Water metabolism in the eel acclimated to sea water: from mouth to intestine

Upon exposure to seawater, euryhaline teleosts need to imbibe and desalinate seawater to allow for intestinal ion and water absorption, as this is essential for maintaining osmotic homeostasis. Despite the potential benefits of increased mixing and transport of imbibed water for increasing the efficiency of absorptive processes, the effect of water salinity on intestinal motility in teleosts remains unexplored. By qualitatively and quantitatively describing in vivo intestinal motility of euryhaline rainbow trout (Oncorhynchus mykiss), this study demonstrates that, in freshwater, the most common motility pattern consisted of clusters of rhythmic, posteriorly propagating contractions that lasted ∼1-2 min followed by a period of quiescence lasting ∼4-5 min. This pattern closely resembles mammalian migrating motor complexes (MMCs). Following a transition to seawater, imbibed seawater resulted in a significant distension of the intestine and the frequency of MMCs increased twofold to threefold with a concomitant reduction in the periods of quiescence. The increased frequency of MMCs was also accompanied by ripple-type contractions occurring every 12-60 s. These findings demonstrate that intestinal contractile activity of euryhaline teleosts is dramatically increased upon exposure to seawater, which is likely part of the overall response for maintaining osmotic homeostasis as increased drinking and mechanical perturbation of fluids is necessary to optimise intestinal ion and water absorption. Finally, the temporal response of intestinal motility in rainbow trout transitioning from freshwater to seawater coincides with previously documented physiological modifications associated with osmoregulation and may provide further insight into the underlying reasons shaping the migration patterns of salmonids.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Exposure to seawater increases intestinal motility in euryhaline rainbow trout (Oncorhynchus mykiss)

Brijs

Hennig

Gräns

et al. 2017

“…In essence, freshwater fish must be able to combat water gain and ion loss, while the opposite is true for fish found in saltwater environments. Much is known about the physiological processes involved in ion and water regulation, from branchial, intestinal and renal transport (reviewed by Cerda and Finn, 2010;Grosell et al, 2009;Evans, 2008;Ando et al, 2003;Karnaky, 1998) to hormonal regulation (reviewed by Takei, 2008;Manzon, 2002;McCormick, 2001). There are also many euryhaline species that are able to transition between the two extremes of freshwater and seawater.…”

Section: Introductionmentioning

confidence: 99%

Diet influences salinity preference of an estuarine fish, the killifishFundulus heteroclitus

Bucking

Wood

Grosell

2012

SUMMARYUnderstanding the interplay among the external environment, physiology and adaptive behaviour is crucial for understanding how animals survive in their natural environments. The external environment can have wide ranging effects on the physiology of animals, while behaviour determines which environments are encountered. Here, we identified changes in the behavioural selection of external salinity in Fundulus heteroclitus, an estuarine teleost, as a consequence of digesting a meal. Fish that consumed high levels of dietary calcium exhibited a higher preferred salinity compared with unfed fish, an effect that was exaggerated by elevated dietary sodium chloride. The mean swimming speed (calculated as a proxy of activity level) was not affected by consuming a diet of any type. Constraining fish to water of 22p.p.t. salinity during the digestion of a meal did not alter the amount of calcium that was absorbed across the intestine. However, when denied the capacity to increase their surrounding salinity, the compromised ability to excrete calcium to the water resulted in significantly elevated plasma calcium levels, a potentially hazardous physiological consequence. This study is the first to show that fish behaviourally exploit their surroundings to enhance their ionoregulation during digestion, and to pinpoint the novel role of dietary calcium and sodium in shaping this behaviour. We conclude that in order to resolve physiological disturbances in ion balance created by digestion, fish actively sense and select the environment they inhabit. Ultimately, this may result in transient diet-dependent alteration of the ecological niches occupied by fishes, with broad implications for both physiology and ecology.

“…In SW, fluxes of ions and water are reversed. To compensate for such water loss, salmon begin drinking shortly after transfer to SW (Smith, 1932;Usher et al, 1988) and the ingested water is absorbed passively in concert with ions during passage through the gastrointestinal tract (Ando et al, 2003;Sundell and Sundh, 2012;Wood and Grosell, 2012). Excess ions are actively excreted over the gill, predominantly through transcellular and paracellular routes in association with ionocytes in the gill filaments (Karnaky, 1986;Hiroi et al, 2005;Tipsmark et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Differential expression and novel permeability properties of three aquaporin 8 paralogs from seawater-challenged Atlantic salmon smolts

Engelund

Chauvigné

Christensen

et al. 2013

SUMMARYAquaporins may facilitate transepithelial water absorption in the intestine of seawater (SW)-acclimated fish. Here we have characterized three full-length aqp8 paralogs from Atlantic salmon (Salmo salar). Bayesian inference revealed that each paralog is a representative of the three major classes of aqp8aa, aqp8ab and aqp8b genes found in other teleosts. The permeability properties were studied by heterologous expression in Xenopus laevis oocytes, and the expression levels examined by qPCR, immunofluorescence and immunoelectron microscopy, and immunoblotting of membrane fractions from intestines of SWchallenged smolts. All three Aqp8 paralogs were permeable to water and urea, whereas Aqp8ab and -8b were, surprisingly, also permeable to glycerol. The mRNA tissue distribution of each paralog was distinct, although some tissues such as the intestine showed redundant expression of more than one paralog. Immunofluorescence microscopy localized Aqp8aa(1+2) to intracellular compartments of the liver and intestine, and Aqp8ab and Aqp8b to apical plasma membrane domains of the intestinal epithelium, with Aqp8b also in goblet cells. In a control experiment with rainbow trout, immunoelectron microscopy confirmed abundant labeling of Aqp8ab and -8b at apical plasma membranes of enterocytes in the middle intestine and also in subapical vesicular structures. During SW challenge, Aqp8ab showed significantly increased levels of protein expression in plasma-membraneenriched fractions of the intestine. These data indicate that the Atlantic salmon Aqp8 paralogs have neofunctionalized on a transcriptional as well as a functional level, and that Aqp8ab may play a central role in the intestinal transcellular uptake of water during SW acclimation. Supplementary material available online at