低温驯化下4种不同品系罗非鱼血清皮质醇与免疫相关指标的变化

Change in serum cortisol and immune-related indices in four strains of tilapia during low-temperature acclimation

选取4种不同品系罗非鱼,分别为吉富罗非鱼(Oreochromis niloticus)、奥尼罗非鱼(O.niloticus×O.aureus)、红罗非鱼(O.nilotica♂×O.mossambica♀)和奥利亚罗非鱼(O.aureaus)。在26℃水温下饲养3周后,选取规格基本一致的罗非鱼(体质量50.73 g±4.23 g)进行低温驯化实验。水温以3℃/d的速度从26℃降至8℃,分别于水温为26℃、20℃、14℃和8℃时进行采样,比较不同驯化阶段4种不同品系罗非鱼血清皮质醇和免疫相关指标的变化规律。结果表明,与26℃时的免疫指标相比,水温降至8℃时,吉富与红罗非鱼血清皮质醇水平显著升高;然而血清C3、C4、IgM以及头肾C型溶菌酶mRNA水平显著下降(P<0.05),血清中高皮质醇水平对鱼体的免疫产生了抑制作用。水温为8℃时,奥尼罗非鱼血清皮质醇、IgM和补体C3以及头肾抗菌肽mRNA水平显著升高;奥利亚血清皮质醇、C4和IgM以及头肾C型溶菌酶mRNA水平与26℃时相比无显著差异,然而血清溶菌酶与C3水平降低。驯化实验结束后,比较了4种不同品系罗非鱼在8℃水温下48 h内的累积死亡率。吉富与红罗非鱼组累积死亡率较高,分别达到43.3%和40.0%;奥尼罗非鱼其次,为23.3%;奥利亚罗非鱼最低,为20.0%。较高的血清IgM和头肾溶菌酶和抗菌肽mRNA水平可能有助于提高奥尼和奥利亚罗非鱼的抗低温应激能力,增加低温时的成活率。本研究通过分析4种品系罗非鱼不同驯化阶段血清皮质醇和免疫相关指标,探讨不同品系罗非鱼在低温驯化过程中的免疫保护机制,旨在为下一步抗低温新品系罗非鱼的选育提供理论依据。

Low-temperature acclimation is recognized as one of the most important methods of improving cold toler-ance. The physiological response and immune function of the fish body could be changed through proper low-temperature acclimation. To elucidate the immune-protective mechanisms of various tilapia strains during low-temperature acclimation, four different strains （GIFT tilapia, hybrid tilapia, red tilapia and Aurea tilapia） were reared at 26℃. Three weeks later, individual tilapia （body weight 50.73 g ± 4.23 g） were selected and low-temperature acclimation experiments performed. Water temperature was decreased from 26 to 8℃ at a rate of 3℃/d. Blood and head kidney of three fish from each tank were sampled at 26, 20, 14 and 8℃, and the change in serum cortisol （COR） and immunity indices of the head kidney were compared in the four different tilapia strains over the course of the low-temperature acclimation. The results showed that the levels of serum COR in GIFT and red tilapia at 8℃ were significantly higher than the other strains. The levels of serum complement 3 （C3）, complement 4 （C4）, immunoglobu-lin M （IgM） and the level of c-type lysozyme mRNA in head kidney at 8℃ were significantly lower than at 26℃. COR may play an important role in the regulation of immunity activity and higher levels of COR may inhibit immunity in the fish body. Higher levels of serum COR, C4 and IgM and the expression levels of hepcidin antimicrobial peptides-1 （HAMP1） were observed at 8℃. The levels of serum COR, C4 and IgM, and expression levels of c-type lysozyme in the head kidney of Aurea tilapia were similar at water temperatures of 8 and 26℃. Lysozyme and C3 levels in serum at 8℃ were lower than at 26℃ but the expression levels of HAMP1 at 8℃ were higher than at 26℃. At the end of the low-temperature acclimation trial, cumulative mortality of the four different tilapia strains was compared at 8℃ for 48 h. Cumulative mortalities for the GIFT and red tilapia strains were 43.3%and 40.0%, respectively, and were higher than for the hybrid and Aurea tilapia strains. The cumulative mortality of Aurea tilapia was lowest （20.0%）. The higher IgM levels in serum and c-type lysozyme and HAMP1 mRNA levels in the head kidney may have enhanced the resistance of the hybrid and Aurea tilapia strains to low-temperature stress and improved survival to cold stress.