Reproduction and early life history of northern squawfish,Ptychocheilus oregonensis, in Idaho's St. Joe River

Synopsis

Reproduction and early life history of northern squawfish,Ptychocheilus oregonensis, was investigated in Idaho's St. Joe River from 1980–1981. Spawning occurs in large aggregations which mill near the substrate to broadcast eggs and milt. Males greatly outnumber females in the aggregations. Males mature at smaller sizes and younger ages, and exhibit slower growth and greater mortality than females, although females devote more resources than males to gonadal production. Spawning was observed in June and July at temperatures of 12 to 18° C and was restricted to sites with the unique combination of a gravel-cobble substrate free of sand and a bottom velocity of 0.4 m s⁻¹ or less. Juvenile northern squawfish schooled with other young cyprinids in sandy, zero-velocity, shallow-water margins of the river. Age 1 northern squawfish used deeper and more diverse microhabitats than juveniles. Growth of juveniles was rapid and variable during the first summer. During winter, average length did not increase and condition declined. Young northern squawfish ate a wide variety of crustaceans, aquatic insects, and terrestrial insects although individual fish tended to focus on one or two items. Diet breadth and food volume increased with age except in winter.