Abstract
Changes in environmental salinity challenge fish homeostasis and may affect physiological performance, such as swimming capacity and metabolism, which are important for foraging, migration, and escaping predators in the wild. The effects of salinity stress on physiological performance are largely species specific, but may also depend on intra-specific differences in physiological capabilities of sub-populations. We measured critical swimming speed (Ucrit) and metabolic rates during swimming and at rest at salinities of 0 and 10 in European perch (Perca fluviatilis) from a low salinity tolerance population (LSTP) and a high salinity tolerance population (HSTP). Ucrit of LSTP was significantly reduced at a salinity of 10 yet was unaffected by salinity change in HSTP. We did not detect a significant cost of osmoregulation, which should theoretically be apparent from the metabolic rates during swimming and at rest at a salinity of 0 compared to at a salinity of 10 (iso-osmotic). Maximum metabolic rates were also not affected by salinity, indicating a modest tradeoff between respiration and osmoregulation (osmo-respiratory compromise). Intra-specific differences in effects of salinity on physiological performance are important for fish species to maintain ecological compatibility in estuarine environments, yet render these sub-populations vulnerable to fisheries. The findings of the present study are therefore valuable knowledge in conservation and management of estuarine fish populations.
Highlights
Most aquatic species only tolerate and perform well in the stable environmental salinities of either fresh water or sea water [1,2]
Salinity change seemed to affect Ucrit more in the group of fish that started at a salinity of 10, there were no effects of COT was significantly affected by swimming speed in low salinity tolerance population (LSTP) (LMM, F1,58.668 = 13.342, p < 0.001), yet not by salinity, time, nor salinity treatment order, and there was no interaction between swimming speed and salinity
In high salinity tolerance population (HSTP), COT was significantly affected by swimming speed (LMM, F1,62.899 = 21.306, p < 0.001), but not by salinity nor salinity treatment order, and there was no interaction between swimming speed and salinity
Summary
Most aquatic species only tolerate and perform well in the stable environmental salinities of either fresh water or sea water [1,2]. Estuaries usually have high biological productivity due to nutrient input from terrestrial run-off [4] and the high food availability and low inter-specific competition may be a strong driving force for physiological adaptation to tolerate and perform well at intermediate salinities [5,6]. Biology 2019, 8, 89 produce multiple phenotypes in response to different ambient environments [7], or through genetic adaptation [8,9]. Such intra-specific differences in physiological performance can be crucial for species for maintaining high fitness in novel environments [8,10].
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