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12 Sedywick-Rafter cell), and measured (maximum body length and width) at 35-450 X under light microscope. Foods of larval suckers were analysed in the same manner after removal from the digestive tract. Zooplankton was qualitatively similar, but quantitatively distinct, in Lake Mohave and in the Arizona Bay backwater; however, abundance estimates are highly variable due to patchy distribution in space and time, and sampling overlapped only 16 days during the period. Cladocera (Bosmina or Daphnia) were dominant in Lake Mohave (Fig. 6); adult Copepoda comprised most of the remainder, and Rotifera, Chydorus, Sida, and Ostracoda were rare. Total densities ranged from <100 to >7,500 individuals/m3, and along with community composition varied greatly (Fig. 6). Rotifera were predominant in the Arizona Bay backwater, followed by Daphnia, mature and immature Copepoda, and Bosmina (Fig. 7); Chydorus and Ceriodaphnia were scarce. Total densities generally were lower than in the lake and ranged to a maximum of only ca 1000/m3. Plankton sizes were similar in the lake and Arizona Bay backwater, with two notable exceptions (Table 2): Copepoda averaged 0.12 to 0.22 mm and Daphnia 0.15 to 0.18 mm longer in the backwater. Most razorback sucker larvae in Lake Mohave had empty stomachs (Table 3), probably because they had not yet developed fully functional mouths. Many individuals with empty guts had remnant or recently absorbed yolk sacs. Amorphous organic matter of unknown origin was the most frequent material in guts (Table 3). Next in occurrence were cladocerans (Bosmina, Daphnia, and Macrothrix [the last not collected in plankton samples]) followed by rotifers and copepods. Macrothrix is associated with vegetation and, unlike other animals in plankton samples and stomachs, is not generally limnetic (Pennak 1976). Thus, while