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

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Peamouth
Ptychocheilus oregonensis

What do they look like?

A large minnow (adults reach lengths of over 250 mm) with a relatively small mouth that never extends back as far as the front of the eye. There are small barbels at the corners of the upper jaws, and the dorsal fin usually originates in front of the pelvic fins. The caudal fin is slightly asymmetrical (the lower lobe is longer than the upper lobe) and deeply forked. Adults have two dark bands on the flanks. Breeding adults have red lips.

Young-of-the-year peamouth often occur in mixed schools with young redside shiners and pikeminnows. They are separable from young redside shiners by the relative position of the dorsal and pelvic fins and by pigment pattern. The dorsal fin in redside shiners originates well behind the origin of the pelvic fins. Young peamouth are distinguished from young pikeminnows by the absence of a dark spot at the base of the caudal fin.

Where do they live?

Peamouth occur in lakes, large rivers and, in the spring, in small streams. In lakes, habitat use by adults changes seasonally. Adults are closely associated with the bottom, often at depths of over 20 m. In the spring they move inshore to spawn, and in the summer they begin a daily migration that brings them towards the surface and inshore in the evening, with a reverse migration in the morning. In late fall they cease this diel migration and move into their winter habitat. In large rivers like the Peace, seasonal habitat shifts are not as well documented as they are in lakes.

In lakes juvenile peamouth school in littoral areas but usually in deeper water than the young-of-the-year. In rivers, juvenile peamouth show a strong preference for slow (<0.1 m/s), shallow (<0.5 m) water over fine substrates. In large rivers, they congregate near the mouths of tributary streams and as summer progresses; they often penetrate considerable distances up low gradient tributaries. In the fall, they return to the main river where they spend the winter.

In lakes, during the summer, schools of young-of-the-year peamouth are found in shallow littoral areas. These schools often contain mixtures of peamouth, redside shiners, and northern pikeminnows. Like adults, yearling peamouth often exhibit a diel migration, however, their daily migration is the reverse of the adult migration. The young school in shallow, littoral regions during the day, and disperse into deeper water at night.

What is their life like?

Apparently, in the spring, increasing water temperatures trigger peamouth spawning. The threshold temperature for spawning is about 9 °C. In the Central Interior, peamouth breed from late May (streams flowing into Summit Lake) to mid-June (Crooked River). Typically, spawning occurs in flowing water over clean gravel but some populations spawn in lakes on gravel beaches. Nonetheless, most lacustrine populations spawn in inlet or outlet streams. Some populations spawn at night but most spawn during the day.

Both lake and stream spawnings involve aggregations of fish. Over the course of the spawning period, each female spawns many times, and with many different males. The eggs are adhesive. As in most fish, fecundity is a function of body size and egg number is estimated to range from about 10,000-20,000 eggs. The eggs take about six days to hatch at 18 °C. The newly hatched fry are about 7 mm and strongly nocturnal.

Newly hatched peamouth begin feeding at about 9 mm and grow rapidly in their first summer. Depending on latitude and food availability, they are 35-60 mm long by the end of the growing season. Males reach sexual maturity in their third summer (2+) and most females mature a year later. The maximum recorded life span is 19 years.

What do they eat?

Young-of-the-year peamouth consume a variety of prey including organisms taken from both the substrate and the surface. In lakes, they feed heavily on planktonic crustaceans and chironomid pupae but also take some benthic organisms. In rivers, young-of-the-year peamouth forage heavily on benthic organisms (amphipods, benthic copepods, chironomid larvae, and oligochaetes) along with some water column prey. As they grow in lakes, peamouth take prey from the bottom (larvae and nymphs of aquatic insects), from midwater (plankton) and from the surface (winged insects). The largest size classes occasionally eat fish. In turbid rivers adult peamouth feed primarily on benthic prey but catch some winged insects off the surface.

What is their distribution? The peamouth is a western North American species. Its natural range is restricted to the Columbia system and adjacent drainages that received their fauna from the Columbia River. In B.C., peamouth are found from the Columbia system north to the Nass River. In the Interior, they penetrate to the headwaters of both the Columbia and Fraser systems, and from the upper Fraser system peamouth have colonized the Skeena system (and, through the Skeena, the Nass River) and the upper Peace system. Along the central B.C. coast, peamouth are present in the upper portions of the Klinaklini and Dean rivers.

View Peace Williston distribution map.