The Peace/Williston Fish and Wildlife Compensation Program (PWFWCP)

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Largescale Sucker
Catostomus macrocheilus

What do they look like?

A large-scaled sucker with 12 to 17 (usually 13 to 16 rays) dorsal rays. In profile, the body tapers steeply back from the dorsal fin to the relatively narrow caudal peduncle (its depth usually less than half the width of the dorsal fin base). The snout is short and, when viewed from below, scarcely projects beyond the upper lip. In profile, the hind margin of the lower lips barely reaches the front half of the nostril, and there is contrast between the dark dorsal area and the white underparts. Spawning fish have a distinct black lateral band set below a pale greenish band.

Where do they live?

In B.C. largescale suckers are abundant in low to moderate gradient rivers. In upper Peace drainages they are common in the Crooked and Parsnip systems and less common in the Finlay system. In rivers this sucker is associated with relatively slow currents and often occurs in large aggregations in deep pools. Little is known about the seasonal or diurnal movements of adults in lacustrine environments, but in summer they are caught both above and below the thermocline. Except for spawning migrations, adult largescale suckers appear to be relatively sedentary.

In lakes, juveniles forage in deeper areas than the fry, but little is known about the seasonal or diel movements of juveniles and adults in flowing-water environments.

Young-of-the-year in lakes are most abundant in shallow water over rock and gravel substrates. They appear to avoid heavily vegetated areas. Less is known about the habitat use of young-of-the-year in flowing water. As water levels drop in late summer and autumn, young-of-the-year concentrate in shallow side channels. These areas usually have silt-covered gravel or cobble substrates and there is no vegetation. In the Parsnip River there appear to be seasonal migrations between tributaries and the main river.

What is their life like?

No detailed study of the life history of the largescale sucker is available for British Columbia. Typically, largescale suckers spawn in the spring, usually when water temperatures reach about 8 °C. In the Williston basin, largescale suckers were observed spawning in the outlet of Summit Lake (Crooked River) during the first week of June (water temperature 15 °C). Spawning occurs in both flowing water and lakes. In rivers and streams, riffles adjacent to areas of slower water are typical spawning sites. In lakes, spawning usually occurs in shallow water (<2 m deep) over areas of coarse gravel. Although there is no site preparation, the substrate is often cleaned and a shallow depression created by the thrashing of spawning fish. The eggs are adhesive. Some eggs stick to the gravel surface but the current carries others into crevices among and beneath the rocks.

Fecundity in largescale suckers varies between about 9,000 to 30,000 eggs. Development rate is temperature dependent and hatching occurs in about 20 days at 10 °C and at about a week at 16 °C. The newly hatched larvae are about 10 mm long and remain in the gravel until they are about 12 mm in total length. Feeding starts at about 15 mm.

Initial growth is rapid and by the end of their first summer the largest young-of-the-year reach a length of 65 mm. Apparently, growth slows as the animals approach sexual maturity (5-6 years for males and 6-9 years for females). Although adult suckers are notoriously difficult to age, one 620 mm female gave an unverified otolith age of 18 years.

What do they eat?

As adults, largescale suckers are benthivores but like many fish they begin life as planktivores. Early in life the mouth is terminal but eventually shifts to a ventral position and is clearly subterminal by about 20 mm. When the mouth is terminal, about 80% of their food consists of planktonic species (e.g., Daphnia, Cyclops, Bosmina, and various nauplii) but as the mouth shifts position, the diet changes to predominately benthic prey (Chydorus, chironomid larvae, and periphyton). Periphyton remains the dominant food throughout the juvenile and adult life-stages but aquatic insects, especially tricopteran larvae, are a major item in the diet of adults. Adults exploit seasonally abundant food sources (e.g., fish eggs and larvae in the spring) and, in winter, filamentous algae.

What is their distribution? The largescale sucker is a western North American species that ranges from the Nass and Peace rivers in the north to the Columbia River in the south. In B.C., largescale suckers are abundant throughout the Columbia, Fraser, Skeena, Nass, and upper Peace drainages. From the Fraser, they have colonized the upper portions of the Homathko, Klinaklini and Dean rivers. Apparently they never reached the northwestern and northeastern portions of the province and are absent from the Liard, Yukon, Stikine and Taku rivers. Although the largescale sucker is primarily an interior species, they reach tidewater in large rivers like the Fraser and Skeena and are regular inhabitants of tidal sloughs. Salinities in these sloughs can fluctuate from 0 to 6 ppt. This suggests that the largescale sucker has some salinity tolerance but apparently not enough to colonize coastal islands or coastal rivers adjacent to a source like the Fraser River.

View Peace Williston distribution map.