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r " III Figure 64. Colorado squawfish/charalote, 36.0 cm in total length. The specimen is a hatchery-reared offspring (1974 year-class) of broodfish captured in the Green River basin of Utah. fishes after becoming longer than 75 to 100 mm. Adults eat other fishes and thus probe and wander extensively in search of food. A squawfish of 90 cm long or more must have devoured almost any other fish in the river. Squawfish spawn over gravel bars in channels of rivers in spring or summer, after water temperatures exceed 200 to 21 0 C. They often move long distances to reproduce, and return year after year to the same or a similar spawning area. Major runs in spring into the Gila River, well documented in old newspaper accounts, must have been related to spawning. Breeding squawfish become silvery above and creamy yellow on the belly with an intense array of bright golden flecks on the upper sides. Razorback suckers (Fig. 65) tended to occupy strong, uniform currents over sandy bottoms. They also lived in eddies and backwaters lateral to the river channels, sometimes concentrating in deep places near cut banks or fallen trees. Large adults approached or exceeded 75 cm in length and more than 5.0 kg in weight. A remnant population of large adults in Lake Mohave, Arizona-Nevada, spawns from late January through April over gravelly bottoms in relatively shallow water (Fig. 66). Males become dark brown to black on the back and develop a russet- to orange-colored lateral band and yellow belly. Coarse, sharp tubercles, which are horn- like outgrowths of skin, are developed on the anal, caudal, and pelvic fins, and on the caudal peduncle. These function to hold the female during the spawning act. Females that have spawned repeatedly may be scarred and abraded from contacts with males and with rocky bottoms. The eggs are adhesive and are deposited in spaces between gravels. They hatch in a few days and young move to the shoreline for a time. Despite successful reproduction, there is no evidence for successful recruitment of young fish into the Lake Mohave population for more than twO decades. Larvae mysteriously disappear before achieving 15 mm total length. The same situation a ppears to exist in other, riverine parts of the Colorado River basin, and the species is proposed for listing as endangered. Under natural conditions in streams, young fish must have occupied shorelines, then moved with growth into habitats similar to those just described for young squawfish. Razorbacks feed mostly from the bottom, but have elongated, "fuzzy" gillrakers and a subterminal mouth both characteristic of planktonic or detrital feeding habits. Remarkably little is known of the ecology of bony tail (Fig. 67), and they are almost gone in nature. A small population persists in Lake Mohave, but only a few have been recorded from the upper Colorado River in recent years. As with razorbacks, there are no records of successful recruitment of this species for many decades; specimens caught in nature all appear to be old (35-40 yr) adults. Bony tail are large, streamlined fishes that have long 32