魚類の適応変異に関する研究 : I. メダカ(Oryzias latipes T. & S.)の塩水適応 : 第1報野外観察

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As the first step of the study on the adaptation of fishes to saline water, an ecological survey of the killifish (Oryzias latipes T. & S.) living in salt-pond at Kasaoka City, Okayama Prefecture, was performed. In order to know whether population composition was variable according to degree of salinity of environmental water, samples of killifish gathered at various spots different in salinity were dissected, their body lengths being measured. The main results obtained are as follows: 1) The range of variation of body length among individuals of a population seems to depend on the degree of salinity of water where they live. The fishes living in fresh water deposited eggs at the middle of March when water temperature became warmer than 18℃, and many fry could be observed at the end of this month. The variable range of body length of fishes collected at this season was 11-35mm. In June, a considerable number of young fishes were observed, and the range was shifted to 5-29mm. The frequency distribution pattern of body length reverted in September to the former pattern observed in March and this state was still observed in November(Fig. 2). On the contrary, at the spots of high salinity (27 to 32‰) in the salt-pond, during Septenber to March, populations were usually composed from individuals of 15-29mm in body length, 80% of which were 19-24mm (Fig. 3-A, B, C). This range is clearly narrower than that observed at fresh water areas. In rainy season (June), however, the salinity in the salt-pond decreased and the population living in the water of the highest salinity at this season (24‰) was found being composed from individuals of 8-34mm in body length (Fig. 3-D). Considering with the facts mentioned above and with other data obtained at various habitats of different salinities through a year (Figs. 4 and 5), it might be concluded that, the higher the salimity of the environment, so the range of frequency distribution of body length in a population becomes narrower. This phenomenon seems to be attributable to the different adaptability of fishes to saline water as their developmental stages vary. 2) Generally speaking, the fishes living in the salt-pond began spwning in June, which was 2 or 3 months later than the beginning of spawning of the fishes living in the fresh water areas. Under natural conditions, the salinity in the salt-pond was diluted considerably by rain in the rainy season of June, and this seemed to be responsible for the late biginning of spawning in the salt-pond.
社団法人日本動物学会の論文
1957-09-15

魚類の適応変異に関する研究 : I. メダカ(Oryzias latipes T. & S.)の塩水適応 : 第1報野外観察

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魚類の適応変異に関する研究 : I. メダカ(Oryzias latipes T. & S.)の塩水適応 : 第1報 野外観察

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魚類の適応変異に関する研究 : I. メダカ(Oryzias latipes T. & S.)の塩水適応 : 第1報野外観察