Ecological Effects of Ulva pertusa in Recirculation Culture System of the Prawn Penaeus japonicus.
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概要
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Study on the homeostasis of ecosystem in the poly culture of kuruma prawn <I>Penaeus japonicus</I> and marine macro-algae <I>Ulva pertusa</I> had been conducted outdoors in four groups of tank. The study aimed to investigate the effects of <I>U. pertusa</I> var. on the survival and growth of prawn and the water quality. Each group consisted of three 100-l tanks (namely tank-1=t-1, t-2 and t-3) . T-1 used for prawn culture ; t-2 and t-3 used for <I>U. pertusa</I> culture. Seawater was recirculated using airlift power. Initial number of prawn was 12 pcs/group. The stocking density of <I>U. pertusa</I> was 0g (Group-A=G-A), 100g (G-B), 300g (G-C) and 500g (G-D) .<BR>Results showed that the survival rate of prawn was 83, 92, 100 and 100% for those cultured in G-A, G-B, G-C and G-D, respectively. Weight increment of prawn was 50.1, 64.6, 81.5, and 93.0g for those cultured in G-A, G-B, G-C and G-D, respectively. Daily growth rate of prawn was 0.54, 0.67, 0.80 and 0.87% for those cultured in G-A, G-B, G-C and G-D, respectively. The food conversion ratio was 3.1, 2.9, 2.3 and 2.0 for G-A, G-B, G-C and G-D, respectively. Total production of <I>U. pertusa</I> was 1567, 1944 and 2160g in the G-B, G-C and G-D, respectively. The plant (<I>U.pertusa</I>) and animal (<I>P.japonicus</I>) production ratio was 24.3, 23.9, and 23.2 for the G-B, G-C and G-D, respectively. The average concentration of NH<SUB>4</SUB>-N was 88.2, 31.2, 19.9 and 15.7 μg-at⋅l<SUP>-1</SUP> in the G-A, G-B, G-C and G-D, respectively. The average concentration of NO<SUB>2</SUB>-N was 15.7, 3.7, 2.6 and 0.9 μg-at⋅l<SUP>-1</SUP> for the G-A, G-B, G-C and G-D, respectively. The average concentration of NO<SUB>3</SUB>-N was 32.2, 19.3, 4.5 and 4.2 μg-at⋅l<SUP>-1</SUP> in the G-A, G-B, G-C and G-D, respectively. The average concentration of Total-N was 182.6, 133.2, 125.8 and 107.3 μg-at⋅l<SUP>-1</SUP> in the G-A, G-B, G-C and G-D, respectively. The average concentration of PO<SUB>4</SUB>-P was 29.8, 11.2, 9.4 and 8.2 μg-at⋅l<SUP>-1</SUP> in the G-A, G-B, G-C and G-D, respectively. The average concentration of Total-P was 55.0, 15.8, 12.4 and 14.4 μg-at⋅l<SUP>-1</SUP> in the G-A, G-B, G-C, and G-D, respectively. The average dissoloved oxygen (DO) was 5.1, 5.4, 5.5 and 5.5mg⋅l<SUP>-1</SUP> in the G-A, G-B, G-C and G-D, respectively. The average pH was 8.28, 8.64, 8.82 and 9.00 in the G-A, G-B, G-C and G-D, respectively. The average water temperature was 29.1, 29.0, 29.0 and 29.1°C in the G-A, G-B, G-C and G-D, respectively.<BR>The present study proved that the presence of <I>U. pertusa</I> in recirculation cultured system of <I>P. japonicus</I> showed possitive impacts. To some extent, the survival and growth of prawn increased as the response of increment in stocking density of <I>U. pertusa</I>. The DO as well as pH were also increased as the same response. Moreover, the <I>U. pertusa</I> played important role on suppressing the eutrophication which was caused by the prawn excreted materials and uneaten feed. The nutrient concentrations decreased as the response of increment in stocking density of <I>U. pertusa</I>. The higher the stocking density of <I>U. pertusa</I>, the lower the nutrient concentration. The optimum level of stocking density of <I>U. pertusa</I> seemed to be 1g⋅l<SUP>-1</SUP> seawater. We suggest that <I>U. pertusa</I> can be used as a cleaning-agent in closed culture system.
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