title: Cardiorespiratory upregulation during seawater acclimation in rainbow trout: effects on gastrointestinal perfusion and postprandial responses.
abstract: Increased gastrointestinal blood flow is essential for euryhaline fishes to maintain osmotic homeostasis during the initial phase of a transition from freshwater to seawater. However, the cardiorespiratory responses and hemodynamic changes required for a successful long-term transition to seawater remain largely unknown. In the present study, we simultaneously measured oxygen consumption rate (ṀO2), cardiac output (CO), heart rate (HR), and gastrointestinal blood flow (GBF) in rainbow trout (Oncorhynchus mykiss) acclimated to either freshwater or seawater for at least 6 wk. Seawater-acclimated trout displayed significantly elevated ṀO2 (day: 18%, night: 19%), CO (day: 22%, night: 48%), and GBF (day: 96%, night: 147%), demonstrating that an overall cardiorespiratory upregulation occurs during seawater acclimation. The elevated GBF was achieved via a combination of increased CO, mediated through elevated stroke volume (SV), and a redistribution of blood flow to the gastrointestinal tract. Interestingly, virtually all of the increase in CO of seawater-acclimated trout was directed to the gastrointestinal tract. Although unfed seawater-acclimated trout displayed substantially elevated cardiorespiratory activity, the ingestion of a meal resulted in a similar specific dynamic action (SDA) and postprandial GBF response as in freshwater-acclimated fish. This indicates that the capacity for the transportation of absorbed nutrients, gastrointestinal tissue oxygen delivery, and acid-base regulation is maintained during digestion in seawater. The novel findings presented in this study clearly demonstrate that euryhaline fish upregulate cardiovascular function when in seawater, while retaining sufficient capacity for the metabolic and cardiovascular changes associated with the postprandial response.
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden; and jeroen.brijs@bioenv.gu.se.
authors.forename: Jeroen
authors.identifier: 0000-0002-3671-5038
authors.initials: J
authors.lastname: Brijs
authors.affiliation: Department of Animal Environment and Health, Swedish University of Agricultural Sciences, Skara, Sweden.
authors.forename: Albin
authors.initials: A
authors.lastname: Gräns
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden; and.
authors.forename: Andreas
authors.initials: A
authors.lastname: Ekström
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden; and.
authors.forename: Catharina
authors.initials: C
authors.lastname: Olsson
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden; and.
authors.forename: Michael
authors.initials: M
authors.lastname: Axelsson
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden; and.
authors.forename: Erik
authors.initials: E
authors.lastname: Sandblom
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D002302:Cardiac Output; D002320:Cardiovascular Physiological Phenomena; D041981:Gastrointestinal Tract / Q000098:blood supply / Q000187:drug effects* / Q000502:physiology; D006339:Heart Rate; D017686:Oncorhynchus mykiss / Q000502:physiology*; D010101:Oxygen Consumption; D019518:Postprandial Period / Q000502:physiology*; D012143:Respiratory Physiological Phenomena; D012623:Seawater; D015854:Up-Regulation
keywords: cardiovascular; feeding; gut blood flow; metabolic rate; saltwater