硝氮胁迫对不同沉水植物生理生长的影响

沉水植物是水生生态系统的初级生产者，对调控生态系统能量的循环和传递，维持水生态系统的结构和功能。都有极为重要的作用。为了解硝态氮浓度对不同种类沉水植物生理生长的综合影响，实验采用6种浓度的硝态氮对苦草和黑藻进行胁迫处理，在实验开始后的6、24h测定植株抗氧化物酶（SOD、POD、CAT）的活性;并于实验处理7d后考察植株的叶绿素含量和各项生长指标。结果表明，缺氮条件下苦草和黑藻的SOD、POD反应强烈，40mg／L下苦草和黑藻的SOD、CAT酶活性几乎无变化；从处理时间上看，苦草总体表现为各浓度处理的SOD、CAT随胁迫时间增加活性上升，POD活性下降;黑藻生理活性表现则相反。胁迫处理7d后，苦草5mg／L处理下生物量积累最大，1～20mg／L内黑藻生物量积累没有差异，苦草的叶绿素、鲜重增量生长指标总体远低于黑藻。研究表明，10mg／L是苦草能够耐受的最高硝态氮浓度．黑藻在1～20mg／L内均能较好生长；黑藻较苦草对硝态氮胁迫具有更大的耐受性。

Comparative Study of the Growth and Gonad Development of Clarias gariepinus （Burchell 1822） Fed Diets with Plant and Animal-based Ingredients in Concrete Tanks

A twelve week experiment was conducted to compare the effects of diets with plant-based and animal-based ingredients on growth and gonad development of Clarias gariepinus. One hundred and 12 sub-adult C. gariepinus with an average weight of 205 ×5.09 g, were stocked in six concrete tanks （9 × 4 × 2 m3） containing 20 fish each. Experiment had 3 replicates and animals fed daily at 5% body weights. There was no significant difference （P 〈 0.05） in proximate compositions of the two experimental feeds and controls. Fecundity, gonad weight and gonasomatic index were higher in fish fed diet 13 than A and C. Similarly, growth indices were higher in fish fed diet B than in A and C. Histology of gonads showed a faster development of oocytes of eggs in fish fed animal-based ingredients than plant-based and combined plant and animal diets. Although there were slight differences in growth parameters and gonad development in favor of feed with animal-based ingredients, plant-based feed compared favorably in the growth and gonad development of C. gariepinus. Plant-based ingredients are recommended on the basis of affordability and availability as substitute for animal-based ingredients in C. gariepinus feed.