Relationship between growth and biochemical indices in laboratory-reared juvenile Japanese flounder (Paralichthys olivaceus), and its application to wild fish |
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| Authors: | M Fukuda H Sako T Shigeta R Shibata |
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| Institution: | (1) National Research Institute of Fisheries Science, Yokosuka Station, Nagai 6-31-1, Yokosuka 238-0316, Japan Tel: +81-468-562887; Fax: +81-468-573075 e-mail: fukudam@nrifs-a.affrc.go.jp, JP;(2) National Research Institute of Fisheries and Environment Science of Inland Sea, Ohono-cho, Saeki-gun, Hiroshima 739-0452, Japan, JP |
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| Abstract: | In order to estimate growth rates based on biochemical indices of the liver of wild Japanese flounder (Paralichthys olivaceus), juveniles were reared at six ration levels (0, 0.5, 2, 4, 6 and 8% body weight day−1) in the laboratory for 14 days, and the relationship between their growth rates and biochemical indices (RNA/DNA, protein/DNA,
triglyceride/DNA, phospholipid/DNA and cathepsin D activities) were determined. Positive and approximately linear relationships
were seen between growth rates and the indices of RNA/DNA, protein/DNA and phospholipid/DNA. The triglyceride/DNA ratio decreased
with increasing growth rates up to approximately 1% body weight day−1, then increased linearly with increasing growth rates. There was no significant correlation between growth rates and cathepsin D
activity, and the highest values were obtained in the starved fish. Compared with laboratory-reared specimens, wild specimens
of similar sizes were found to have significantly larger livers. The RNA/DNA, protein/DNA and phospholipid/DNA ratios of wild
specimens fell in a broad range between ration groups of reared juveniles. The protein/DNA ratios of wild specimens were low
and outside the range of the reared juveniles at six ration levels. In contrast, the levels of cathepsin D activity of wild
fish were highest compared to the reared fish. Estimated growth rates of wild fish from the RNA/DNA, protein/DNA and phospholipid/DNA
regressions obtained from the rearing experiment were 1.66, −1.74 and 0.10% day−1, respectively. Based on our results, the RNA/DNA index may be regarded as the most valid and reliable growth estimator. It
is noted that the larger liver size, the lower liver protein/DNA ratio and the unexpectedly high level of cathepsin D activities
of wild specimens found in this study may reflect the different metabolic conditions of fish reared in the laboratory compared
to those collected in the field.
Received: 29 February 2000 / Accepted: 26 August 2000 |
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