In the present paper it has been discussed that the rate of production (productivity) of a species population, a trophic level and a whole community living in rivers differs according to the life history of species and to the intra- or interspecific relations. Some of examples which gave grounds for the discussion is as follows :
1) The rate of primary production of algae growing on stones may be influenced by the grazing effect of aquatic insects or fishes and by the density effects among algae.
2) The upper limit of standing crop and the rate of production of aquatic insects differs according to the faunal composition of them. The large standing crop (larger than 20 grammes per square metre) consisted only of that the net-spinning caddis-fly larvae (Stenopsychidae or Hydropsychidae) are dominant (Fig. 1).
3) One of the principal factors determining the standing crop of stenopsychian larvae is the morphometry of river confluent point, because the adult
Stenopsyche cannot migrate upstream into the tributaries where the water-surface do not continue at the point at which the water runs under the rocks, stones or sands (Table 1).
4) The fish-food relationships change according to the difference of the faunal complex of food animals or algae, and also of fish themselves. The food consumption and the food selection by fish also change according to such differences (Figs. 2 to 4).
5) The social structure of a fish species is also changeable factor to the food consumption and the rate of production of the fish. For example, Ayu fish behaved schooling can maintain the population about eight times than those behaved territoriality.
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