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General Behavior: A schooling, pelagic fish. Primarily planktivorous but also consumes benthic invertebrates, detritus, fish eggs, and occasionally fish larvae [Gerdes and McConnell 1963; Ingram and Ziebell 1983]. Reproduction: Maturation.-Mature at 1-2 or 2-3 years of age. Most. do not live past 2 years, but have been reported to live up to 3-4 years. Maximum length 175-200 mm [Carlander 1969; Johnson 1970; Sublette et al. 19901. Spawning Requirements.-Spawn in spring (May-June) and possibly fall (September-November) [Carlander 1969; McLean et al. 1982]. Water temperatures during spawning range 14-23°C. Spawn in open water or near shore over aquatic plants [Carlander 1969; McLean et al. 1982; Sublette et al. 19901. Spawning Behavior and'Biology.-Synchronous, group spawner. Eggs are randomly deposited over a 3 to 4-week period in vegetated areas [Carlander 1969; McLean et al. 1982; Sublette et al. 19901. Often spawn in early morning to avoid predation [McLean et al. 1982]. Reported fecundity ranges 900-25,000 eggs, depending on size of female [Sublette et al. 1990]. Eggs and Young. Eggs are adhesive and have a maximum diameter of 0.75 mm. 'Incubation period is 3 d at 27°C. Total length at hatching is 4.1-4.4 mm. Larvae exhibit diel vertical migrations; near surface in daytime, dispersed through midwater and near bottom at night [Burns 1966; Taber 19691. Examples of Interactions with Native Colorado River Basin Fishes: ¦ None found. Options for Control in the Upper Colorado River Basin: Not considered a threat to the endangered fishes. Threadfin shad in the UCRB are restricted to Lake Powell and inflow areas; winter water temperatures in other parts of the basin are too cold. Threadfin shad constitute the primary food source for piscivorous fishes in Lake Powell that could prey on native fishes. 33