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Presentation 19<br />
BIOINDICATOR AND BIOFILTER FUNCTION OF Ulva spp. IN FISH FARM<br />
ENVIRONMENTS<br />
Hisashi Yokoyama * , Yuka Ishihi<br />
National Research Institute of Aquaculture, Minamiise, Mie 516-0193, Japan<br />
* Email: hyoko at fra.affrc.go.jp<br />
In order to examine the efficiency of Ulva spp. (Chlorophyta) as a bioindicator <strong>and</strong> biofilter for<br />
dissolved inorganic nitrogen discharged from coastal fish farms, field surveys <strong>and</strong> field<br />
cultivation experiments were conducted in Gokasho Bay, central Japan. Naturally occurring<br />
green algae Ulva spp. were collected in <strong>and</strong> around a fish farm in February, May <strong>and</strong> July, <strong>and</strong><br />
their δ 15 N <strong>and</strong> tissue N contents were analyzed. Values of these parameters obtained in May <strong>and</strong><br />
July decreased with the distance from the fish cages, suggesting that Ulva spp. occurring in close<br />
vicinity to the fish farm assimilated the fish-excreted N. To evaluate this uptake, we housed<br />
round cut pieces of thalli of Ulva ohnoi in transparent chambers <strong>and</strong> cultured them beside a fish<br />
cage <strong>and</strong> at a control station for 2 wks in May, July <strong>and</strong> September. The thalli cultivated beside<br />
the fish cage showed significantly higher specific growth rates (15.8–20.9%) <strong>and</strong> higher N<br />
assimilation rates (4.2–13.9 mg N g dry wt –1 d –1 ), which are among the highest levels known for<br />
seaweed biofilters. The high growth rates during the warm season <strong>and</strong> easy cultivation indicate<br />
the suitability of Ulva ohnoi as a biofilter.<br />
ANNOTATED BIBLIOGRAPHY OF KEY WORKS<br />
Hirata, H., S. Yamasaki, H. Maenosono, T. Nakazono, T. Yamauchi, <strong>and</strong> M. Matsuda. 1994.<br />
Relative budgets of pO 2 <strong>and</strong> pCO 2 in cage polycultured red sea bream, Pagrus major <strong>and</strong> sterile<br />
Ulva sp. Suisanzoshoku, Vol:42. Pp 377–381.<br />
Polyculture of fish <strong>and</strong> seaweeds is a beneficial system in aquaculture. In spite of its importance<br />
from the ecological point of view. Little attention has been given in polyculture system. This may<br />
be due to the fact that fish <strong>and</strong> seaweeds have different growth seasons: fish grow in summer <strong>and</strong><br />
autumn while seaweeds propagate in winter <strong>and</strong> spring. Previously, culture methods for sterile<br />
Ulva sp., which grow in summer as do fish was reported. Following those methods, in the present<br />
study interrelation between pO 2 <strong>and</strong> pCO 2 in polyculture cages of red sea bream, Pagrus major<br />
<strong>and</strong> Ulva sp. at the fish culture farm of Azuma-cho Fish Seedling Center was investigated. Two<br />
cages, 7 m X 7 m X 7 m, each containing 1750 three years old fish weighting about 654 g were<br />
used in this experiment. pO 2 <strong>and</strong> pCO 2 were measured by Radiometer ABL-330. Considering the<br />
value of pO 2 in the control cage as 100%, pO 2 in the experimental cage st<strong>and</strong> 109.1%. On the<br />
other h<strong>and</strong>, average pCO 2 in the control cage as 100%, pCO 2 in the experiment cage st<strong>and</strong>s<br />
96.1%. From the results mentioned above, it may concluded that the pCO 2 in the experimental<br />
cage decreased to 4% while pO 2 augmented up to 9% compared to those in the control cage.<br />
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