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

Abstract

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.

Effects of Cholecystokinin (CCK) on Gut Motility in the Stomachless Fish Ballan Wrasse (Labrus bergylta)

“…The principle of the spatio-temporal mapping method is based on changes in luminal diameter of the digestive tract over time visualized as heat maps. Types of motility, and the parameters of contractions such as propagating direction, distance, duration, velocity and frequency are identified and calculated directly relying on the spatio-temporal (ST) maps by using a series of different filters, thresholds and criteria to detect contractions (e.g., Brijs et al, 2014, 2017). Image analysis has previously been visualized in ST maps by different proprietary software packages/programs depending on research groups (D'Antona et al, 2001; Hennig et al, 2010; Brijs et al, 2014; Kendig et al, 2016).…”

“…However, examination of gut motility also requires an understanding of the behavior of the whole intact intestine with spatial and temporal distributions of motility patterns along the different intestinal regions/segments. The motility patterns and contraction types in the fish intestine have been described for short intestinal segments in shorthorn sculpin ( Myoxocephalus scorpius ) (Brijs et al, 2014, 2016), rainbow trout ( Oncorhynchus mykiss ) (Brijs et al, 2017), halibut (Rønnestad et al, 2000), dogfish ( Scyliorhinus canicula) (Andrews and Young, 1993), and zebrafish ( Danio reio ) (Holmberg et al, 2003, 2004, 2006, 2007). In fishes, there is a knowledge gap in how gut motility is involved in the regulation of gut evacuation in the different anatomical parts of the digestive system.…”

Nutrient sensing; transcriptomic response and regulation of gut motility in an agastric vertebrate

“…Motility patterns in each period were analyzed from three 30 min. sub-periods based on the experimental design in (Brijs et al, 2014; Brijs et al, 2017). The first sub-period (t1, Figure 1) was the first 30 min.…”

“…Each type of contraction plays a specific role, depending on its amplitude, propagation distance and velocity. Standing contractions (Brijs et al, 2014; Brijs et al, 2017) also called stationary contractions (Huge et al, 1995) or segmentations (Gwynne and Bornstein, 2007b; Gwynne et al, 2004; Hennig et al, 2010) are a set of stationary and rhythmic contractions of the circular muscle, which was first described by Cannon more than 100 years ago (Cannon, 1902; Cannon, 1912). This contraction type participates in the digestion (e.g.…”

“…Another sub-type of propulsive contraction is characterized as a series of high-amplitude contractions that propagate for a longer distance than ripples but at a low velocity. In some fish studies these are called slow propagating contractions (Brijs et al, 2014; Brijs et al, 2017; Brijs et al, 2016; Le et al, 2019a), while in studies of humans and other mammals, the accepted term is “high-amplitude propagated contractions” (Bharucha, 2012; Spiller et al, 1988). These move luminal contents from one section to the next, thanks to their high amplitude (Bharucha, 2012; Husebye, 1999; Kunze and Furness, 1999).…”