Ecological Investigations of a Freshwater Shrimp, Leander paucidens. (de Haan), in Lake Towada

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This investigations were done at Lake Towada during the summer (August 10 th-18 th, 1936) and the results may be surrrmerised as follows: 1) The freshwater shrimp, Leander paeeidens (de Elaan), is distributed in any coast of the lake. The relationship between its distribution and the condition of the bottom or the degree of the luxuriance of the algae was not distinct. 2) It increased in number from the coast to a depth of 25 meters, especially abundant in the area to a depth of 15 m and markedly decreased from the regions over 30 m. Whereas, the good fishing place of the shrimp is the area from the coast to a depth of 30 m. The thermocline of the lake is 10 m-15 m, at which the temperature is 10°C-15°C. We think that the shrimp seems to like and live in the area where the temperature is over 10°C. 3) The size of the male shrimp is smaller than that of the female and the biological minimum size of the latter was 3.78 cm. The size over 4.5 cm is almost occupied by the female. 4) The sex-ratio is different with depths. The percentage of the occurrence of the male to the female was 6% in the area to 5 m, and 71.06% in 24 - 52 m. The percentage of the incubation in the former was 94.3 % and that of the latter was 16.7%. 5) The difference of the size in both depths mentioned above is based on the sex-ratio. 6) The number of incubation increased directly proportional to the body length. The size of egg was 1.3-1.6 mm and increased with the growth of egg. It was independent on the number of the incubation. 7) The size of the shrimps captured by the shrimp-traps in summer was 1.8 - 6.3 cm (usually 4.0 -4.2 cm). They seemed to mature in one year and to survive after the oviposition.
日本陸水学会の論文

Ecological Investigations of a Freshwater Shrimp, Leander paucidens. (de Haan), in Lake Towada

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日本陸水学会 | 論文

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