The bigmouth buffalo, Ictiobus cyrinellus, is the most important commercial species in Lake Oahe, a reservoir in the upper Missouri RIver. The population was dominated by three strong year classes (1959, 1960, and 1962). Successful reproduction appeared to be associated with flooding of shoreline vegetation during spring and early summer. Growth rate was high during the first few years of impoundment and then declined. Inasmuch as little such flooding is expected in the future, annual landings of bigmouth buffalo will probably continue to decline sharply.

Manipulation of photoperiods, combined with modifications by other environmental conditions such as temperature and salinity, can alter growth, smoltification, and sexual maturation of salmonid fishes by way of a neuroendocrine pathway. The extent of responses of salmonids to environmental changes, however, is restricted by circadian endogenous metabolic rhythms that cannot be completely overcome by external factors. The success of the manipulation of photoperiod depends primarily on four factors: the daily length and the duration of the light treatment; the season and time of day during which fish are exposed to light; the age, sex, size and species of fish; and the type of physiological response under consideration. Although gaps remain in the available information, salmonids apparently need systematically changing, intermittent periods of darkness for optimum long-term stimulation of growth, reproduction, and migration.

Stomachs of 1,064 alewives, 1,103 yellow perch, 246 spottail shiners, 288 trout-perch, 454 slimy sculpins, and 562 fourhorn sculpins from Lake Michigan were examined for food contents. Fish were sampled primarily from March to November and nearly all were caught at the bottom in the southeastern part of the lake near Saugatuck, Michigan. Pontoporeia was the most commonly reprented food item in the stomach contents of the fish examined, with immature midges, Mysis (a type of freshwater shrimp), copepods, cladocerans, fingernail clams and crayfish also being represented. Different species consumed different proportions of foods. Zooplankton was the principle food of alewives and spottail shiners, but was also consumed in small quantities by yellow perch and trout perch. Mysis was important to fourhorn sculpins, in addition to Pontoporeia. Immature midges were a major portion of spottail shiners and trout perch, also being consumed by alewives. Fish were often the most important food of yellow perch in the largest size category. Crayfish were a sizable portion of the diet of yellow perch on rocky bottoms, but sparingly on smooth bottoms. Spottail shiners also ate substantial numbers of fingernail clams.

Two formulations of the herbicide 2,4-D (2,4-dichlorophenoxyacetic acid) - the butyl ester (BE) and the propylene glycol butyl ether ester (PGBEE) -- had 96-h LC50's to cutthroat trout and lake trout ranging from 490 to 1,200 microgram/liter in static tests. A third formulation -- the isooctyl ester (IE) -- was not toxic to cutthroat trout or lake trout at concentrations below 60.000 microgram/liter. The butyl ester (2,4-D BE) was slightly more toxic than 2,4-D PGBEE, and the toxicity of both esters increased as water temperature decreased.

Significant changes have occurred in the distribution of trout in streams of Great Smoky Mountains National Park since 1900. By the mid-1970's the original range of the native brook trout had been reduced by about 70% and the species was relegated to suboptimal habitat in head water streams. Most of the stream sections lost by brook trout became the territory of the introduced rainbow trout, which in 1977 occupied about 80% of the Park waters. After 1950, brown trout introduced in State waters outside the Park established reproducing populations in some 50 miles of stream formerly occupied only by rainbow trout. If current trends continue, the recovery of brook trout in Park water may be difficult, if not impossible, and brown trout may occupy much of the territory now held by rainbow trout.