Seasonal changes of the RNA/DNA ratio, size and lipid contents and immigration adaptability of Japanese glass-eels, Anguilla japonica, collected in northern Kyushu, Japan

RNA/DNA ratios and the condition factor, as determined by weight and length of glass-eels, Anguilla japonica, were evaluated for assessment of nutritional status. The negative correlation of RNA/DNA ratios and condition factor between capture months corresponded to an increase in DNA content and to a decrease in dry weight, respectively. These findings indicated that the body material decreased in the later caught glass-eels, but, in contrast, DNA content and ossification increased. These phenomena were explained by such factors as food density and metabolic energy requirements. We concluded that the development of the glass-eel with poor feeding is influenced by differences in ambient water temperature, and that expended endogenous nutrition originates in the leptocephali.