Threespine Stickleback
  • Side view adult.
  • Side view adult.
  • Side view adult.
  • Top view adult.
  • Bottom view adult.
  • Head-on view adult.
  • Close-up flank.
  • Close-up head.
  • Close-up mouth and snout.
  • Close-up tail.
  • Close-up dorsal fin.
  • Close-up anal fin.
  • Close-up pectoral fin.
  • Close-up pelvic fin.
  • Close-up dorsal spines: There are 3 (rarely 2 or 4) unconnected dorsal spines of dissimilar size, the first two are always larger.
  • Notice the smaller third spine and 9-11 dorsal rays; the tail is rounded or square; the anal fin has 9-11 rays and one anal spine.
  • Note the three dorsal spines, the solid color body pattern, and the lack of scales.
  • Close-up tail and anal fin: The tail is rounded or square, the caudal peduncle is narrow. The anal fin has one spine and 9-11 rays.
  • Close-up flank: The flanks show bony plates covering the sides.
  • Close-up pelvic fin: The pelvic fin has one single spine and one inconspicuous ray.
  • Close-up flank of a female breeder: Females show a pinkish color ventrally; the males are red ventrally with blue eyes (no photo).
DescriptionSimilar Species
Sticklebacks (Gasterosteidae)
Mouth and snout: Terminal to slightly superior and oblique, with minute teeth on upper and lower jaws. No barbels. Body patterning, color, and scales: Solid silver, gray, or tan, grading from dark on back to whitish on belly. No scales, but usually with 30 or more small bony plates that cover the sides. However, some populations are incompletely plated. Fins not distinctly pigmented. Body shape and size: Body fusiform in side view and laterally compressed. Typically 35-65 mm (1.5-2.5 in) TL; maximum in Wisconsin about 75 mm (3 in).
Tail, dorsal and other fins: Rounded or square tail. The dorsal fin consists of 2-4 (usually 3) unconnected spines followed by a fin with 9-11 connected rays. The first two spines are substantially larger than the third (or fourth if present). Pelvic fins thoracic and reduced to a single spine and ray. No adipose fin. Anal fin with 1 spine and 9-11 rays.
Distinguishing Characteristics
The threespine stickleback has 2-4 (usually 3) unconnected spines on its back, with the first two spines much larger than the third (or fourth if present). See also similar species information.
Breeding Adults
Breeding males have red on lower sides and belly and blue eyes; breeding females have more pinkish hues on lower sides and belly (photos).
Similar to adults.
None known from Wisconsin.
Compare Similar Species
Spines on Back
Stickleback, Brook4-6 (usually 5), simiarly sized and unconnected
Stickleback, Ninespine8-11 (usually 9), similarly sized
Stickleback, Threespine2-4 (usually 3), differently sized; first two spines much larger than the third (or forth if present)
Similarity Index
Stickleback, BrookModerately similar
Stickleback, NinespineModerately similar
Stickleback, ThreespineN/A