罗非鱼对微型生态系统营养物水平的影响

Effect of Nile tilapia on nutrient levels of freshwater microcosms.

本文总结了罗非鱼不同放养密度的微型生态系统中N、P浓度及P分布动态观测结果。在罗非鱼的影响下,微型生态系统中氨氮、颗粒磷和总磷浓度不同程度地高于对照组,而正磷酸盐浓度和沉积物磷的量显著地低于对照组。不同密度组某些指标的观测值虽有显著差异,但未见任何指标依罗非鱼放养密度而有规律地变动。微型生态系统中正磷酸盐浓度同浮游动、植物密度和初级生产力显著相关,氨氮浓度与浮游植物密度之间亦有显著的相关关系。然而,浮游植物密度与总磷浓度之间不存在营养级联假说所预见的下行影响,相反有前者决定于后者的上行影响的趋向。微型生态系统中P分布的变化可揭示罗非鱼促进系统中营养物循环,从而加速其富营养化的主要机制。

This paper studies the dynamics of N and P in freshwater microcosms with varying densities of Nile tilapia(Oreochromis nil(?)icus). The concentrations of ammonia (NH_3-N), particulate phosphorus (PP) and total phosphorus(TP) in microcosms with Nile tilapia are higher than those in control, but the contents of or thophosphate(PO_4-P) and sediment phosphorus are lower. There are significant differences in measured values of some indices among different density treatments, but none of these indices are found to be regularly changed with stocking density of Nile tilapia. In the microcosms, PO_4-P concentration is significantly correlated with zooplankton and phytoplankton densities and primary productivity, and NH_3-N concentration is related to phytoplankton density. The top -down effect predicted by the trophic cascade hypothesis is not existed between phytoplankton density and TP concentration, but on the contrary, there is a tendency of existing bottom-up effect. The variation of P distribution in the microcosms can reveal the main mechanism of accelerating nutrient cycling in the systems, and thus, enhancing their eutrophication processes by Nile tilapia.