大薸对网箱养殖长吻鮠生长及氮、磷排放的影响

为降低网箱养鱼对水体的污染,探求环保型生态网箱,以体质量为(217.86±36.01)g的长吻鮠Leiocassis longirostris幼鱼和大薸Pistia stratiotes L为研究对象,对生态网箱与传统网箱中氮(N)、磷(P)的输入和回收情况进行了比较试验.结果表明:生态网箱和传统网箱中N的回收率分别为47.80％和44.36％,两组网箱间无显著差异(P＞0.05),生态网箱和传统网箱中P的回收率分别为35.01％和32.53％,两组网箱间差异显著(P＜0.05)；生态网箱和传统网箱中N的利用率分别为26.87％、25.37％,P的利用率分别为15.82％、15.55％,生态网箱中N、P的利用率略高于传统网箱,但两组网箱间均无显著差异(P＞0.05)；试验期间生态网箱内大薸共有3次收割,收获总质量为189.5 kg,大薸净增重为154.25 kg,对水中N、P的移除量分别为257.32 g和67.08 g.通过计算大薸对水中N、P的移除量以及网箱养殖长吻鮠N、P的输入和输出总量,从理论上得出网箱面积与大薸栽培面积比为1∶32～35时,可实现网箱养殖长吻鮠N、P的零排放.

Effects of aquatic macrophyte Pistia stratiotes L. on growth and nitrogen and phosphorus budgets in Leiocassis longirostris reared in net cages

Leiocassis longirostris with body weight of（217.86 ±36.01）g was reared in a net cage of 5.0 m×4.0 m×2.5 m without（as a control group） and with aquatic macrophyte Pistia stratiotes L.（as a treatment group） at a stocking rate of 45 individuals/m2 with tetraplication at water temperature of 24-30 ℃,pH of 6.5-7.4 and dissolved oxygen level of 5.0 mg/L for 60 days to evaluate the input and recycle of nitrogen,and phosphorus in the cage water.The results showed that the recycle rate of nitrogen was found to be 47.80% in the cage with the aquatic plant and 44.36% in the control cage,without significant difference（P0.05）.The recycle rate of phosphorus was 35.01% in the cage with the aquatic plant and 32.53% in the control cage,with significant difference（P0.05）.There were higher utilization efficiencies of nitrogen（26.87%）,and phosphorus（15.82%） in the cage with the aquatic plant than those（25.37% for nitrogen,and 15.55% for phosphorus）,without significant difference（P0.05）.A total aquatic plant of 189.5 kg（net weight gain of 154.25 kg） was harvested three times in the cage with the aquatic plant at the end of the experiment,with nitrogen elimination of 257.32 g and phosphorus elimination of 67.08 g.It is estimated that the nitrogen and phosphorus recycle utilization（that is,zero nitrogen and phosphorus effluent） can be obtained when the fish is cultured in a net cage at a ratio of net cage area to the aquatic plant area = 1∶32-35.