The marbled flounder (Pseudopleuronectes yokohamae) is a widely distributed, economically important demersal species in Japan. A study into the growth of marbled flounder in six sampling areas around Japan also found significant differences in otolith nucleus size (diameter of otolith opaque core area) among areas, warm areas showed the bigger nucleus size of otolith, and cold areas showed the smaller size. Based on the physical environmental factors, it was suggested that water temperature affected the nucleus size among these sampling areas. To investigate the factors that influenced the formation of opaque and translucent zones in otolith nucleus, we conducted a rearing experiment using juvenile fish at 122 days post hatch (dph). Fish were reared at salinity of 33‰ and different water temperatures (15, 20, 25 °C) from 138 to 213 dph. The otolith growth was correlated positively to water temperature. We also measured the relative greyscale values of the opaque and translucent zones during the period of rearing experiment in each otolith, which showed a negative correlation with water temperature. The results showed that there was a significant relationship between water temperature and otolith formation. The otolith of the marbled flounder will grow larger and have a higher matrix density at higher water temperatures.
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