两种营养源对主养草鱼池塘浮游生物群落结构与碳/氮转化的影响

摘要

为探讨主养草鱼池塘主要生源要素的营养循环过程与能量转化效率,本实验运用稳定同位素(δ13C、δ15N)与C/N分析技术,研究两种不同投喂营养源(苏丹草、人工饲料)对主养草鱼池塘浮游生物群落结构、C-N营养转化可能存在的影响.结果显示,两种投喂营养源对浮游生物的群落结构没有显著的影响,但投喂苏丹草更有利于浮游生物的群落增长.在投喂苏丹草的池塘,绝大部分苏丹草的能量被草鱼、团头鲂所利用(84%),而鲢、鳙利用较少(6.8%).苏丹草对水体中颗粒有机物(POM)贡献了7.4%的能量.在投喂人工饲料的池塘,70.9%的人工饲料能量被草鱼和团头鲂利用.由于人工饲料的颗粒性特征,有少量饲料形成的碎屑被鳙利用(5.1%),另有8.1%和12%的能量分别贡献于POM和沉积物.研究表明,两种饲料源的营养元素首先被草食性鱼类利用,其次通过水体中浮游生物以及残饵、鱼类粪便传递给滤食性鱼类,最后归于沉积物.与人工饲料相比,苏丹草的营养元素更多被鱼类利用,较少浪费于沉积物中,其传递到沉积物的过程较慢.鱼类的能量转化与投喂的饵料密切相关,投喂苏丹草池塘的鱼类能量转化效率要高于投喂人工饲料的池塘.%To figure out the nutrient cycling process and energy conversion efficiency of major biogenic elements in grass carp (Ctenopharyngodon idella) poly-culture ponds, this study investigated the potential effects of two different foodstuff sources (Sudan grass S. Sudanense, and formula feed) on the plankton community structure, and C/N trophic shift in grass carp poly-culture ponds using analytical techniques of stable isotope (δ13C and δ15N) and C/N ratio. Our results showed that two feeding modes yielded no statistically significant impact on the community structure of plankton, but the feeding mode with Sudan grass helped promote the plankton growth in the water column. In the ponds fed with Sudan grass, Sudan grass contributed 84% and 6.8% of energy to herbivorous and filter-feeding fishes (silver carp H. michthysmolitrix and bighead carp A. nobilis)), respectively. Moreover, Sudan grass contributed 7.4% of energy to particulate organic matter. In the ponds fed with artificial feed, herbivorous fish derived 70.4% of energy source from formula feed. Formula feed contributed 5.1%, 8.1% and 12% of energy source to bighead carp, POM and sediment, respectively. Our findings suggested that, first of all, the carbon and nitrogen elements of two foodstuff sources were utilized by herbivorous fish (grass carp and blunt-snout bream M. amblycephala), and then transferred the nutrients to filter-feeding fishes through the pathways of plankton, residual feeds and fish feces. Ultimately, the biogenic elements were dedicated to the sediment. In contrast with formula feed, the nutrient of Sudan grass could be more utilized by cultured fish than that deposited in the sediment. The trophic transfer was slower in ponds fed by Sudan grass than that in ponds fed by formula feed. Energy transfer of cultured fish was extremely relevant to foodstuff sources. In particular, the conversion efficiency in Sudan grass ponds was higher than that in formula feed ponds.