Carl B. Schreck

Angler Oriented Objectives of an Aquatic Weed Control Program

Chiekahominy Reservoir, Virginia, was treated with a mixture of herbicides diquat and endothall to control obnoxious growths of Egeria densa Planchon. Herbicides were undetectable in water by the 16th day after treatment. Herbicides accumulated in plant tissue at levels higher than those in the water. Only diquat accumulated in hydrosoils. Diquat levels in hydrosoils increased as levels in plants and water decreased. All diquat had dissipated from hydrosoils after two years. Neither herbicide concentrated in edible fish flesh. Aerial photographic monitoring revealed the amount of surface...


An Evaluation of Catchable Trout Movement Using Two Marking Techniques

Two marking techniques, freeze branding and subcutaneous tags, were used to evaluate movement of catchable rainbow trout (Salmo gairdneri) stocked into Rich Creek, West Virginia. These marks proved to be a valuable tool in studies requiring both rapid recognition of marked fish and identification of individuals. In general, there was a marked movement of trout downstream from the point of release, even during periods of low water conditions. Mean distances moved in both directions were 465 meters downstream and 197 meters upstream, respectively.


Steroid Assays And Their Usefulness In Fisheries Research

Techniques used to quantify circulating levels or stcroid hormones in teleostean fishes may help solve problems in fisheries research. Competitive protein binding assay used to determine levels of androgens. corticoids. and radioimmunoassay for estrogens allow analysis of relatively large numbers of samples within a short period of time. Results obtained by these methods indicate that rainbow trout (Salmo gairdlleri) have endocrine responses to various stressors. Repeated bleeding causes a marked lowering of plasma androgens in the male while cortlcoids arc increased in both sexes....