Maximum salinity tolerance and osmoregulatory capabilities of European perch Perca fluviatilis populations originating from different salinity habitats.

Emil A F Christensen,Martin Grosell,John F Steffensen

doi:10.1093/conphys/coz004

Emil A F Christensen, Martin Grosell + Show 1 more

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https://doi.org/10.1093/conphys/coz004

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Abstract

Although considered a stenohaline freshwater species, European perch (Perca fluviatilis) inhabit brackish waters. The present study determined the maximum salinity tolerance and osmoregulatory capability on individuals originating from brackish water and from freshwater populations. The fish were acclimated for 3 weeks to salinities of 0, 10, 12.5, 15, 17.5 and 20 after an initial stepwise increase to the target salinity. The maximum salinity tolerance was determined as the test salinity below which the fish could not acclimate and lost equilibrium. Blood plasma osmolality was measured if the fish had not lost equilibrium after the acclimation period. The maximum salinity tolerance was 17.5 for brackish water European perch and 10 for fresh water European perch. The high salinity tolerance of the brackish water European perch was caused by their ability to both hyper- and hypo-osmoregulate, whereas the freshwater originating fish could only hyper-osmoregulate. The results showed that maximum salinity tolerances and osmoregulatory capabilities depends on the origin habitat salinity. Due to genetic differentiation between European perch populations in brackish and fresh water, the possibility of brackish water European perch being a subspecies of European perch is discussed, yet vital knowledge concerning heritability of salinity tolerance traits is still missing. Regardless of species status, within-species plasticity in the ability to cope with varying salinities have substantial ecological and conservation implications and underlines the need for managing brackish water and freshwater European perch stocks separately.

Highlights

Environmental salinity constitutes a physiological challenge in teleosts due to osmotic water movement and ion diffusion between the environment and the internal milieu of the fish, predominantly occurring over the gills, which are permeable to facilitate respiratory gas exchange, acid-base regulation, and ammonia excretion (Evans et al, 2005)
The brackish water European perch attempted acclimated to a salinity of 20 reached loss of equilibrium (LOE) on a median time of 6 days
The blood plasma osmolality values at each treatment were The brackish water European perch had a maximum salinity tested for normality with Shapiro–Wilk’s tests, and for variance tolerance of 17.5, which was substantially higher than the maximum salinity tolerance of the freshwater European perch (10)

Summary

Introduction

Environmental salinity constitutes a physiological challenge in teleosts due to osmotic water movement and ion diffusion between the environment and the internal milieu of the fish, predominantly occurring over the gills, which are permeable to facilitate respiratory gas exchange, acid-base regulation, and ammonia excretion (Evans et al, 2005). Teleosts must keep their internal osmolalities around 300–400 mOsm kg−1 to. Osmoregulation in water above iso-osmotic level (hypo-osmoregulation) is a vastly different physiological process than hyper-osmoregulation, and is obtained by imbibing ambient water, taking up the water through the gastro-intestinal tract, and excreting excess monovalent ions through specialized branchial cells and renal excretion of divalent ions (Larsen et al, 2014)

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