藻—溞系统对凡纳滨对虾养殖水体调控效果的研究

取5000 mL灭菌后的凡纳滨对虾养殖尾水于5000 mL高压灭菌的烧杯中,分为10组,分别为蛋白核小球藻组(C1)、蛋白核小球藻+大型溞组(C2)、衣藻组(C3)、衣藻+大型溞组(C4)、隐藻组(C5)、隐藻+大型溞组(C6)、蛋白核小球藻+衣藻组(C7)、蛋白核小球藻+衣藻+大型溞组(C8)、衣藻+隐藻组(C9)、衣藻+隐藻+大型溞组(C10),每个处理组设3个平行。各藻种原始藻液25 mL,接种初始密度为1×10^( 8) 个/mL,大型溞密度为1个/L。试验烧杯置于25 ℃、3000lx和14L∶10D光暗比的培养箱内常规培养。每间隔3 d的10:00测定溶液的pH、溶解氧、总氮、氨氮、硝态氮、亚硝态氮、总磷和叶绿素a等水质指标,研究不同藻—溞组合系统对凡纳滨对虾养殖水体净化效果及其生长的影响。试验结果显示,各处理组藻类及大型溞均可正常生长,且藻—溞组合系统具有较好的水质净化调控效果,尤其是蛋白核小球藻+衣藻+大型溞组,至试验结束时其硝态氮、亚硝态氮和氨氮的去除率分别为82%、77%和99%;混合藻生长速度要低于单一藻培养,其中蛋白核小球藻组和衣藻组微藻的相对生长速率最高,分别为27.7%和26.9%;且蛋白核小球藻最有利于大型溞的生长繁殖,至试验结束时由5个增至88个,其次是衣藻,增至80个,而隐藻最差,仅增至59个。培养初期,大型溞的扰动作用能够促进藻类的生长,随着大型溞数量的增多,大型溞的牧食压力能够阻止藻密度过密,从而能够长久维持有益藻相的稳定。在本试验研究条件下,接种蛋白核小球藻、衣藻以及大型溞最适于养殖水环境调控,维持藻相稳定。

Effects of Algae-Daphnia Systems on Regulation of Effluent from Pacific White Shrimp Litopenaeus vannamei Culture and Growth of Microalgae and Water Fleas Daphnia magna

A total of 5000 mL of sterilized water in Pacific white shrimp Litopenaeus vannamei rearing ponds was held in a 5000 mL autoclaved beaker, divided into 10 groups, and inoculated with various combinations of algae and water fleas Daphnia magna with initial alga inoculation density of 1×10 ⁸ cell/mL and water fleas density of 1 individual/L , namely, Chlorella pyrenoidosa group (C1), C. pyrenoidosa + D. magna group (C2), Chlamydomonas sp. group (C3), Chlamydomonas sp. + D. magna group (C4), Cryptomonas obovat group (C5), C. obovat + D. magna group (C6), C. pyrenoidosa + Chlamydomonas sp. group (C7), C. pyrenoidosa + Chlamydomonas sp. + D. magna group (C8), Chlamydomonas sp. + C. obovat group (C9), and Chlamydomonas sp. + C. obovat + D. magna group (C10), with 3 parallel groups. The pH value, and contents of dissolved oxygen (DO), total nitrogen (TN), ammonia nitrogen, nitrate nitrogen, nitrite nitrogen, total phosphorus (TP) and chlorophyll a were measured every 3 days to investigate the effect of the combined system on the purification of the water in Pacific white shrimp culture and growth of both the shrimp and the algae. It was found that both microalgae and D. magna grew normally in the treatment groups, with good water purification effect of the alga-water fleas combination system, and in particular, the removal rates of 82% for nitrate, 77% for nitrite and 99% for ammonia nitrogen at the end of the experiment. There was poor growth rate in polycultured microalgae than that in monoculture microalgae, with the maximal relative growth rates of 27.7% in C. pyrenoidosa and 26.9% in Chlamydomonas sp.. C. pyrenoidosa was the most favorable for the growth and reproduction of D. magna which was increased from 5 to 88 in number at the end of the experiment, followed by Chlamydomonas sp. (80) and C. obovata (59). In the early stage of culture, D. magna promoted the growth of microalgae, and later prevented the excessive propagation of microalgae, so as to maintain the stability of beneficial algae phase for a long time due to the increase in number of water fleas feeding pressure. Thus, inoculation of C. pyrenoidosa , Chlamydomonas sp. and D. magna were beneficial to the regulation of aquaculture water environment and to maintain the stability of microalgae phase.