海水实验围隔中放养罗非鱼的生态学效应

Ecological effects of tilapia stocked in seawater experimental enclosures

围隔实验和在围隔内进行的其他实验结果表明，台湾红罗非鱼（简称罗非 鱼）对食物的选择性及其生态学效应与食物资源状况有关．放养罗非鱼的围隔中浮 游植物生物量和生产力往往较高，但罗非鱼密度超过８ ０００尾／ｈｍ2 后可明显压制海 洋原甲藻等大型鞭毛藻类．当罗非鱼食物丰富时其对围隔中桡足类的压制作用相对 较弱，当其他食物资源缺乏时往往选择捕食个体较大的桡足类。放养罗非鱼对围隔 水中氮浓度和ＣＯＤ的影响较小，但加快了磷的循环，罗非鱼密度超过８ ０００尾／ｈｍ２ 的围隔中 ＰＯ４－ Ｐ浓度明显高于对照围隔。

The results of enclosure experiment and other in situ ecological experiments, which were carried out between 20 August and 16 September 1996, show that food selection of hybrid tilapia, Oreochromis mossambicus× O. niloticus, and its ecological effects are dependent on food resources available in enclosures. Biomass and production of phytoplankton in the enclosures that stocked tilapia are usually higher than the control enclosure. However, flagellate algae such as Prorocentrum micans, is difficult to be dominant species when more than 8000 tilapia per hm2 is stocked. Tilapia do not exhibit significant impacts on copepods when their preferable food is abundant, but selectively capture copepods of large body size when other food resources are scarce. Concentrations of nitrite, nitrate, ammonia and total nitrogen, and chemical oxygen demand are not significant different between the enclosures stocked tilapia and the control enclosure. Concentration of reactive phosphate in the enclosures that stocked tilapia with densities of more than 8 000 fish per hm2, is relatively high because of improved phosphorus cycle.