The Gasterosteus fish has three hard spines on its back: two long spines at the front and one shorter spine. Its body measures about 10 cm long; although this type of fish lacks scales, it possesses sturdy bony plates. Interestingly, the number of these bony plates increases as the water salinity rises.
Mature Gasterosteus fish inhabit river mouths and downstream areas, returning to freshwater regions for spawning during the spring season. However, some species of Gasterosteus spend their entire lives in freshwater. During the breeding season, male Gasterosteus undergo several changes: their eyes become sparkling blue, and their chest turns bright red or orange. With these vibrant colors, they begin to attract female Gasterosteus.
Male Gasterosteus build nests in depressions on the lake or riverbed. They use a sticky substance secreted from their kidneys to bind together underwater twigs and leaves to create the nest, which has an arched shape with a passage through it.
The male begins to fight off other male Gasterosteus to defend the nest and a small surrounding area, while simultaneously enticing passing females. The male performs attractive dances to captivate the females, encouraging them to swim through the nest he has prepared. As the female swims past, she will lay some or all of her eggs into the nest. Immediately afterward, the male swims through the nest to fertilize the eggs.
A male can attract multiple females to swim by his nest. In one breeding season, this nest can hold between 300 to 1000 eggs. The male entices the female and must “care for” and protect the eggs. The male Gasterosteus must frequently clean the eggs and use its tail to create a flow of oxygen-rich water over them. Additionally, it must carefully guard the eggs, chasing away any creatures that might attempt to eat them.
After about 4 to 27 days, depending on the water temperature, the eggs begin to hatch. The fry remain around the nest for about a week before swimming away.
Gasterosteus eat a variety of foods: crustaceans, worms, fish eggs, larvae,… and some types of plants. They also consume smaller fish.
Another noteworthy point: After the breeding season, Gasterosteus congregate into small schools in freshwater; while in the sea, they gather together to form large schools of Gasterosteus.
Gasterosteus prefer to live in clear waters with plenty of vegetation along ponds, rivers, or coastal areas. They are found across North America, Europe, and Asia.
