| The increase for market demand on sea cucumbers has brought pressure on the aquaculture industry with the price of sea cucumber becoming lower. Sea cucumber(Apostichopus japonicus) is sensitive to water temperature, and adult individuals have estivation. Normally, sea cucumbers are easily affected by natural environment, which can lead to the high farming risk in long culturing periods. Industrialized recirculating aquaculture as a kind of temperature-controlled aquaculture mode has advantages of water saving and environment friendly. The study on industrialized recirculating aquaculture has economic and social significance for the aquaculture industry.Two sets of recirculating aquaculture systems(RAS) have been designed at the lab level, each one composed of four rearing tanks, four sedimentation tanks, a water treatment unit and a automatic control system. It can achieve automatic water treatment and water exchange during the breeding process. In addition, water temperature can be kept in a proper range, relieving the effects of temperature on the growth of sea cucumbers. The experiments were studied to compare the recirculating aquaculture with static aquaculture in summer, in which the temperature was 14-16 ℃ and over 18 ℃ respectively. The results showed that the growth rate of RAS was 0.13% per day by controlling the temperature, which was distinctively higher than the static aquaculture, the removal rate of nitrite nitrogen reached 30.7% and the removal rate of ammonia nitrogen reached 44.2%. Therefore, the water quality was improved.The quality of fodder is an important factor to the growth rate of sea cucumbers. The fodders in this research were fermented by inoculating 5% of two kinds of probiotics respectively, and their main components were both kelp residue. The temperature was kept at 33 ±1 ℃ by the water bath, the water content of fermentation was raised up to 59%, p H was lower than 6.5, and the fermentation time was shortened to 5 days. The results showed that both kinds of fermentation baits could improve the food intake of sea cucumbers and purify water.The effects of different water exchange rates on the growth of sea cucumbers have been studied. The water exchange rates of the rearing tanks were 0, 10%, 20%, 30% and 100% respectively, the sea cucumbers were fed by fermentation fodder, the initial density was 3.28 kg · m-3, the culture time was 21 days. The results demonstrated that water exchange rates of 10% and 20% could get growth rates of 1.33% and 1.41% per day, and the growth rates were distinctively higher than the growth rates of other water exchange rates. The water exchange rates were proportional to the water quality. Taking the cost of changing water into account, 15% was chosen as the reference water exchange rate.The effects of different densities on the growth of sea cucumbers have been studied. The culture densities were 3.64 kg·m-3, 2.81 kg·m-3, 1.76 kg·m-3 and 0.98 kg·m-3 respectively, the sea cucumbers were fed by fermentation fodder every day, the water was changed once every day, and the culture time was 28 days. The results showed that the densities were negatively correlated with the growth rates. The growth rate was 0.56% per day under the density of 2.81 kg·m-3, and sea cucumbers grew well, the water quality was good. Taking economic benefits of aquaculture into account, 2.81 kg·m-3 was selected as the reference density. |
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