| Summary: | <i>Deiratonotus japonicus</i> (<i>D. japonicus</i>) inhabits isolated locations and upstream brackish waters from Kanagawa Prefecture to Okinawa Prefecture in Japan. This species faces the threat of extinction because of changing habitat conditions. Our previous studies have shown that its complete larval development from hatching to metamorphosis consists of five zoeal stages and one megalopal stage. In this study, the effect of temperature on the survival and growth of larval development in <i>D. japonicus</i> under controlled laboratory conditions of 13, 18, 23, 24, 25, and 26 °C was investigated by rearing larvae (30 PSU; 12:12 h light/dark cycle; fed a diet of <i>Brachionus plicatilis rotundiformis</i> and <i>Artemia</i> sp. nauplii). The survival rates and developmental periods were measured for each larval stage. The highest survival rates were obtained at 18−24 °C. Metamorphosis to megalopa occurred at 23−25 °C. There were rapid and synchronous developments at 25−26 °C but delayed and extended developments at 13 °C. The molting period decreased with increasing temperature. With decreasing temperature, the beginning of the development and duration of molting was prolonged. In addition, there were very low survival rates at 13 °C and 26 °C in all zoeal stages. Our results indicate that the early larval stages of <i>D. japonicus</i> are well adapted to 18−24 °C, the range observed in the estuarine marine environment of the Kita River during the breeding season. Optimum larval survival and growth were obtained at 23 °C. Temperature significantly affected the survival rate, developmental period, and molting of the larvae. The relationship between the cumulative periods of development from hatching through individual larval stages (<i>y</i>) and temperatures (<i>T</i>) was described as a power function (<i>y = a × Tb</i>).
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