The aim of this study was to evaluate the ability of implementation of the circulating system in black seahorse (Hippocampus kuda Bleeker, 1852) culture. This study was conducted in Cat Ba island - Hai Phong province from June to September, 2010. The seeds used in this study were collected from Nha Trang to Hai Phong and acclimatized for 5 - 10 days before running of the real experiment. The experiment included 2 treatments with three replicates or Fish were reared in the circulating system equipped with the bio-filter tanks
(2): Fish were reared in the tanks with water exchanged daily at 30 percent of culture volume. The result showed that environmental factors are within the acceptable levels for growth and development of black seahorse. There were no differences in survival and growth of fish cultured in the two systems. Fish grown in the circulating system obtained the specific growth rate in term of total length approximately at 0.51 +/- 0.06 percent as compared to 0.048 +/- 0.035 percent in the other. A survival of 83 +/- 2.2 percent was achieved at the end of the experiment in the circulating system while it was 81 +/- 3.3 percent in the exchange water system. A biomass of 145 g/m3 was reached at the culture density of 100 pieces/m3. The outcomes of this study promote the possibility of using circulating system as a potential alternative for the conventional exchange water culture system particular in seahorse culture, and so far as a measure to deal with the challenges in the aquaculture industry like reducing water demand and environmental pollution.