Finsights #3 – A classic air exposure paper

by Sascha Clark Danylchuk

Rainbow trout resting before release. Bryan Huskey photo.

Rainbow trout resting before release. Bryan Huskey photo.

For the first Finsights translation I wanted to start with a classic manuscript about air exposure and fish, and arguably, the paper that started it all.  The paper (linked here and at the bottom of this page) is titled “Physiological effects of brief air exposure in exhaustively exercised rainbow trout (Oncorhynchus mykiss): Implications for ‘catch and release’ fisheries” and was published in the Canadian Journal of Fisheries and Aquatic Sciences in 1992 by Ralph Ferguson and Bruce Tufts.

What did they do?
In this study, the scientists compared three groups of rainbow trout:
    •    Fish that were exercised
    •    Fish that were exercised and air exposed (for 60 seconds)
    •    A control group of fish that were neither exercised nor air exposed
Because this experiment was performed in a lab, chasing trout around the tank was used as a proxy for exercise, which is how scientists think of angling or fighting a fish.  

They then measured a bunch of different blood parameters that are used as indicators of stress.  I don’t want to go into the details of blood chemistry here – it can be confusing and I don’t think necessary to understanding the main points of this study – but I do want to point out that this is a very common way to look at the effects of angling on fish.  

Lastly, the scientists looked at the survival of fish in each of the three groups and also added another group that was exercised and air exposed for 30 seconds, but where no blood samples were taken.  

What did they find?
    •    Air exposure made a big difference!  
    •    Rainbow trout that were air exposed were more stressed and exhausted than any of the other fish.
    •    More fish that were air exposed died compared to those that were just exercised.  Figure 5 is easy to understand and gives the details of survival for each group (treatment, in science speak).

Excerpt from “Physiological effects of brief air exposure in exhaustively exercised rainbow trout (Oncorhynchus mykiss): Implications for ‘catch and release’ fisheries” and was published in the Canadian Journal of Fisheries and Aquatic Sciences in 1992 by Ralph Ferguson and Bruce Tufts.

Excerpt from “Physiological effects of brief air exposure in exhaustively exercised rainbow trout (Oncorhynchus mykiss): Implications for ‘catch and release’ fisheries” and was published in the Canadian Journal of Fisheries and Aquatic Sciences in 1992 by Ralph Ferguson and Bruce Tufts.

Why didn’t the air-exposed trout survive? The scientists argue that the trout that were air-exposed died because fish gills don’t work in air.  Gills consist of tiny, delicate structures, called lamellae, where oxygen exchange occurs.  Water flow across the lamellae is essential for proper functioning and for a fish to breathe (oxygen in, carbon dioxide out…just like us).  When fish are lifted out of the water, the lamellae collapse and stick together and the fish can’t get any oxygen.  

Imagine running a marathon and then being forced to hold your breath – your body (and likewise that of an angled fish) would be deprived of oxygen at the precise moment that you needed it the most.

Rainbow trout lifted slightly as it's released. Bryan Huskey photo.

Rainbow trout lifted slightly as it's released. Bryan Huskey photo.

Why is this study important to anglers?
The authors end this paper by making a very important point:
Because this study was performed in a lab, with hatchery rainbow trout, and with exercise as a proxy for angling their results are not intended to be predictive of what would happen in an actual angling event. BUT, their results do clearly indicate that air exposure is important and can have a big impact on the well-being and survival of angled fish.

This paper got the scientific community to begin to start thinking about the different parts of an angling event (air exposure, hook type, fight time, etc), and how each might influence the stress and survival of fish.  Since this paper, the scientific community has done much more on stress related to angling, and with many more species, especially wild fish being angled in natural settings.

Lastly, I just listened to an excellent interview titled “Why should we believe in science?”  If you are still curious about the scientific process I enthusiastically recommend this eloquent interview with Naomi Oreskes, as well as her TED talk on the same subject.  

Happy fishing!
Sascha Clark Danylchuk


 Click here to view "Physiological effects of brief air exposure in exhaustively exercised rainbow trout (Oncorhynchus mykiss): Implications for ‘catch and release’ fisheries”

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