Environmental Salinity Modifies Mucus Exudation and Energy Use in European Sea Bass Juveniles.

Borja Ordóñez-Grande,Ignasi Sanahuja,Laura Fernández-Alacid,Pedro M. Guerreiro,Antoni Ibarz

doi:10.3390/ani11061580

Borja Ordóñez-Grande, Ignasi Sanahuja + Show 3 more

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https://doi.org/10.3390/ani11061580

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Abstract

Simple SummaryChanges in skin mucus production and composition offer a new means to study how fish cope with changes in the environment. We explored the utility of skin mucus as an indicator of physiological responses and energy use in a reference fish species, the European sea bass. We evaluated the exudation volume of skin mucus and the main stress- and osmoregulation-related biomarkers in both mucus and plasma. We demonstrate the viability to study the exuded volume of skin mucus composition and its parameters as an informative tool of the fish energy waste at different environmental salinities. This study is of great interest for both aquaculture and ecological studies.The European sea bass (Dicentrarchus labrax) is a euryhaline marine teleost that can often be found in brackish and freshwater or even in hypersaline environments. Here, we exposed sea bass juveniles to sustained salinity challenges for 15 days, simulating one hypoosmotic (3‰), one isosmotic (12‰) and one hyperosmotic (50‰) environment, in addition to control (35‰). We analyzed parameters of skin mucus exudation and mucus biomarkers, as a minimally invasive tool, and plasma biomarkers. Additionally, Na+/K+-ATPase activity was measured, as well as the gill mucous cell distribution, type and shape. The volume of exuded mucus increased significantly under all the salinity challenges, increasing by 130% at 50‰ condition. Significantly greater amounts of soluble protein (3.9 ± 0.6 mg at 50‰ vs. 1.1 ± 0.2 mg at 35‰, p < 0.05) and lactate (4.0 ± 1.0 µg at 50‰ vs. 1.2 ± 0.3 µg at 35‰, p < 0.05) were released, with clear energy expenditure. Gill ATPase activity was significantly higher at the extreme salinities, and the gill mucous cell distribution was rearranged, with more acid and neutral mucin mucous cells at 50‰. Skin mucus osmolality suggested an osmoregulatory function as an ion-trap layer in hypoosmotic conditions, retaining osmosis-related ions. Overall, when sea bass cope with different salinities, the hyperosmotic condition (50‰) demanded more energy than the extreme hypoosmotic condition.

Highlights

Wild European sea bass (Dicentrarchus labrax) moves seasonally from seawater to freshwater environments and vice versa, including coastal areas, lagoons, estuaries and other parts of rivers [1,2,3,4]
We compared the acclimation of European sea bass one hypoosmotic (3‰), one isosmotic (12‰)and one hyperosmotic (50‰) salinity conditions after 15 days, by measuring morphometric parameters, skin mucus and plasma stress biomarkers, and osmoregulation parameters, together with gill energetic and structural remodeling
The volume of skin mucus exuded proved to be an informative parameter: an exacerbated expenditure of energy was recorded in the hypersaline condition, and to a lesser extent in hyposaline conditions, with regard to control values

Summary

Introduction

Wild European sea bass (Dicentrarchus labrax) moves seasonally from seawater to freshwater environments and vice versa, including coastal areas, lagoons, estuaries and other parts of rivers [1,2,3,4]. Varsamos et al [1,2] measured blood osmolality at larval and juvenile stages, while Jensen et al [7] studied the effect of salinity on osmoregulation and branchial Na+ /K+ -ATPase In those studies, the authors suggested that the acclimation process was completed in four to eight days. Within the first few days, a classic pattern develops known as “crisis and regulation”, which consists of an initial phase of blood metabolic and osmotic changes, followed by a phase of regulation, when osmoregulatory and metabolic parameters achieve a steady “normalized”

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