Effect of temperature, salinity, and feeding on somatic growth, otolith growth, and pigmentation of Japanese glass eel Anguilla japonica
Date Issued
2010
Date
2010
Author(s)
Chang, Bo-Jhih
Abstract
Glass eel of Anguilla japonica migrating in the open ocean will encounter with different environmental factors such as temperature, salinity, and starvation, which might affect the glass eel’s status such as somatic growth, otolith growth, and pigmentation stage. This study aims to determine the effect of temperature, salinity, and feeding on somatic growth, otolith growth, and pigmentation of the glass eel. Fish were immersed with alizarin complexone (ALC) then reared at different salinities (35, 26, 17 and 0 psu) under feeding or unfed conditions. To test the effect of temperature, glass eels were reared at 20, 15, 10 and 5 ℃ under unfed conditions. The results of this study indicated salinity appears no strong effect on pigmentation and somatic growth. Because the pigmentation stage at different salinities under feeding or unfed conditions was more advanced compared to the initial group but there was higher percentages in stages VIA4 in fresh waters than in seawaters. TL and W was significantly growth under feeding conditions compared to the initial values but no significant difference was observed in somatic growth among various salinities. And with food supply, there were higher percentages in later stages VIA3 to VIA4 than the unfed groups. The mean otolith growth increment per days of glass eels reared under unfed conditions was significantly lower (0.7757 ± 0.0941 μm/d) than under feeding conditions (1.0703 ± 0.2454 μm/d) of glass eel reared at different temperatures ranges from 149.83 ± .08 μm to 196.21 ±12.46 μm and the mean otolith radius was increased as the temperature elevating compared to the initial value (133.02 ± 9.46 μm) after 1 and 2 months. The pigmentation stage was more advanced into late stage with the temperature was increased, but glass eels reared at 5 ℃, the pigmentation stage developed slowly and remained in early stages VA to VB after 1 or 2 months. According the result of this study, otolith growth and pigment formation of the glass eels were strong affected by temperature and feeding, but these were not affected by salinity. In the wild, when glass eels encounter starvation conditions and low temperature, their somatic growth, otolith growth and pigment formation are significantly slowed down, resulting in delayed the upstream migration time and underestimated the daily age of the glass eels.
Subjects
otolith growth
pigmentation
temperature
salinity
feeding
Type
thesis
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