# Behavioral, haematological, and physiological effects of oxygen‐rich spray after simulated catch and release in rainbow trout (Oncorhynchus mykiss)

## TL;DR

An oxygen-rich spray helps rainbow trout recover faster after short air exposure, with no negative side effects.

## Contribution

The study introduces an oxygen-rich spray as a novel method to aid fish recovery during stressful handling practices.

## Key findings

- Sprayed fish showed faster recovery in head reflexes and orientation after air exposure.
- Treated fish had reduced erythrocyte swelling and stable RBC counts, indicating less hypoxia stress.
- Stress indicators like cortisol and lactate were unaffected, showing the spray does not hinder natural stress responses.

## Abstract

This study investigated the impact of an oxygen‐rich spray on rainbow trout subjected to short‐term air exposure episodes. These episodes can be due to sampling procedures or catch‐and‐release (C&R) practices, focusing on behavioral, haematological, and physiological responses. For this, 12 rainbow trout were divided into two groups: control and oxygen‐rich sprayed fish. The fish were chased for 3 min and exposed to air for 6 s, and blood and behavior parameters were assessed. Simulated C&R resulted in partial physiological reflex impairment across groups. However, sprayed fish exhibited significant differences during recovery in head complex reflex and faster tendencies to regain orientation compared to control. Haematological analyses revealed that the treated group displayed reduced erythrocyte swelling and maintenance of red blood cell (RBC) counts, indicating reduced need for compensatory responses to hypoxia. Meanwhile, stress‐related indicators, including cortisol, glucose, and lactate, remained unaffected by the treatment, suggesting no interference of spraying with the fish ability to launch a healthy stress response. No adverse effects were observed on skin surfaces or gills after an exploratory analysis. Overall, the oxygen‐rich spray exhibited favorable effects, indicating potential benefits in protecting rainbow trout during C&R practices or sampling episodes. Moreover, there is a possible wider application of this methodology to benefit other species of fish subjected to stressors such as aquaculture, research, and fisheries management.