Brook 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.
  • Dorsal fin in top view: Notice the five unconnected dorsal spines of similar size (rarely 4 or 6).
  • The tail is rounded or square, and the caudal peduncle is narrow.
  • Close-up dorsal fin: There are five unconnected dorsal spines of similar size (rarely 4 or 6).
  • Notice the five dorsal spines, the mottled body pattern, and the lack of scales.
  • Close-up pelvic fin: The pelvic fins each have a single spine and an inconspicuous ray.
  • Close-up anal fin: The anal fin has one spine and 9-10 rays.
  • Side view of a breeding male.
  • Side view of a breeding male (top) and a pregnant female (bottom).
  • Side view of a breeding male (top) and a pregnant female (bottom).
  • Top view of a pregnant female (top) and a male (below).
  • Side view of a pregnant female.
  • Breeding males get very dark, sometimes jet black.
  • Alternate side view.
  • Alternate side view of two fish.
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: Mottled with irregular blotches, blotches often faint so appearing to be solidly colored; olive, greenish-gray, brown, or black with lighter colored blotches, cream on belly. No scales, but 30-36 small bony plates along lateral line. Fins variably pigmented. Body shape and size: Body fusiform in side view and laterally compressed. Typically 35-65 mm (1.5-2.5 in) TL; maximum about 85 mm (3.5 in).
Tail, dorsal and other fins: Rounded or square tail. The dorsal fin consists of 4-6 (usually 5) unconnected spines of similar size followed by a fin with 9-11 connected rays. Pelvic fins thoracic and reduced to a single spine and ray; pelvic fins possibly lacking in some populations. No adipose fin. Anal fin with 1 spine and 9-10 rays.
Distinguishing Characteristics
The brook stickleback can be distinguished by the 4-6 (usually 5) similarly sized and unconnected spines on its back. See also similar species information.
Breeding Adults
Similar to nonbreeders, but actively breeding males often solid jet black in life (black fades in preservative and fish appears mottled).
Similar to adults.
None known from Wisconsin.
Compare Similar Species
Spines on Back
Stickleback, Brook4-6 (usually 5); similarly 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, BrookN/A
Stickleback, NinespineModerately similar
Stickleback, ThreespineModerately similar