摄食配合饲料的鱼密度和EM菌对蚌鱼综合养殖系统中浮游植物的影响

通过93 d围隔实验比较了增加摄食配合饲料的鱼(草鱼和银鲫)密度和添加EM菌对三角帆蚌、草鱼、银鲫、鲢和鳙综合养殖系统中浮游植物群落和初级生产力的影响。采用2×2实验设计,设4个处理:LF0(20尾草鱼+10尾银鲫)、LFA(20尾草鱼+10尾银鲫+EM菌)、HF0(40尾草鱼+20尾银鲫)和HFA(40尾草鱼+20尾银鲫+EM菌)。所有处理中三角帆蚌、鲢和鳙密度相同,均为每个围隔内40只蚌、8尾鲢和2尾鳙。实验期间围隔内不换水,每天分2次投喂配合饲料;定期向LFA和HFA围隔内泼洒EM菌。结果显示,围隔内出现浮游植物超过81种,分别隶属7门、32科、73属;实验前期浮游植物优势种为微囊藻和栅藻,后期转为微囊藻、平裂藻和腔球藻;浮游植物生物量平均为3.2×108～8.3×108个/L;摄食配合饲料的鱼密度和EM菌对浮游植物种类组成和多样性无显著影响,但高密度草鱼和银鲫组(HF0和HFA)中浮游植物生物量和群落呼吸强度较高,初级生产力较低;添加EM菌可降低蓝藻在浮游植物生物量中的比例,增加初级生产力。研究表明,在蚌鱼综合养殖中放养摄食配合饲料的鱼密度不宜过高。

Effects of stocking density of the fishes fed formulated feed and EM product on phytoplankton community in a mussel-fish integrated system

Integrated culture of pearl mussel Hyriopsis cumingii and planktivorous fishes, such as Hypophthalmichthys molitrix and Aristichthys nobilis is widely used in commercial freshwater pearl mussel farming. Previous studies reported that stocking Ctenopharyngodon idella and Carassius auratus gibelio in an integrated system comprising H. cumingii, H. molitrix and A. nobilis and feeding C. idella and C. auratus gibelio with formulated feed could increase pearl production and mussel growth. At present, the integrated system of pearl mussel, C. idella, C. auratus gibelio, H. molitrix and A. nobilis has been widely used as a model for freshwater H. cumingii farming. However, the suitable stocking density of C. idella and C. auratus gibelio remains to be determined. Generally, increasing density of the fishes fed with formulated feed can increase either fish production or waste output, and the increased accumulation of toxic inorganic nitrogen (ammonia and nitrite) and organic matters can negatively affect health and growth of the farmed H. cumingii and fishes. Although microbial products have been recognized as a potential technique to alleviate the environmental impact and enhance the production performance in aquaculture practices, knowledge about application of microbial products in Hyriopsis cumingii farming is scarce. In the present study, a 93-day experiment was conducted in land-based enclosures to evaluate the effect of stocking density of the fishes (C. idella and C. auratus gibelio) fed with formulated feed and effective microorganisms (EM) on structure and function of phytoplankton community in an integrated system of H. cumingii, C. idella, C. auratus gibelio, H. molitrix and A. nobilis. Four treatments abbreviated as LF0 (20 C. idella + 10 C. auratus gibelio + 40 mussel + 8 H. molitrix + 2 A. nobilis), LFA (20 C. idella + 10 C. auratus gibelio + 40 mussel + 8 H. molitrix + 2 A. nobilis + EM supplementation), HF0 (40 C. idella + 20 C. auratus gibelio + 40 mussel + 8 H. molitrix + 2 A. nobilis), and HFA (40 C. idella + 20 C. auratus gibelio + 40 mussel + 8 H. molitrix + 2 A. nobilis + EM supplementation) were established. The pearl mussel included 20 grafted mussel and 20 non-grafted mussel. Each treatment was three replicated, and total 12 enclosures were used. During the experiment, species and biomass of phytoplankton were monitored at the intervals of four weeks, and chlorophyll a (Chl.a) and primary productivity were measured at the intervals of two weeks. Results showed that more than 81 phytoplankton species that belonged to 7 phyla, 32 families and 73 genera were identified. Microcyslis sp. and Scenedesmus sp. dominated in phytoplankton community at the early stage of the experiment, and Microcyslis sp., Merismopedia sp. and Coelosphaerium sp. dominated at the later stage. The phytoplankton biomass ranged from 3.2×10⁸ to 38.3×10⁸ cells/L. No significant differences were found in the species composition of phytoplankton among treatments LF0, LFA, HF0 and HFA. The increase of stocking density of C. idella and C. auratus gibelio resulted in the increase of phytoplankton biomass and community respiration and the decline of the primary productivity. EM supplementation did not significantly affect species composition and diversity of phytoplankton, but resulted in the decrease of the ratio of blue-green algae to phytoplankton biomass and the increase of the primary productivity. This study reveals that the fishes (C. idella and C. auratus gibelio) fed with formulated feed should not be stocked at high densities in the mussel-fish integrated system.