Transient cognitive impacts of oxygen deprivation caused by catch-and-release angling

Flink, Henrik 1 ; Berge, Adrian1; Leggieri, Francesca1; Kolm, Niclas2; Tibblin, Petter1

Research facility: Centre for Ecology and Evolution in Microbial Model Systems (EEMiS)

Published Dec 17, 2024 on Dryad. https://doi.org/10.5061/dryad.brv15dvk8

Data files

Dec 17, 2024 version files 3.26 MB

README.md
3.71 KB
y-maze_data.csv

3.26 MB

Abstract

Vertebrate brain function is particularly sensitive to the effects of hypoxia, with even brief periods of oxygen deprivation causing significant brain damage and impaired cognitive abilities. This study is the first to investigate the cognitive consequences of hypoxia in fish, specifically induced by exhaustive exercise and air exposure, conditions commonly encountered during catch-and-release (C&R) practices in recreational fishing. Angling exerts substantial pressure on inland fish populations, underscoring the need for sustainable practices like C&R. While C&R survival rates are generally high, understanding its sublethal impacts is crucial for evaluating the practice's ethical and ecological sustainability. We examined the effects of these stressors on the cognitive function of 238 rainbow trout, using the Free Movement Pattern Y-maze method to assess working memory through navigational search patterns during free exploration sessions. Our results showed that air exposure led to short-term (3-4 hours post-treatment) but transient impairments in working memory, with no long-term cognitive deficits observed at 1 week and 1 month post-treatment. These findings emphasise the high tolerance of fish to hypoxia and support the sustainability of C&R as a tool in fisheries management.

README: Transient cognitive impacts of oxygen deprivation caused by catch-and-release angling

Dryad doi: https://doi.org/10.5061/dryad.brv15dvk8\
Research article doi: https://doi.org/10.1098/rsbl.2024.0527

Description of the data and file structure

Catch-and-release (C&R) stress was simulated using well-established, standardised, and controlled protocols, enabling a clear distinction between the individual effects of exhaustion, oxygen deprivation, and their combined interactions. To achieve this, rainbow trout were randomly allocated to one of five experimental treatments, ensuring stratified sampling based on body length. The treatments were as follows: control (N = 52), exhaustive exercise (N = 46), 60-second air exposure (N = 53), exhaustive exercise followed by 30-second air exposure (N = 42), and exhaustive exercise followed by 60-second air exposure (N = 45). Exhaustive exercise involved chasing fish in a tank (L80:W65:D45 cm) until exhaustion, signaled by the fish being caught by the caudal fin five times. Air exposure consisted of holding fish out of water in a dip net for either 30 or 60 seconds.

Working memory was assessed in eight identical Y-mazes over three 1-hour exploration trials per fish at varying time intervals post-treatment: 3-4 hours (short-term), 1 week (intermediate), and 1 month (long-term). Due to technical issues, video data for 24 short-term and 8 intermediate trials were recorded during the second hour of a 2-hour free exploration period in the Y-maze, instead of the initial hour. Fish movement in each video was tracked automatically using the trackPath function in the R package pathtrackr. Pixel coordinates representing fish positions were recorded and linked to specific maze regions, then recoded to determine the occupied maze arm using a reference image with arm polygons. Each fish's tracked path was plotted to verify tracking accuracy, and manual tracking was adopted when automatic tracking was insufficient. Transitions between arms were converted into sequences of left and right turns and organised into 16 overlapping tetragrams. Thirteen trials were excluded as the fish performed fewer than four turns and therefore could not be organised into tetragrams. Additionally, 40 fish succumbed prior to the intermediate trials due to an accidental laboratory incident, and 16 fish perished prior to the long-term trials for unknown reasons.

Files and variables

File: y-maze_data.csv

Description:

Variables

PITID: Unique identification for each fish
tetragram: Sequence of four left and/or right turns
manual: If the tracking was performed manually or not (if not, automatic tracking was successful)
run: Time interval of trial; short-term (3-4 hours after treatment), intermediate (1 week after treatment), or long-term (1 month after treatment)
treatment: Simulated C&R treatment: control (C), exhaustive exercise (Ex), 60-second air exposure (Air60), exhaustive exercise followed by 30-second air exposure (ExAir30), and exhaustive exercise followed by 60-second air exposure (ExAir60)
notes: Due to technical issues, video data for 24 short-term and 8 intermediate trials were recorded during the second hour of a 2-hour free exploration period in the Y-maze, instead of the initial hour. This information is in the notes.

Code/software

The R script file (Code for Transient cognitive impacts of oxygen deprivation caused by catch-and-release angling.R) include all scripts used in our analyses. The scripts were created using version 4.4.1 (2024-06-14). Annotations are provided throughout the script.