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<br />In life the adults have the ventral surface yellow to yellow-
<br />orange, the iris yellow, the lower third of the head including the tip
<br />of the snout orange-yellow, as contrasted with the flesh-colored
<br />mouth. The sides are pinkish to reddish brown, the back and top
<br />of the head is olive-brown, and the anterior ridge of the hump is
<br />pale olive. The dorsal fin is olivaceous, the anal orange-yellow, and
<br />the' caudal yellowish-olive; in some the fins may be rosy. When
<br />spawning, males are black on the back and sides down to a point
<br />about one inch below the lateral line, and brilliant orange from
<br />this point to the belly (Douglas, 1952).
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<br />Life History
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<br />In the spring, the humpback sucker migrates into tributary
<br />streams or moves to the shores of reservoirs to spawn. Spawning
<br />takes place in water between about 540 and 650 F. over silt, sand,
<br />gravel, Qr locks at depths of about 1 to 20 feet. One female is
<br />attended by 2 to 12 males, the group moving slowly in circles of
<br />three to five feet in diameter. Upon reaching a suitable spawning
<br />site, the female, closely pressed by a male on either side, settles
<br />on the bottom and starts to vibrate her body. When this act reaches
<br />a convulsive stage, the eggs and spermatazoa are simultaneously
<br />expelled. As this occurs, the three. fish move forward and upward,
<br />leaving a cloud of silt and sand as spawning is consummated. After
<br />resting for five to ten minutes, the female moves away but soon may
<br />be followed by males other than the two with which she just
<br />spawned. Some females have been observed to spawn with as many
<br />as three sets of males in reservoirs of the lower Colorado River
<br />(Jonez and Sumner, 1954: 67-68, 142-143). The females are larger
<br />than the males, and may also be recognized by the rough tubercles
<br />on their anal fins. The spawning act does not differ significantly
<br />from that of other species of suckers (Reighard, 1920). The eggs
<br />are transparent and adhere to the gravel and rocks where they
<br />have been deposited.
<br />The early life-history stages (postlarvae) may be distinguished
<br />from those of other suckers by the presence of a few, giant black
<br />pigment cells along the back (Winn and Miller, 1954, pIs. 3A, 4A).
<br />Food eaten by this species in the lower Colorado River con-
<br />sisted of algae and midge larvae (Jonez and Sumner, op. cit.).
<br />The humpback sucker reaches a length of about three feet
<br />and attains weights of 10 to 14, occasionally 16 pounds. It is known
<br />to hybridize with the flannelmouth sucker (Hubbs and Miller, 1953).
<br />
<br />107
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