Short communication Metabolite and gene expression responses in juvenile flounder Paralichthys olivaceus exposed to reduced salinities Huifeng Wu a, * , Jialin Liu a, b , Zhen Lu a, b , Lanlan Xu a, b , Chenglong Ji a , Qing Wang a , Jianmin Zhao a a Key Laboratory of Coastal Zone Environmental Processes, Yantai Institute of Coastal Zone Research (YIC), Chinese Academy of Sciences (CAS), Shandong Provincial Key Laboratory of Coastal Zone Environmental Processes, YICCAS, Yantai 264003, PR China b University of Chinese Academy of Sciences, Beijing 100049, PR China article info Article history: Received 14 December 2016 Received in revised form 23 February 2017 Accepted 24 February 2017 Available online 27 February 2017 Keywords: Salinity Biological effects Paralichthys olivaceus Metabolite Gene expression abstract Seawater salinity is one of the most important changeable environmental factors influencing the behavior, survival, growth and production of marine organisms. In this work, metabolite and gene expression profiles were used to elucidate the biological effects of reduced salinities in juvenile flounder Paralichthys olivaceus. Metabolic profiling indicated that both reduced salinities (23.3‰ and 15.6‰) enhanced proteolysis and disturbed osmotic regulation and energy metabolism in juvenile flounder P. olivaceus. Furthermore, the low salinity (15.6‰) enhanced anaerobic metabolism indicated by the elevated lactate in flounder tissue extracts. Gene expression profiles exhibited that reduced salinities could induce immune stress and oxidative stress and disturb energy metabolism in juvenile flounder P. olivaceus. In addition, reduced salinities might promote the growth and gonadal differentiation in juvenile flounder P. olivaceus. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction The marine environmental factors, such as salinity, temperature, hypoxia, photoperiod and so on, may impact on the physiological and biological status of marine animals in a wide variety of ways [1]. Natural changes in seawater salinity occur frequently due to rainwater diluting seawater or mixing of estuarine waters. Evi- dences have indicated that salinity changes can effectively affect different processes in marine animals [1]. Li et al. reported the significant up-regulation of heat shock proteins induced by the low salinity, which suggested that low salinity influenced the innate immunity in pearl oysters Pinctada martensii [2]. In marine fishes, most studies focused on the effects in osmoregulation, immune system and energy metabolism induced by salinity changes [1,3,4]. For example, Cuesta et al. have found that salinity influences the humoral immune parameters of gilthead seabream (Sparus aurata L.) [5]. Olive flounder Paralichthys olivaceus is an economically impor- tant fish species in marine aquaculture industry in China. It widely distributes in open seas with high salinities and estuaries with low salinities, suffering dramatic salinity alterations [6]. The early life stages of P. olivaceus, larva and juvenile, can survive in a salinity with a range from 5‰ to 45‰ [6]. Previously, researchers mainly tested the physiological parameters to characterize the effects of salinity in P. olivaceus at early life stages. Tang et al. studied the effects of low salinity stress on the growth of juvenile fish P. olivaceus [7]. They demonstrated that the low salinity (5‰) could significantly decrease the growth rate of juvenile P. olivaceus stressed by this salinity for 1 week [7]. However, a medium salinity (16‰) may increase the growth rate and decrease the albinism rate of both larval and juvenile fish P. olivaceus [6]. Recently, the biochemical indices have been measured to interpret salinity- induced effects and mechanisms in juvenile P. olivaceus [8]. Basi- cally, low salinity (10‰) may increase the activities of superoxide dismutase (SOD) and catalase (CAT) in juvenile P. olivaceus, which suggested that low salinity could induce oxidative stress in juvenile P. olivaceus [8]. In addition, low salinity (5‰) can influence the plasma osmolality in gills of juvenile P. olivaceus by decreasing the activity of Na þ -K þ -ATPase [8]. However, there is a lack of knowl- edge related to salinity-induced effects in P. olivaceus at molecular levels. With the development of -omic techniques, including genomics, * Corresponding author. E-mail address: hfwu@yic.ac.cn (H. Wu). Contents lists available at ScienceDirect Fish & Shellfish Immunology journal homepage: www.elsevier.com/locate/fsi http://dx.doi.org/10.1016/j.fsi.2017.02.042 1050-4648/© 2017 Elsevier Ltd. All rights reserved. Fish & Shellfish Immunology 63 (2017) 417e423