Physicochemical properties of the dissolved organic carbon can lead to different physiological responses of zebrafish (Danio rerio) under neutral and acidic conditions

Abstract

Previous studies have suggested that the capacity of natural dissolved organic carbon (DOC) molecules to interact with biological membranes is associated with their aromaticity (SAC340); origin (allochthonous versus autochthonous, FI); molecular weight (Abs254/365); and relative fluorescence of DOC moieties (PARAFAC analysis). These interactions may be especially important when fish are challenged by acidic waters, which are known to inhibit the active uptake of Na+ and Cl‐, while stimulating diffusive ion losses in freshwater fishes. Therefore, zebrafish were acclimated (7 days, pH 7.0) to five natural DOC sources (10 mg C/L), two from the Amazon Basin and three from Canada, together with a “no‐added DOC” control. After the acclimation, fish were challenged by exposure to acidic water (pH 4.0) for 3 h. Osmoregulatory parameters were measured at pH 7.0 and 4.0. Acclimation to the five DOC sources did not disturb Na+, Cl‐ and ammonia net fluxes, but resulted in differential elevations in Na+, K+ATPase and v‐type H+ATPase activities in fish at pH 7.0. However, after transfer to pH.4.0, the control fish exhibited rapid increases in both enzymes. In contrast the DOC‐ acclimated animals exhibited unchanged (Na+, K+ATPase) or differentially increased (v‐type H+ATPase) activities. Na+, Cl‐ and ammonia net fluxes remained unchanged in the control fish, but were differentially elevated in most of the DOC treatments at pH 4.0, relative to the same DOC treatments at pH 7.0. Correlations between the osmoregulatory data the DOCs properties highlight that the DOC properties drive different effects on gill physiology.

Fish-microbe systems in the hostile but highly biodiverse Amazonian blackwaters

“…DOC molecules can bind directly to the surface of gill cells (Campbell et al , 1997), but how exactly they interact with fish is still unresolved. Moreover, the protective roles of DOC are highly dependent on its chemical characteristics or integrity (Sadauskas-Henrique et al , 2019, 2021). In aquatic ecosystems bacteria are known to transform DOC in different ways (Mou et al , 2007).…”

“…However, some DOCs can also have toxic effects on fish at low pH (Kullberg et al , 1993) or have a hormesis effect whereby protective at certain concentrations or pHs (Holland et al ., 2014b; Steinberg et al ., 2008). Recent studies suggest that the protective roles of DOC depend on its chemical characteristics or integrity: humic DOC exacerbated rather than protected against ionoregulatory disturbance both in zebrafish ( Danio rerio ) and Amazonian tambaqui ( Colossoma macropomum ) (Sadauskas-Henrique et al , 2019, 2021). Overall, the protective role of humic DOC is promising, but current results are contradictory and the processes involved are still unresolved.…”

Important role of endogenous microbial symbionts of fish gills in the challenging but highly biodiverse Amazonian blackwaters

“…DOC molecules can bind directly to the surface of gill cells 20 , but how exactly they interact with fish is still unresolved. Moreover, the protective roles of DOC are highly dependent on its chemical characteristics or integrity 25,26 . In aquatic ecosystems, bacteria are known to transform DOC in different ways 76 .…”

“…However, some DOCs can also have toxic effects on fish at low pH 24 or have a hormesis effect whereby protective only at certain concentrations or pHs 23 . Recent studies suggest that the protective roles of DOC depend on its chemical characteristics or integrity: Humic DOC exacerbated rather than protected against ionoregulatory disturbance both in zebrafish (Danio rerio) and Amazonian tambaqui (Colossoma macropomum) 25,26 . Overall, the protective role of humic DOC is promising, but current results are contradictory and the processes involved are still unresolved.…”