The mean total length of young-of-the-year paddlefish (Polyodon spathula) frown Lewis and Clark Lake (a main-ste•n Missouri River reservoir at the Nebraska-South Dakota border) was 215 •nm on 31 August of the first sramneT of life and estimated to be 296 •mn by the end of the first growing season; average growth rate was 2.7 mm/day. The diet in 1972 consisted of zooplankton and aquatic and terrestrial insects. Daphnia pulex was by far the most important food occurring in stomachs of all 79 fish 30-149 •mn long. Aquatic insects were i•nportant in late June and early July, and in August. The kinds of insects found in the stomachs suggested that the young fish fed at night in open water, near the surface. Paddlefish (Polyodon spathula) are native to the Missouri River and are present in all six main-stem reservoirs (Bailey and Allurn 1962; Benson 1968). Gavins Point Dam, which impounds Lewis and Clark Lake, was closed in 1955. The reservoir is located on the Nebraska-South Dakota border.

Fecundity and seasonal changes in ova size and development, fish condition, and percentages of body weight contributed by gonads and mesenteric fat were studied for white bass (Morone chrysops) from Lewis and Clark Lake on the Missouri River, in 1969 through 1971. Spawning occurred in late May and early June; the average length of the season was 25 days. Females spawned only about 50% of their ova; large ova were shed during spawning and smaller ova were retained and resorbed by late July or early August. Maturation of new ova for the following yearˈs spawning began in early August, when only primary oocytes were present in the ovaries. The number of ova produced by fish of a given length declined progressively from 1969 through 1971. Fecundity was more directly related to length than to age of fish. Condition factors for both sexes were highest in November, remained high through May, declined after spawning, and reached an annual low in August. Percentages of total weight contributed by gonads were highest in May and lowest in August for both sexes. Percentages of total weight contributed by mesenteric fat were highest in August and September and lowest in June.

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A piscicide, 1,1′‐methylenedi‐2‐naphthol, is lethal to Ptychocheilus oregonensis and P. umpqua at concentrations 3 to 100 times more toxic to squawfish than to salmonids. Selectivity of the chemical varies with the tolerances of the species and its potency varies positively with concentration and temperature. For a thermal range of 18.3 to 10.0 C, the minimum LC100 is 0.006 to 0.015 ppm for P. oregonensis and 0.01 to 0.03 ppm for P. umpquae. Within these ranges the mean survival time varies from 6 to 31 hr for P. oregonensis and 6 to 20 hr for P. umpquae. In 96‐hour assays at similar temperatures, the maximum LC0 is about 0.3 ppm for Salvelinus fontinalis, 0.1 ppm for Oncorhynchus tshawytscha, and from 0.6 to 1.3 ppm for O. kisutch and Salmo gairdneri depending on the water temperature. One domestic sheep and two ducks showed no ill effects when forced to drink water containing 10 ppm of the chemical for 1 week. A field application in a small lagoon containing several species of fish killed only P. oregonensis.

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