The feeding rate was estimated for yearling carp living in a small lake contaminated with low‐level radioactive wastes. The amount of 137Cs that must be ingested to maintain the equilibrium body burden of the carp was calculated from measured values for body burden, biological elimination rates, and assimilation factors. The radioisotope was ingested by the fish as an integral part of its food items. The amount of food consumed was estimated by measuring the concentration of 137Cs in the food items. An age and growth study and the weight‐length relationship are given for the carp. The estimate of the average daily food intake was 5.36 g wet weight (3.9% of mean body weight) consisting of 2.4 g detritus and 1.6 g algae for maintenance, and 0.82 g detritus and 0.54 g algae for growth. On an energy basis, 3.7 kcal were consumed for maintenance and 1.3 kcal for growth. Net and gross food conversion factors were 3.18 and 12.55, respectively, and the ecological growth efficiency was 0.08.

No abstract

Influence of substrate, macrophyte growth and detritus on macroinvertebrate standing crop (numbers and biomass) as well as seasonal variations in standing crop were investigated in a trout stream .Ephemeropterans showed no consistent relationship to substrate type, either in numbers or biomass. Numbers of dipteran larvae (primarily chironomids and simuliids) did not show a definite relationship to substrate size . But a larger biomass was associated with larger substrates . Higher numbers and biomass of trichopterans (including Helicopsyche borealis) were associated with larger substrates . Numbers of coleopteran larvae showed no relation to substrate size, but biomass was greater in large substrates . Biomass and numbers of water mites were generally associated with larger substrates, whereas no relationship was observed in plectopterans .Larger numbers and biomass of ephemeropterans, dipterans (chironomids and simuliids but no other dipterans) and trichopterans are associated with macrophyte beds ; this is attributed to drifting species and those that have summer generations . Macrophyte growth reduced numbers and biomass of H. borealis, but no differences were observed in coleopterans or plecopterans .A substrate/detritus substitution study was done under natural stream conditions. An area of relatively constant current and depth was selected from which eighteen sites were randomly selected . Gravel and detritus were removed and replaced with two distinct sizes of substrate and three different levels of detritus . This was a 2 x 3 factorial analysis design . Ephemeropteran numbers were significantly related to substrate type and detritus level, whereas biomass was only related significantly to substrate . Numbers of chironomids and other dipterans responded significantly to substrate manipulation . Biomass of dipterans other than chironomids was significantly related to substrate type but not detritus level and chironomid biomass did not respond to either manipulations .Trichopteran numbers responded significantly to substrate and detritus manipulations, whereas biomass was significantly related only to substrate type . Analysis of variance showed that coleopteran numbers did not respond significantly to either manipulation ; however, orthogonal contrasts showed that, within large substrate, medium detritus level was significantly different from high detritus level . Oligochaetes did not respond to either substrate or detritus manipulation . The responses of the organisms to manipulations are explained in relation to interstitial spaces and oxygen as well as the interaction between substrate type and amount of detritus .

Plexiglas plates were placed in laboratory streams and in a spring and removed at 2-to 4-day intervals to determine the increase in standing crop of periphyton.The instantaneous growth rate, calculated from the growth curve of periphyton on plates in the streams, was 0.51 g mea day-l as compared to an estimate of 0.60 g m-' day-' obtained by oxygen measurements for growth of periphyton on the stream bottom. The average growth rate of periphyton on plates in the streams over a single exposure period was 0.31 g m-' day-l. Under the conditions of this experiment, the instantaneous growth rate was a better estimate of productivity than the average growth rate.

The productivity of algal communities was investigated in two recirculating artificial streams. Emphasis was placed on a study of the effects of various factors on energy flow and on the characterization of artificial streams as a research tool. Productivity was measured by pH and carbon dioxide changes, upstream‐downstream oxygen changes, and the biomass of algae collected on artificial substrata. A temperature increase caused a small, but insignificant, increase in net productivity, while increased light intensity caused an increase in net productivity. A higher current velocity caused an increase in net productivity, significant as shown by riffle vs. pool communities, but not significant between a fast and a slow stream. A shorter, but more frequent photoperiod did not change the rate of production significantly. High chelate concentration caused a reduction in net productivity. Estimates of net productivity by the carbon dioxide and oxygen methods were in agreement for two out of five studies, while estimates by the biomass of algae on substrata were consistently lower than estimates by the gas methods. Net production varied from 2,815 to 5,565 cal m−2 day−1, resulting in efficiencies from 3.8 to 9.8%. Efficiencies of gross productivity varied from 6.4 to 16.1%.