lot about the importance of coastal habitats and the lives of fish. Where do they lay their eggs? At what time? At what water temperature? By using snorkeling gear we can easily search and photograph them and the SUP board aids transportation. Photo by Linnea Bergdahl, County Administrative Board of Norrbotten.

The perch (Perca fluviatilis) is one of the most common fishes in and around the Balitc Sea and the Bothnian Bay. It lives both in freshwater lakes and streams as well as in the brackish coastal waters. In spring to early summer it comes to the shallow waters where the female lays her eggs. The eggs are encased in a gelatinous coat, up to one meter long band. To prevent the eggs from drifting away they are attached on vegetation. For example tree branches, stems, and old reed thus become important structures for the survival of the eggs.

Perch's eggs attached to reed straws.
The perch can lay up to 20 000 eggs in one cluster. Here they are firmly wrapped around reed to be held in place. Photo by Petra Pohjola, County Administrative Board of Norrbotten.

After approximately 2-3 weeks the eggs hatch. It depends on the water temperature though, the warmer water the quicker they hatch. The young perch spend their first time in sheltered, shallow areas where they feed on plankton. As they grow bigger they move out to deeper waters. Then they also start feeding on insect larvae, small crustaceans and smaller fish. The perch can become up to 20 years old.

Not all fish roe is as easy to identify as the perch’s white “bands”. These small, pearl-like eggs were found attached on stalks of various vegetation, but who they come from we have no idea of!

Small white eggs attached to straws one by one.
What specie does these small, pearl-like eggs belong to? Photo by Petra Pohjola, County Administrative Board of Norrbotten.

The only way to find out is to collect some of the eggs and let them hatch.  The hatchlings can then be identified by specie. Answer to come!

A glass flask filled with water and the eggs.
Waiting for eggs to hatch… Photo by Linnea Bergdahl, County Administrative Board of Norrbotten.

Written by Linnea Bergdahl, County Administrative Board of Norrbotten


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