Differential Coping Strategies in Response to Salinity Challenge in Olive Flounder

Abstract

To examine how different fish coping strategies respond to salinity challenge, olive flounder (Paralichthys olivaceus) with active coping style (AC) and passive coping style (PC) were transferred from seawater (SW) to freshwater (FW) and their behavior and physiology were analyzed. Different behavioral coping strategies, in terms of escape and feeding tendencies, were confirmed in AC and PC fish without FW exposure. Differences in swimming distance between AC and PC flounder were then assessed after 1 and 2 days of FW transfer. Plasma parameters and branchial gene expression were also determined 2, 5, 8, and 14 days after transfer, with comparisons between AC and PC fish and against a SW-acclimated control group. The results showed that: (1) PC flounder exhibited a significant reduction in swimming activity, while AC flounder significantly increased locomotion 2 days after transfer. (2) The plasma osmolality and plasma ionic (Na+ and Cl−) concentration of FW-acclimated PC flounder declined in a continuous fashion over time but this contrasted against the plasma parameters of AC flounder which fluctuated below the baseline level of a SW-acclimated control group. (3) The expression of NKA-α1 and NHE-3-like mRNA in PC flounder gill increased significantly from 5 days, but the expression of these two genes in AC flounder only increased after 8 days of transfer. (4) There were no remarkable differences observed in Rhcg expressions between AC and PC flounder. This study indicates for the first time that PC flounder adopt a “freeze-passive tolerance” strategy while AC flounder adopt a “flight-active resistance” defense strategy in response to salinity challenge.

Individuality in flounder ( Paralichthys olivaceus ): Differential responses of immune–endocrine during temperature stress in head kidney

“…Mice in the passive group had a higher number of tumour focal, higher corticosterone levels and lower NKG2D receptor expression than mice in the active group (Azpiroz et al, 2008). When studying fish, it was found that there are differences in swimming, metabolism and osmotic pressure of zebrafish or flounder with different behaviours after salinity stress, suggesting that there are differences in coping strategies between the two types of fish under salinity stress (Yuan et al, 2018; Zeng et al, 2019). This study showed that the immune system of BI did not change significantly compared with BOT during acute cold stress, but the immune system of SI changed significantly compared with SOT.…”

“…Intraspecific individual differences are a common phenomenon in the animal kingdom. Many research results show that the stable individual differences in animals are closely related to their life‐history strategies (Long et al, 2021; Yuan et al, 2017; Zeng et al, 2019; Zou et al, 2019). This kind of stable behavioural difference between individuals is what researchers call ‘individuality’ in animals (Long et al, 2021).…”

“…Behavioural and physical characteristics are often used to describe individuality (e.g., bold and shy) performance (Rupia et al, 2016). The difference in behaviour between bold individuals (BI) and shy individuals (SI) is most evident in the fact that BI has a higher feeding tendency and social status than SI and is more active in exploring new environments (Zeng et al, 2019). Current research shows that there are also differences in the physiological characteristics of two individuality types of fish.…”

“…Under stress, BI adopts an active, evasive coping strategy associated with an increase in metabolic rate, whereas SI resists stress by decreasing movement and respiratory metabolism (Rupia et al, 2016). The plasma osmotic pressure and plasma ion concentration of BI and SI had different changes under salinity stress (Zeng et al, 2019). In addition, studies have shown that UII (Urotensin II), UI (Urotensin I) and CRH (corticotropin‐releasing hormone) influence animal behaviour (do Rego et al, 2008; Le Mével et al, 2008; Lu et al, 2019; Paretkar & Dimitrov, 2018).…”

A World for Reactive Phenotypes

“…For instance, bold crabs were the first to disperse when habitat quality was reduced (Belgrad and Griffen, 2018). Bolder fish make more attempts to escape laboratoryinduced hypoxia (Brelin et al, 2005;Ferrari et al, 2016), salinity challenges (Zeng et al, 2019) or high ammonia concentrations (Gesto et al, 2020). Bold individuals are also better at avoiding or escaping fishing gear (Diaz Pauli and Sih, 2017).…”