Histological and transcriptomic responses of two immune organs, the spleen and head kidney, in Nile tilapia (Oreochromis niloticus) to long-term hypersaline stress

Chang Xu; Erchao Li; Yantong Suo; Yujie Su; Minghui Lu; Qun Zhao; Jian G Qin; Liqiao Chen

doi:10.1016/j.fsi.2018.02.041

Histological and transcriptomic responses of two immune organs, the spleen and head kidney, in Nile tilapia (Oreochromis niloticus) to long-term hypersaline stress

Fish Shellfish Immunol. 2018 May:76:48-57. doi: 10.1016/j.fsi.2018.02.041. Epub 2018 Feb 24.

Authors

Chang Xu¹, Erchao Li², Yantong Suo³, Yujie Su³, Minghui Lu⁴, Qun Zhao⁵, Jian G Qin⁶, Liqiao Chen³

Affiliations

¹ Department of Aquaculture, College of Marine Sciences, Hainan University, Haikou, Hainan 570228, China; School of Life Sciences, East China Normal University, Shanghai 200241, China.
² Department of Aquaculture, College of Marine Sciences, Hainan University, Haikou, Hainan 570228, China. Electronic address: ecli@bio.ecnu.edu.cn.
³ School of Life Sciences, East China Normal University, Shanghai 200241, China.
⁴ Hainan Dingda Aquaculture Co., Ltd., Wenchang, Hainan 571343, China.
⁵ Department of Aquaculture, College of Marine Sciences, Hainan University, Haikou, Hainan 570228, China.
⁶ School of Biological Sciences, Flinders University, Adelaide, SA 5001, Australia.

PMID: 29486352
DOI: 10.1016/j.fsi.2018.02.041

Abstract

Hyperosmotic stress can adversely affect fish immunity, but little is known about the histological and transcriptomic responses of immune organs in fish in a hyperosmotic environment. This study evaluated the effects of long-term hypersaline conditions (16‰) on the growth, histology and transcriptomics of the two main immune organs, the spleen and head kidney, in Nile tilapia Oreochromis niloticus relative to those reared in freshwater for eight weeks. No differences in weight gain and specific growth rate were found between fish reared under these two salinities. Hyperosmotic stress induced a congestive or enlarged spleen. Platelet- and coagulation-related gene expression was significantly decreased in tilapia at 16‰. The red cell distribution width and value of the mean corpuscular hemoglobin were significantly greater in fish at 16‰ salinity than in control fish in freshwater. A large volume of melano-macrophages in the spleen and pigment deposition in both the spleen and head kidney were observed in the histological sections in fish at 16‰ salinity. Transmission electron microscopic results showed abnormal macrophages with deposition granules in the spleen and head kidney and more neutrophils in the head kidney of fish at 16‰ than in control fish. In total, 772 and 502 genes were annotated for significantly different expression in the spleen and head kidney, respectively, and corresponded to five and one significantly changed immune system pathways, respectively. The complement pathway in the spleen was significantly down-regulated at 16‰. This study indicates that long-term exposure of Nile tilapia to a hyperosmotic environment can induce splenomegaly, reduce coagulation function, enhance phagocytic activity and down-regulate the complement pathway in the spleen. The spleen is a more sensitive organ for immune responses to chronic ambient salinity stress than the head kidney in Nile tilapia.

Keywords: Head kidney; Hematology; Immune organ; Nile tilapia Oreochromis niloticus; Phagocytosis; Spleen; Transcriptomics.

MeSH terms

Animals
Cichlids / blood
Cichlids / genetics
Cichlids / immunology*
Head Kidney / immunology*
Male
Random Allocation
Salinity*
Spleen / immunology*
Stress, Physiological / immunology
Transcriptome / immunology*