输入碳氮比对凡纳滨对虾生长和养殖水体水质的影响

调节碳氮比改善水质和促进对虾生长已有一些报道, 但不同实验室得出的结论经常相互矛盾. 本研究通过建立规范一致的对虾养殖实验体系, 设置对照组(CN6组, 碳氮比为6)和处理组(CN10组和CN20组, 碳氮比分别为10和20), 每组设置8个重复, 研究输入碳氮比对凡纳滨对虾生长和养殖水体水质的影响. 结果表明, 适当提高输入碳氮比可促进对虾生长和存活. 与对照组相比, CN10组的末均重、虾长、特定生长率、存活率和产量分别提高了18.04%、7.45%、13.11%、46.73%和73.03%, 而饲料转化率降低了43.41%. 此外, CN10组的水体理化指标如pH、溶解氧、氨氮、亚硝氮、磷酸盐、总磷的浓度也极显著低于CN6组. 相关性分析表明影响对虾生长的主要环境因子是亚硝氮、磷酸盐、总磷和pH. 然而, 实验第25d, CN20组对虾大量死亡, 产量和存活率都很低, CN20和CN10组的对虾体重和体长均高于CN6组, 说明过高的输入碳氮比可以促进对虾生长但不利于对虾存活. 本研究说明重复数对于实验结论的可靠性有较大影响.

Effect of input C/N ratio on Litopenaeus vannamei growth and culture water quality

The effects of C/N ratio on water quality and shrimp growth have been reported in the literature, despite of the inconsistent evidence. It might be due to the insufficient number of replicates within group, which fails to reach statistical significance. Here, eight replicates were used in the current study, in order to identify the effect of carbon supplementation on shrimp growth and water quality. Organic carbon in the form of glucose was added daily to provide calculated carbon to nitrogen (C/N) ratios of 10:1 (CN10) and 20:1 (CN20) respectively, based on the carbon–nitrogen content of the feed. No glucose was added in the control group which had a C/N ratio of 6 (CN6). The results showed that carbon supplement significantly improved shrimp growth and water quality. Compared with the CN6 group, the weight and length special growth rate, survival rate, and yield of individual shrimp were 18.04%, 7.45%, 13.11%, 46.73% and 73.03% higher, respectively. In contrast, the feed conversion rate was 43.41% lower in the CN10 group than that in the CN6 group. In addition, the water quality parameters (pH, dissolved oxygen, ammonium, nitrite, phosphate and total phosphate) concentration of the CN10 group was significantly lower than that of the group CN6. Water pH, ammonium, nitrite, and total phosphate concentration were the main factors regulating the shrimp survival in group CN6 and CN10. However, mass shrimp mortality was observed in the CN20 group at day 25. These results suggested that excessive carbon supplement may be beneficial to shrimp growth, but result in higher mortality. Further studies are needed to indentify the impact of C/N ratio on shrimp culture systems.