Gila coerulea

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General Information
Common Name: 
Blue chub

Conservation Status in California: Class 3, Near threatened (Moyle et al. 2011). Blue chubs are still common within their limited range but continue to be threatened by changing conditions in the upper Klamath Basin.

Life History: 

Life History: Blue chubs are omnivorous, as indicated by the generalized body shape and tooth structure. Blue chubs collected from Willow Creek, Modoc County, in August 1972 (all one year of age, 29-59 mm SL) fed mostly (66% by volume) on aquatic insect larvae and flying insects, including chironomid midge larvae and pupae, water boatmen, and water fleas. In comparison, two-year-old chubs (61-109 mm SL) fed heavily on filamentous algae (68%) and larger aquatic and terrestrial insects (Moyle 2002). Blue chubs from Oregon were found to have a similar diet (Lee et al. 1980). Blue chubs grow rapidly in the first four years of life and mature at about 12-15 cm SL. Growth slows upon maturity but can continue to reach 38 cm FL (Scoppetone 1988). Blue chubs are long-lived. One individual at 34 cm FL was aged at 17 years (Buettner and Scoppetone 1991). Little has been published on the growth of blue chubs or on its early life history.
Spawning occurs in May through August over shallow rocky areas at temperatures of 15-18EC (Lee et al. 1980). In 1966, C.R. Hazel documented their spawning behavior in Upper Klamath Lake, Oregon: "On the afternoon of May 4, 1966, I observed an estimated 200-300 blue chubs spawning at the shoreline on the northern end of Eagle Ridge. Spawning was taking place from near the surface to a depth of 0.3 to 0.5 m. The bottom was composed of large gravel and rubble of volcanic origin. The water was clear with a low concentration of blue-green algae . . . the water temperature was 17?C. Two to several males would approach a female and exhibit rapid and violent agitations of the water, making it impossible to see exactly what was taking place. In some instances the female was pushed from the water onto dry land and in a few situations, eggs were spawned outside the water. After these activities, egg masses were found attached to [submerged] rocks either on the sides or near the bottom edge. Many of the depositions were found along rocky edges at depths to 0.5 m.” Blue chubs gather to broadcast spawn in large schools in the summer months (ODFW 1996). As many as 30,000 eggs may be released in one spawning event. Spawning usually occurs adjacent to shorelines over gravel substrates in shallow (

Habitat Requirements: 

Habitat Requirements: Blue chubs are most abundant in habitats with warm (summer temperatures >20?C), low-velocity waters and mixed substrates (Bond et al. 1988). In the wild, they have been collected in waters as warm as 32?C (D. Markle, Oregon State University, pers. comm.). They are especially abundant in lakes but they school conspicuously in a variety of habitats, including small streams, shallow reservoirs and deep lakes. Although found in perennial and intermittent sections of Boles Creek, a tributary to the Clear Lake Reservoir (Modoc County), they are most common in the small, shallow, weedy reservoirs of the larger streams (Scoppetone et al. 1995). In Upper Klamath Lake, Oregon, they are (or were) most abundant in rocky shore and open water habitats, avoiding marshy shore areas (Vincent 1968). In the summer, they are thought to be excluded form the deeper parts of the lake due to oxygen depletion but move into them as oxygen levels rise (Vincent 1968).
Although wild blue chubs are often observed in warm water, laboratory studies have shown that they lose equilibrium at temperatures of 28-33?C (mean, 31.5?C) and oxygen levels of 0.6-1.5 mg/L at 20?C (Castleberry and Cech 1993). These tolerances suggest that increasingly degraded water quality can limit their distribution and cause a decline in abundance and viability (Castleberry and Cech 1993). One other study also found blue chub distribution was inversely related to dissolved oxygen concentrations (Vincent 1968).


Distribution: Blue chubs are widely distributed in the lower elevations of the upper Klamath and Lost Rivers in Oregon and California. In California, they are also found in Clear Lake, Lost River, Lower Klamath Lake, Tule Lake, and the canals and tributaries that feed them. Their distribution has expanded to include Iron Gate and Copco Reservoirs of the Klamath River (CH2M Hill 2003). Their distribution has also expanded through introductions in Oregon (e.g., Paulina Lake; ODFW 1996).

Abundance Trends: 

Abundance: Blue chubs remain common in Upper Klamath and Agency Lakes, Oregon (Simon and Markle 1997). They also remain abundant in the Boles Creek watershed and Clear Lake Reservoir (Buettner and Scoppetone 1991, Scoppetone et al. 1995). Between 0.2 and 3.2% (n = 70 – 196) of the fishes collected from Iron Gate, Copco and J.C. Boyle Reservoirs are blue chub (Desjardins and Markle 2000, CH2M Hill 2003). No systematic estimates of past or present abundances have been made.


Description: Blue chubs resemble Klamath tui chubs, with which they are usually associated, except that they have finer scales (58-71 in the lateral line), are not as deep bodied, have longer fins, and have pointed heads with larger mouths, with the maxillary reaching the eye. There are 9 dorsal rays, 8-9 anal rays, and 14-17 rays in each pectoral fin. The pharyngeal teeth (2, 5-5, 2) are sharp, slightly hooked and located in two rows. The lateral line is curved ventrally. Blue chubs seldom exceed 40 cm SL and often have dark backs and silvery blue sides. Spawning males have blue snouts and bright orange tinges on their sides and fins.