Life History of the Mountain Sucker, Catostomus platyrhynchus, in Montana

The life history of the mountain sucker, Catostomus platyrhynchus, was studied in southwestern Montana during 1966 and 1967. Most specimens studied were collected from two streams by seining or electrofishing. Annuli were determined on scales from 491 fish. Annuli were formed during early June. Growth history of mountain suckers was based on the calculated length at the last annulus for fish of a given age. Female mountain suckers were slightly longer than males after age five, and had greater longevity. Average lengths (mm) at the last annulus for mountain suckers of each age from the East Gallatin River with sexes combined were: I—60.5; II—98.7; III—115.3; IV—133.2; V—149.3; VI—164.6; VII—187.5; VIII—202.9; IX—220.8. Most spawning occurred during late June and early July. Males were mature at age 4 and females at age 5. Sexes were distinguished during the spawning period using secondary sexual characteristics. Number of mature eggs per female ranged from 990, for a specimen 131 mm in length, to 3710, for one 184 mm in length. Food was mostly unidentified materials, but diatoms and other algae were important items.