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63 A B o- so- ae- ao- so- _ ioo-o- S - xao- xao- ?E Sao- E Boo- > eoo- loo- eoo- eoo- ,ooo- noo- {.e Fig. 2. Size (volume)-frequency distributions expressed as percentage of zooplankters in the Lake Mohave water column (darkened, '_eft) _,^d ,., stomachs of larval razorback sucker from the reservoir (nnPn, rioht)• ± indicates <1%; index of selection, L. indicated where /L/ > about 10 (see text). A. Total zooplankton: water column n = 354 potential food items, larval stomachs n =165 food items. B. Bosmina: water column n =176 potential food items, larval stomachs n =149 food items. to and largely a function of their primary food, Bosmina (Fig. 2B). Arizona Bay Backwater Razorback sucker larvae were first captured from the Arizona Bay backwater on 7 March, 5 to 8 weeks after adults were stocked. Numbers in- creased quickly and remained high into April. Mean TL of backwater larvae (n = 367) was ini- tially similar to that of Lake Mohave fish (approx- imately 10 mm), but increased to >16 mm by late April when the largest specimen was 20.3 mm, similar in size to that achieved by hatchery-reared razorback in comparable time (Papoulias unpubl. data). Larvae in the backwater thus survived to grow nearly twice the size (middle postlarvae) of the largest (early postlarvae) wild individuals from the reservoir. Zooplankton species richness was greater in the backwater than in the reservoir, but the most abun- dant kinds were the same in both places (Table 2). Rotifers were relatively more numerous (more than 50%) and copepods less abundant in the back- water (Table 1). Total zooplankton density aver- aged 377 animals m-3, only about 25% that of the reservoir. Predominant foods of sucker larvae in the back- water included rotifers, cladocerans (Bosmina, Ceriodaphnia, and Daphnia) and copepods (Table 2). Dietary diversity was greater than in the reser- voir, and included individual animals of larger size (e.g., larval Chironomidae and Trichoptera). However, we found no evidence that mean size of ingested food increased as fish TL increased from <12 mm to ---20 mm. Backwater larvae showed positive selection for cladocerans (especially Bosmina) and strong negative selection for rotifers (Table 1). Among available foods, backwater larvae ex- hibited positive selection for zooplankters 50 to 399 x 10-4 mm3 and negative selection for those 10 to 14 x 10-4 mm3 (Fig. 3a). Positive selection was strongest for rotifers 25-29, Daphnia 100-299 and 1,000--4,999, and copepods 100-299 x 10-' mm', while strongest negative selection was for rotifers 10-14, Bosmina 100-199, and Daphnia 5,000- 14,999 x 10-4 mm3 (Figs. 3b-e). Discussion Zooplankton communities and larval razorback sucker diets were similar in Lake Mohave and in