氨氮对凡纳对虾免疫指标的影响

Effects of ammonia-N on immune parameters of white shrimp Litopenaeus vannamei

以凡纳对虾(Litopenaeus vannamei)为研究对象,研究氨氮对其免疫指标的影响。实验氨氮质量浓度梯度设置为0.05(对照)、0.5、1.0、1.5、2.0、2.5 mg／L,各氨氮梯度用4g／L的氯化铵溶液来调节。将暂养在自然海水(对照)中的凡纳对虾分别放入各实验梯度中,对虾体长为(8.5±0.5)cm。结果表明,氨氮对凡纳对虾血细胞数量、血清中的酚氧化酶活力、溶菌和抗菌活力的影响显著(F>F0.05),且随着氨氮质量浓度的升高,血细胞数量和溶菌、抗菌活力降低,酚氧化酶活力升高;在0-24 h实验时间内,各处理组(对照组除外)对虾血细胞数量和溶菌、抗菌活力呈下降趋势,酚氧化酶活力呈上升趋势,24 h后稳定在较低水平上。实验说明,随着氨氮水平升高,凡纳对虾免疫力明显下降,对病原菌的易感性提高,因此在养殖过程中,环境氨氮变化幅度不应超过0.5 mg／L,或长时间维持在较高氨氮水平(>0.5 mg／L)。

An important environmental concern associated with intensive shrimp culture is the production of ammonia, which is formed through ammonification of organic matter like unconsumed food and feces. Dur-ing the shrimp culture processes, the level of ammonia in water will increase suddenly for the death of the dominant population of phytoplankton and the accumulation of unconsumed food and feces. High levels of ammonia can affect the survival and growth,respiration,hemolymph osmotic pressure in shrimp, and even cause mortality.Effect of ammonia has been reported to reduce total haemocyte count(THC) of crustaceans and lead to an enhanced sensitivity to pathogens. This paper studies effect of ammonia on immune parame-ters of Litopenaeus vannamei,analyzes the changes of different immune parameters under different ammonia levels within 48 h, and aims to discuss the mechanism of the shrimp immunological regulation and also provids a scientific basis for water quality regulation in shrimp culture.Adults L. vannamei were obtained from commercial farms in Yinghai and Qingdao. The body length of healthy shrimp is(8.5±0.5) cm, with no significant difference among various treatments. These shrimps were acclimated in tanks (30 cm × 40 cm × 50 cm) containing aerated water (salinity 30, pH 8.0) with an air-lift for 8 to 10 d prior to experimentation in the laboratory at (23 ±0.5) ℃. The water in each tank was re-newed twice daily by 1/2 volume. During the acclimation period,the shrimps were fed a formulated shrimp diet daily.Before experiment the shrimp were stopped to feed for 48 h.Six ammonia-N Ievels of 0.05(the control) ,0.5,1.0,1.5,2.0 and 2.5 mg· L-1 were designed using ammonium chloride solution of 4 g· L-1 to adjust. During the experiment, ammonia Ievels were measured every 4 h and varied at(0.12 ± 0.05), (0.53±0.02),(1.08±0.10),(1.48±0.05),(2.06±0.07) and (2.58±0.04) mg/L,respectively,and no shrimps died.For each treatment, there were three triplicate groups. Three shrimps were sampled ran-domly from each group at the time intervals of 0, 4, 8, 12, 24 and 48 h, respectively.The results indicate that ammonia-N has significant effects on THC,phenoloxidase, bacteriolytic and antibacterial activities in haemolymph ( F > F0.05) of shrimp. As ammonia-N concentration increases, the Ievels of THC, bacteriolytic and antibacterial activities decrease, while the phenoloxidase activity increases gradually. As the time of sampling increases,the Ievels of THC,bacteriolytic and antibacterial activities decrease, while the phenoloxidase activity in the haemolymph increases gradually in all groups except the control. All the immune parameters remain at a constant Ievel after 24 h. It is considered that after the increase of ammonia Ievels, the emergency reaction lead to decompensation and decrease of immune capacity and increase of sensitivity to pathogen in shrimps. Therefore, during L. vannamei culture periods it is necessary to take useful measures to reduce ammonia Ievels if ammonia-N concentration excesses 0.5 mg·L-1.