刺参苗期附着基更换频率对刺参生长及其养殖系统菌群结构的影响

为了探究刺参(Apoasichopus japonicus)保苗阶段(7–9月)最佳的附着基更换频率(changing frequency,CF),本实验在夏季保苗期设置5个附着基更换频率组,即CF10、CF20、CF_(30)、CF40和CF_(50)。采用实验生态学的方法,并结合传统细菌培养法和16S r DNA细菌鉴定技术对上述不同实验组进行检测。结果表明:CF20组刺参整池增重和个体增重幅度最大,CF_(30)次之,CF_(50)组由于死亡率高,整池重量为负增长。CF20组的特定生长率和存活率分别为(5.986±0.135)%/d和(95.231±0.265)/%,且显著高于其他各组(P0.05),CF_(30)次之,而CF_(50)组的特定生长率和存活率最低,且显著低于其他各组(P0.05)。养殖用水中4NH+-N、2NO--N和COD随着附着基更换频率的降低而升高,并在第50天时分别达到0.53 mg/L、0.28 mg/L、0.18 mg/L。各实验组水体中异养细菌和弧菌数量随附着基更换频率变化不明显,而附着基上的异养细菌和弧菌数量随附着基更换频率的降低而升高,CF_(50)组异养细菌总数在第50天时达到1.38×105 cfu/cm2,弧菌数量达到1.5×104 cfu/cm2,皆明显高于其他各组。附着基上优势菌为溶藻弧菌(Vibrio algindyticus)、需钠弧菌(V.natriegens)、马胃葡萄球菌(Staphylococcus equorum)、枯草芽孢杆菌(Bacillus subtilis)、苏云金芽孢杆菌(B.thuringiensis)和副溶血弧菌(V.parahaemolyticus)。其中,溶藻弧菌为刺参条件致病菌,且一直存在于养殖系统中并逐步占据绝对优势。这与CF_(50)组在实验进行到43 d时开始出现化皮,50 d时开始出现死亡现象有一定的关系。同时,附着基长时间未更换,会滋生大量玻璃海鞘、日本毛壶、内刺盘管虫等敌害生物,争夺栖息空间和食物,导致刺参苗种生长减慢。综上,由实验结果显示,在7–9月高温季节每20 d更换一次附着基最佳。考虑到生产成本,附着基更换频率一般为20~30 d为宜。本研究结果为刺参苗种培育工艺的优化及刺参健康养殖提供了理论依据和参考。

Effects of substrate change frequency on growth and variation of the microflora structure in a seedling cultivation system of sea cucumber Apostichopus japonicus

To determine the best change frequency of substrates in the sea cucumber seedling cultivation system in summer, the relationship between the substrate change frequency and growth of sea cucumbers, and the microflora structure on the substrate, was investigated using an experimental ecology method, a traditional bacterial culture method and 16S rDNA sequence analysis. Five different substrate change frequency groups (10 d, 20 d, 30 d, 40 d, 50 d) were set and termed CF10, CF20, CF30, CF40 and CF50. Judged by the weight gain of the whole cultivation tank and the main body weight, the group achieved the best growth rate, followed by the CF30 group. The CF50 group achieved the highest death rate, which caused a decrease in the weight of the whole tank. The specific growth rate and the survival rate of the CF20group were (5.986±0.135)%/d and (95.231±0.265)%, respectively, which were significantly higher than the other groups (P<0.05). The concentration of ammonia nitrogen (4NH+-N), nitrite (2NO--N) and chemical oxygen demand (COD) of the pond water increased along with the decrease in the change frequency of substrates, reaching 0.53 mg/L, 0.28 mg/L and 0.18 mg/L on the 50th day, respectively. In terms of the concentrations of heterotrophic bacteria and vi-brios in the pond water and on the substrate, the concentrations of heterotrophic bacteria and vibrios in the pond water did not change significantly with the change frequency of substrates; however, the concentrations of heterotrophic bac-teria and vibrios on the substrate increased with decreasing change frequency of substrates, reaching 1.38×105 cfu/cm2 and 1.5×104 cfu/cm2on the 50th day in the CF50 group, respectively. Bacterial identification showed that the dominant bacteria on the substrates wereVibrio alginolyticus,Vibrio natriegens,Staphylococcus equorum,Bacilllus subtilis,Ba-cilllus thuringiensis andVibrio parahaemolyticus, of whichV. alginolyticus was the dominant bacteria.V. alginolyticus is an etiological pathogen for A. japonicus; therefore, it might have a close relationship with the occurrence of skin ul-cerative syndrome in the CF50group. Harmful animals, such asCiona intestinalis,Grantia nipponica, andHydroides ezoensis, compete for living space and food, causing slow growth of sea cucumbers. These animals emerged when the substrates had not been changed for a long time. The above results indicated that the optimal substrate change was once every 20 d in summer (July to September). Taking the production cost in consideration, it was suggested that the sub-strate should normally be changed once between 20 d and 30 d. These results will help to optimize breeding processes and health management for sea cucumbers.