Gasterosteus aculeatus Linnaeus, 1758, Europe.
OTHER COMMON NAMES
Head relatively small, with small upturned mouth anterior to the eyes; eyes round and somewhat large. Body about four times as long as it is deep, with slender caudal peduncle. Three strong spines precede the first dorsal fin (with 10–14 rays), the last of which is smaller and attached to the dorsal fin; the first two spines are very tall. Dorsal spines are widely spaced. Anal fin opposite soft dorsal fin, with one spine and eight to 10 rays. Pectoral fins ending at mid-body length, with 10 rays. Pelvics have strong spine and single ray. All spines can be locked into place or depressed. Caudal fin brush-shaped. Trunk covered by slender plates, with much variation in arrangement. Coloration silvery on sides and bluish black dorsally, with orange pelvic membranes. Males become more reddish when courtship commences and drab when it terminates. Reaches 3.5 in (90 mm) in length.
Widely distributed in temperate marine waters of the Northern Hemisphere but also in coastal rivers and lakes.
The threespine stickleback occurs in a wide variety of coastal habitats in both brackish and shallow marine waters. It can be captured occasionally in the open ocean as well. Typical habitats include tidal pools, coastal rivers and creeks, lakes, salt marshes, and protected coastal inlets. Adults typically are found in association with vegetation (e.g., eelgrass). Individuals may venture far out into the open oceans, as far as 621 mi (1,000 km) in the Pacific.
Many populations remain most of the time in the open sea, venturing into coastal habitats to spawn and die in their second or third years. They swim by “rowing” with their pectoral fins and are capable of strong swimming motions, such as those required to ascend rivers. Moderately social outside of periods of reproductive activity, when males become strongly territorial.
FEEDING ECOLOGY AND DIET
Eats a wide variety of invertebrates and larvae, including copepods, gammarids, rotifers, branchiurans, oligochaetes, insects and their larvae, and even eggs of other sticklebacks. Sticklebacks are preyed upon by numerous other fishes as well as water birds, such as herons, mergansers, gulls, and loons.
of this species has been studied in detail. Females from 2 to 2.8 in (5–7 cm) in standard length have between 116 and 838 eggs, measuring about 0.06 in (1.5 mm) in diameter; egg number increases with body weight. Before spawning, males establish a territory, building a nest on the substrate (which is accomplished by “gluing” together bits of vegetation with mucus and kidney secretions). The nest is complete when the male carves out a tunnel, at which time courtship begins. A dance is performed for a gravid female that has entered the territory, which consists of the male jumping toward and away from the female in a zigzag fashion, with spines erect and mouth open. Once a female is impressed, the male exhibits gluing
and fans the nest with his pectoral fins. He then zigzags back to the female, leads her to the nest, and points to it with his open mouth. The female enters the nest with her caudal peduncle protruding, allowing the male to begin quivering movements against her flank. After she has deposited her eggs, the male moves through the nest, fertilizing the eggs and expelling the female. He then pushes the eggs deeper into the nest, flattening the egg mass and repairing the nest at the same time, before fanning the eggs. The male attempts to induce other females to spawn in the same nest; the number of female partners may vary, but studies conducted in Quebec indicated that males having two or three female partners is the norm in that region. Incubation lasts roughly 14–20 days. After the eggs hatch, the male destroys the nest and guards the young (collecting any that may have fallen away). After his progeny become free-swimming, the male starts another courtship cycle.
Not listed by the IUCN.
SIGNIFICANCE TO HUMANS
Not a commercially important species. The threespine stickleback is studied intensely by fish ethologists. Often kept in aquaria, where it reproduces easily.
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