盐度对莫荷罗非鱼幼鱼呼吸和氨氮排泄的影响

Effects of Salinity on Oxygen Consumption Rate and Ammonia Excretion Rate of Juvenile of Hybrid Tilapia(Oreochromis mossambicus × O. urolepis hornorum)

将莫荷罗非鱼(Oreochromis mossambicus×O.urolepis hornorum)幼鱼养殖水体盐度从淡水渐变至12、18、24、30(每天提升6)等4个目标盐度,利用间歇式呼吸仪分析幼鱼在目标盐度下5、10、15、20 d时的呼吸和氨氮排泄的变化。结果表明,在实验前期,莫荷罗非鱼幼鱼耗氧率、排氨率随盐度的升高而增加,各盐度处理组均在5 d时升到最大值,之后开始下降,下降时间、幅度与外界盐度有关。盐度12、18组幼鱼耗氧率10 d时下降至对照组水平,20 d时低于对照组水平,差异有统计学意义(P【0.05);盐度24、30组幼鱼耗氧率则在15 d时下降至对照组水平并维持稳定;幼鱼排氨率随实验时间的延长,各盐度处理组幼鱼排氨率呈先上后下降的变化,盐度24、30组幼鱼排氨率在15 d下降并维持在对照组水平,盐度12、18组幼鱼排氨率在15 d时下降至对照组水平并于20 d时低于其他盐度组,差异有统计学意义(P【0.05)。莫荷罗非鱼幼鱼适应新盐度环境后,盐度18组的耗氧率、排氨率最低,与盐度12组差异无统计学意义(P】0.05),与其他盐度处理组有差异有统计学意义(P【0.05),推测其等渗点在盐度12~18之间。不同盐度条件下,氧氮比值介于18.810~24.216间,氨熵介于0.083~0.108间,表明莫荷罗非鱼幼鱼主要依靠蛋白质和脂肪氧化供能。

The effects of salinities on the metabolic rate changes of a hybrid tilapia (Oreochromis mossambicus × O. urolepis hornorum) were investigated when salinities gradually increased with 6 every day from the fresh water to 12, 18, 24, 30 respectively. Oxygen consumption rate (RO) was measured by an intermittent flow respirometry in a controlled laboratory environment and ammonia excretion rate (RN) was determined by spectrophotometric analysis at 340 nm. The results showed that RO and RN of the hybrid tilapia increased with the rise of salinities, and increased first and then decreased with the extension of the time and got to the maximum values in each treatment at 5d, and the decline amplitudes were related with salinities. RO in salinities of 12, 18 dropped to the levels which have no significant difference with that in the control group (P>0.05) at 10 d, while significantly lower than that in the control group at 20 d (P<0.05). RO in salinities of 24, 30 decreased to the control levels and maintained stable (P>0.05) at 15 d. RN of juveniles increased with the rising salinity at 5 d and 10 d. At 15 d, RN decreased and maintained stable at the control level (P>0.05) in salinities 24 and 30. Also, in salinities 12 and 18, RN decreased to the control level at 15 d and were significantly lower than that in the other groups at 20 d (P<0.05). In the different salinities, the O:N ratio values were from 18.810 to 24.216 and ammonia quotients were from 0.083 to 0.108. It is suggested that hybrid tilapia juveniles utilize protein and lipid as main energy source, and the isotonic of hybrid tilapia will appeared when the salinity is from 12 to 18, and it is likely to be the optimal salinity for hybrid tilapia culture.