A.繼發(fā)性感染B.主動(dòng)經(jīng)皮感染C.被動(dòng)經(jīng)皮感染D.混合感染
A.2mg/LB.4mg/LC.8mg/LD.20mg/L
A.徹底清池B.投喂優(yōu)質(zhì)餌料C.換水D.合理放養(yǎng)