鲢滤食不同藻类的磷吸收及排泄过程研究

PHOSPHORUS CYCLE OF SILVER CARP FEEDING ON DIFFERENT ALGAE AND ITS EFFECT ON THE WATER NUTRIENT CYCLE

为探究滤食性鱼类对水体营养元素地球化学循环过程的影响开展了室内实验,研究了鲢(Hypophthalmichthys molitrix)对藻类的滤食效率,测定了滤食过程中鲢对磷的吸收和排泄,并分析了排泄对水体中氮、磷的影响。结果表明:(1)鲢通过滤食作用降低了藻类密度,且对不同藻类的滤食效率无显著差异;(2)在水体中,鲢滤食藻摄入磷并排泄溶解性磷(SRP),在食物充足时可维持水体总磷(TP)相对稳定,在食物不充足时,鲢消耗自身营养并持续排泄SRP,成为新磷源;(3)鲢摄入食物后以高氮磷比(N﹕P)向环境再供应无机营养,食物中大部分氮和少部分磷以无机营养形式排泄,使滤食组水环境N﹕P显著高于control组,其中滤食蓝藻组水环境N﹕P显著高于硅藻、绿藻组,提示鲢对藻的滤食促进水体营养向磷限制转换,尤其是滤食蓝藻可能加强这种趋势。总之,鲢不仅可通过摄食压力降低藻密度,同时能以高N﹕P排泄再分配营养影响藻生长,其对水体营养循环的作用值得关注。

In order to explore the impact of filter-feeding fish on the geochemical cycle of water nutrients,an indoor experiment was conducted to study the filter-feeding efficiency of silver carp(Hypophthalmichthys molitrix)on algae,and to measure the absorption and excretion of phosphorus by silver carp during the filter-feeding process,also we analyzed the influence of excretion on nitrogen and phosphorus in water bodies.The results showed that(1)silver carp reduced the population density of cyanobacteria,green algae,and diatoms through filter feeding,with comparable effectiveness against cyanobacteria as against green algae and diatoms;(2)silver carp filter-feeds on algae by ingesting particulate phosphorus(PP)and excreting soluble phosphorus(SRP)into the water.In the presence of sufficient food supply,the total phosphorus(TP)of the water body remained relatively stable.However,when the food was insufficient,the silver carp consumed its own nutrients,continuing to release SRP into the water,contributing to phosphorus raise;(3)Following food consumption,silver carp reintroduced inorganic nutrients to the water environment,leading to a high nitrogen-to-phosphorus(N﹕P)ratio.Most nitrogen and a small part of phosphorus from the food were excreted as inorganic nutrients,resulting in significantly higher N﹕P ratios in the water environment of the filter-feeding group compared to the control group.Furthermore,the N﹕P ratio in the water environment of the filter-feeding cyanobacteria group was significantly higher than that of the diatom and green algae groups,suggesting that silver carp’s filter feeding on algae promotes the shift toward phosphorus limitation in the water body,and in particular,filter feeding cyanobacteria may strengthen this trend.In conclusion,silver carp might not only reduce the density of algae through feeding pressure but also affect the growth of algae with high N﹕P excretion and redistribution of nutrients.The role of silver carp in the nutrient cycle of water body deserves more attention.