Influence of diet shift from formulated feed to live mysids on the carbon and nitrogen stable isotope ratio (δ ¹³C and δ ¹⁵N) in dorsal muscles of juvenile Japanese flounders, Paralichthys olivaceus

O. Tominaga, N. Uno, T. Seikai-2003

Aquaculture, 218(1-4) : 265-276
Abstract:

To estimate the accumulated food consumption of released fish, we investigated the temporal change in the stable isotope ratio of carbon (δ¹³C) and nitrogen (δ ¹⁵N) in dorsal muscles when the diet of Japanese flounder juveniles was switched from a formulated feed to live mysids. The average δ ¹⁵N of fish that fed on mysids ad libitum did not change during the experiment but the average δ ¹³C gradually increased from -20.70 ppt to -19.19 ppt after the diet shift. The δ ¹³C values at the start and at the end of the experiment were almost equivalent to the δ ¹³C of the formulated feed and mysids, respectively.

The relations between time after diet shift and the δ ¹³C of fish fed mysids at 2.2% BW/day (2.2% group) and 4.4% BW/day (4.4% group) were as follows: δ ¹³C=-17.25-2.03 exp(-0.04×t) and δ ¹³C=-17.18-2.09 exp(-0.05×t), respectively. The change in δ ¹³C of the 4.4% group was significantly greater than that of the 2.2% group (likelihood ratio test). Since the growth rate of Japanese flounder juveniles was extremely high and the δ ¹³C of the control group that was fed the same formulated feed during the experiment did not change, it was suggested that the change in δ ¹³C was mainly attributed to the growth rate of the fish.

The combination of stomach content analysis with the stable isotope study makes it possible to estimate the growth rate in terms of body weight and consequently, cumulative food consumption of individual fish after release using the rate of change in δ ¹³C.

(Faculty of Biotechnology, Fukui Prefectural University, Obama, Fukui 917-0003, Japan, e-mail: tominaga@fpu.ac.jp)

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