A superb fish the size of a small finger slips into the vegetation: blue eye, red belly, slate blue back. Exotic, installed in the living room aquarium? Not at all, the stickleback lives in our rivers, our ponds, busy building a comfortable nest for its young.
A small bony freshwater fish
The three-spined stickleback is a bony fish of the Gasterosteidae family. It lives in rivers with calm currents, but also in ponds, puddles and isolated waterholes, all over France. Common, ubiquitous, it walks its long body from 4 to 10 cm, with a greenish back, a silver belly, in the abundant vegetation, on muddy or sandy bottoms. On its sides, no scales, but bony plates; on its back a row of spines, three in Gasterosteus aculeatus; under its belly not fins but pelvic spines. And especially remarkable spring colors. In the male, only, which from March prepares for the mating rituals.
A colorful male
The arrival of spring announces for the male stickleback a new outfit, with bright colors. His throat, his flanks, will become orange-red, his back slate blue. And his eyes of dull gray become azure blue. The female doesn't change anything in her wardrobe, it is she who will choose the most attractive male, with the most attractive parade. The one who will fertilize the eggs. Prepared by dozens in the females, they are so numerous and so big that she grows spectacularly, up to 25% of her weight in addition. She will entrust them to the paternal care, particularly serious.
A safe and cozy nest
Not content with adorning himself with beautiful colors, the little male stickleback works for his offspring. He chooses a territory, in shallow fresh water, with dense vegetation. On the bottom, he builds a nest of intertwined plants, bound by a mucus of his own making. Until July he will watch for females. And will seduce them of a dance, parade of presentation of its body of male and its sure and cosy nest. The conquered female will then lay her eggs in the nest. And the male will chase her away immediately, to take care of his young. He watches over them, ventilates them by creating an oxygen-carrying current. 8 to 10 days later, when the young are born, he will still be there, ensuring their protection until they leave, carried away by the current to other territories.
Dreaded carnivores and sought-after prey
The young sticklebacks will disperse, forming small scattered groups from several nests. Carnivorous, they will feed on zooplankton, crustaceans, insects, larvae and adults, worms, fry... And will even practice cannibalism, devouring each other. Sometimes cited as harmful for their voracity, sticklebacks are themselves hunted. They seem to be formidable with their row of hard and sharp dorsal spines rising up during an attack, not to mention their lateral pelvic spines always ready to hurt. But some predators have been able to adapt: the kingfisher knocks it out before swallowing it, the spines at rest are always folded. The heron will prefer to crush it with its powerful beak. The egret gobbles it head on...
The stickleback is a common fish of our fresh waters, not well known despite its amazing habits. Often raised in aquariums, it offers a fascinating show, spring colors, nest building, ventilation of the young. But under the waters of our rivers, ponds, sticklebacks are in regression and are classified on the list of protected species in "minor concern".
