| Research Abstract |
Polyculture of fish and seaweeds is a benefical system in aquaculture. In spite of its importance from the ecological point of view, little attention has been given in polyculture system. This may be due to the fact that fish and seaweeds have different growth seasons ; fish grow in summer nd autum while seaweeds propagate in winter and spring. Previously, we found the culture techniques of sterile Ulva pertusa which grow in summer and autum as same seasons as fish growth. In the presesnt study, we have examined the polyculture of fish and seaweed, sterile Ulva pertusa.
The first experiment was conducted in the fish cage culture farm from August 1993 to February 1994 at the Azumacho Fish Seedling Center. Two cages, 7x7x7m, were employed, one for polyculture experiment and the other one for control experiment by the routine method. Three years old red sea bream Pagrus major, about 1750 individuals each, were cultured in each cage. The Chlorophyta, steriled Ulva pertusa was cultured by th
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e floating net system in the experimental cage. Dissolved oxygen and carbon dioxide were measured by Radiometer ABL-330.
Considering the value of pO2 in the control cage as 100%, pO2 in the experiment cge stands 109.1%. On the other hand, average pCO2 in the control cage as 100%, pCO2 in the experiment cage stands 96.1%. From the results mentioned above, it may concluded that the pCO2 in the experimental cage decreased to 4% while pO2 augmented up to 9% compared to those in the control cage.
The second experiment was also conducted in order to know the efficiences of light intensity and water temperture on growth of sterile Ulva pertusa as a foundamental study of "harmonized fish culture with environment" where substances were recycled through the alga. Tendency of low light and high light intensities were observed around the winter solstice and summer solstice, respectively. The highest value was 19.7 mol/m2/day around the winter silstice and 47.3 mol/m2/day around the summer solstice. In multiple regression analysis, multiple regression coefficient of 0.74 was obtained. Less
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