Relationship between growth
and biochemical indices in laboratory-reared juvenile Japanese flounder (Paralichthys
olivaceus), and its application to wild fish
M. Fukuda, H. Sako, T. Shigeta, R. Shibata-2001
Marine Biology, 138 (1): 47-55
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.
(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)