Any member of the fish family Gasterosteidae, order Gasterosteiformes. The body may be elongate, naked, or with bony scutes along the sides. Three to 16 well-developed isolated dorsal spines precede a normal dorsal fin having 6 to 14 rays. Additional identifying features are as follows: 12 or 13 caudal fin rays; a single spine and 1 or 2 soft rays in the pelvic fin; 3 branchiostegal rays; circumorbital ring incomplete posteriorly; epineurals present; and 28 to 42 vertebrae. A maximum length of about 18 cm (7 in.) is reached in Spinachia spinachia.