How changes in salinity modify patterns of gastrointestinal motility in the intestine of freshwater barramundi

Salinity is a fundamental geophysical property of water that continuously challenges the physiology of teleost fish. The gastrointestinal tract of teleosts plays a pivotal role for osmoregulation in both marine and freshwater species. Despite this, little is known about how salinity influences gastrointestinal motility. Here, we characterised the patterns of intestinal motility in a euryhaline species, the barramundi (Lates calcarifer), for the first time; and determined how changes in salinity modify these patterns. Motility patterns were qualitatively and quantitatively characterised in ex vivo intestinal preparations from barramundi acclimated to a range of environmental salinities (0, 3, 6, 15 and 24 ppt), representative of hypo-, iso- and hyperosmotic conditions. Recordings of ex vivo intestinal preparations revealed that barramundi exhibit multiple distinct intestinal motility patterns that are responsive to mechanical and pharmacological manipulation, as well as changes in environmental salinity. Bayesian analysis revealed significant differences in the frequency, speed and extent of prominent motility patterns between hypoosmotic (0-9 ppt) and hyperosmotic (12-24 ppt) conditions. Findings show that mechanical distention results in a normalised frequency across the salinity gradient. Pharmacological blockade of synaptic transmission in the enteric nervous system revealed divergent motor responses between intestines derived from fish acclimated to hypo- and hyperosmotic conditions. Taken together, we suggest that intestinal motor patterns in barramundi are modified by environmental salinity which may involve different degrees of plasticity of enteric neuronal functions.