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4? ments of fin rays in all fins (35 mm). Specimens examined all had attained active swimming capa- bility (middle prolarvae), most were early postlar- vae, and the largest were middle postlarvae (termi- nology for razorback suckers from Minckley & Gustafson 1982). Jaws were formed and mouth and anus were open, all were thus presumed capable of feeding. However, yolk had not been completely assimilated by the smallest individuals, which may not yet have begun to feed. Adjacent to Arizona Bay is a backwater (Fig. 1) separated from the reservoir by a wave-formed spit of coarse gravel. This protected habitat was se- lected for rearing razorback sucker in isolation to preclude potential destruction of eggs or larvae by introduced fishes, indications of which had been observed in Lake Mohave and elsewhere (see be- low). The backwater had maximum depths of 1.7 to 3.7 m and surface areas of 0.85 to 2.10 ha at respec- tive reservoir elevations of 193.5 to 195.5 m, and was fed by reservoir water that freely exchanged through the porous berm. Water temperature par- alleled that of the reservoir, but averaged slightly cooler (-1.1° C) in winter and warmer in summer (+1.8°C); thermal differences were most pro- nounced on early winter mornings and late summer afternoons. Substrates were coarse gravel around margins and organic silt in deeper areas. Shallow regions were occupied by dense stands of water- milfoil (Myriophyllum spicatum) interspersed with curly leaf pondweed (Potamogeton crispus). Fishes which initially inhabited the backwater were threadfin shad (Dorosoma petenense), common carp (Cyprinus carpio), channel catfish (Ictalurus punctatus), mosquitofish (Gambusia affinis), largemouth bass (Micropterus salmoides), green sunfish (Lepomis cyanellus), and bluegill (L. mac- rochirus). All are non-native. These were removed by ichthyocide in autumn 1984, and the backwater stocked in January-February 1985 with 30 female and 150 male adult razorback suckers collected from Arizona Bay. These spawned successfully and produced larvae that were first captured on 7 March 1985 and subsequently monitored through their disappearance in early April (see below). Larval sampling in shallow littoral areas of both the reservoir and backwater was generally at night, when the small fishes were attracted to a spotlight, captured by dipnet, and preserved in 5% buffered formalin. Zooplankton in Lake Mohave was col- lected in duplicate Clarke-Bumpus samples (8011. mesh) towed for 5 min at 1.3 km hr-' and 0-3m depth throughout habitats occupied by larval suckers. Backwater samples were duplicate, com- posite 38-L grabs concentrated through 80 µ mesh. Zooplankters were preserved in 5% formalin and later identified, enumerated (Sedgwick-Rafter chamber), and measured (greatest body length and width) at 35-450x with a light microscope. Linear dimensions were converted to individual volume on the basis of similarity to regular geometric sol- ids. Foods of larval suckers were treated in a simi- lar manner after removal from digestive tracts. Selection of foods by taxon and size class (volume) was evaluated by a linear index: L = r; - p;, where r; and pi are relative abundances expressed as pro- portion of prey item i in the gut and habitat, respec- tively (Strauss 1979, 1982). The index ranges from -100 to +100. Positive values indicate preference, negative values avoidance or inaccessability, and values near zero indicate random feeding. We con- sidered /L/ <10 not different from L = 0. Results Lake Mohave Razorback sucker larvae were first captured from Lake Mohave in Hammerhead Cove on 9 Febru- ary, approximately 3 weeks after initial observa- tions of spawning at that location. Larvae became abundant within the next few days and remained common into April. Larvae averaged 10.6 ± 0.3 (SE) mm TL (n = 410) throughout the period, in- dicating continuous spawning and larval produc- tion. There was no evidence of larval growth since neither mean nor maximum TL increased; the largest individual captured from the reservoir was 12.2 mm. Comparisons with known-age fish reared experimentally at similar temperatures (Marsh 1985, Papoulias unpubl. data) indicated maximum age of the largest specimens was at most a few weeks. 1