Three-spined stickleback
Otolith description
Otoliths of gasterosteidae are very small and otolith length does not exceed 1 mm. The general otolith shape is round. The sulcus runs along the length of the otolith, over about of the total length. The sulcus is open at the ostium and closed at the cauda. Ostium and cauda are not distinguishable. The surface of the dorsal area is irregular, while the ventral area is smooth. The outside and margins are smooth. The ventral margin is straight while the dorsal margin is rounded. The rostrum is rounded, the antirostrum is indistinct. In some specimens a sharp protruding point may be visible above the rostrum.
The inside is flat and the outside concave.
Otoliths of three-spined stickleback are easily confused with otoliths of nine-spined stickleback Pungitius pungitius. Otoliths of nine-spined stickleback are more triangular than round.
Since otoliths of gasterosteidae are very small they are easily missed in samples, however the spines of the sticklebacks are much larger, diagnostic and fairly wear-resistant. Therefore the spines are easier to find and thus often used for determination.
Spine description
The spines of three-spined stickleback have a spined ventral and dorsal margin and rows of spinelets running along the length of the outside of the spine at the outside. The inside is smooth. The spines are usually straight, but the point is often bended or hooked, particularly in pectoral spines. Three types of spines can be distinguished. There are two large dorsal fin spines and a left and right pectoral fin (or ventro-lateral) spines. Furthermore, there is a small (third) dorsal spine and a small anal spine, both unsuitable for relating spine size to fish size. The large dorsal and pectoral spines can be distinguished by the joint side. The intrusion in the joint of the dorsal spine is straight, while in the pectoral spine is pointing down. The ventral and dorsal side of the dorsal spine are mirror images, while the pectoral spines have a protruding lobe at the dorsal side of the joint and are thus asymmetrical.
The spines can be easily confused with nine-spined stickleback spines. Nine-spined stickleback spines do not have spinelets at the outside and the margins are less spined. The spines of nine-spined stickleback tend to be concave at the inside while three-spined stickleback spines are flat. Spines >4.5 mm in length are always of three-spined stickleback.
When eroded the outside and margins are smoothed and the intrusion at the joint becomes wider.
Fish length and distribution
Three-spined stickleback can grow up to 10 cm in marine waters, while in fresh water they can grow up to 8 cm. Three-spined stickleback is (GASTACUL.TIF) found in fresh water and coastal waters. It forms schools outside the spawning season, particularly during the pre-spawning season (February to April). Spawning takes place in fresh water in spring. In early spring the fish migrate to fresh water, huge schools are formed in front of sluices that allow water flowing out, but prevent fish migration towards fresh water. Three spined sticklebacks are pelagic, while adults are found in schools near the bottom (Wheeler, 1978, Nijssen and De Groot, 1987, Witte et al., 1991, Muus et al., 1999).
Three-spined stickleback is a very common fish found along the coasts and adjoining fresh waters of the Northern hemisphere except the arctic waters.
Sample origin
Northern part of the Netherlands and Western Wadden Sea.