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Fish Like Water - Skwala Fishing

Fish Like Water

In a shocking new development, science has proven, once and for all that FISH LIKE WATER. I know, this is difficult to accept. Turns out that in every one of the roughly 56 billion photos I have of myself holding fish that don’t look nearly as big as I remember them, those fish were pissed. Well, if you want to get technical, they were experiencing hypoxia and their bodies were filling with stress hormones—potato, potahto.


Sarcasm aside, how we handle fish matters. Lately, we’ve been thinking about how we can do more than talk about conservation. Most of you reading this are real anglers, the 10% or so who actually catch fish. We release the vast majority of those fish, and if we’re going to let them go, seems like we should do our best to ensure they actually survive.


So, we invited Sascha Clark Danylchuk—executive director of Keep Fish Wet—to explain some of the basic science behind why fish prefer to remain in water and how we can all do more than hashtag conservation the next time we go fishing.


Keeping fish in the water and out of the air is one of the three most important actions an angler can take to ensure that each fish they release is as heathy as possible. Damage from deep hooking remains the number one cause of mortality in fish we catch with hook and line, but we can’t always control how a fish gets hooked. Air exposure, on the other hand, is completely within an angler’s control.

 A big brown trout in the net.

Sometimes a big fish in the net is all you need. 

Like humans, fish need oxygen, but fish get their oxygen from the water in the form of dissolved oxygen, not the air (yes, there are a few exceptions, species like tarpon can gulp air, but they still primarily rely on dissolved oxygen in the water). Fish respiration (“breathing”) involves moving water into their mouth and over their gills, whether by pumping it or swimming with their mouths open. 


Salmonids (like trout) chiefly respire by pushing water over their gills in a process called buccal pumping. They close their operculum (gill covers) and open their mouth to take a big gulp of water, then close their mouth, open their operculum, and push the water out over their gills.  This coordinated movement enables fish to regulate their respiration.


You know those awesome slow-mo videos where someone lifts a huge, kyped brown trout out of the water and the fish is opening and closing its mouth…yeah, that’s a stressed fish gasping…for water. Maybe you’ve even seen it first-hand.


First of all, fish experiencing stress need even more oxygen, say right after they just got done fighting for their lives at the end of your line. Lack of oxygen (hypoxia) caused by taking a fish out of the water leads a cascade of additional physical and physiological reactions. Their gill filaments (which are covered in mucus and function when floating in water) collapse and adhere together; their stress response gets further triggered, which increases the production of the hormone cortisol as well as glucose and lactate; they suffer ion imbalances and changes in blood pH. In short, they’re pretty pissed (see intro). All of these reactions are temporary and reversible, but the longer a fish is held out of water, the more severe the impacts, and the longer it takes to recover. Full physiological recovery from even brief air exposure after angling can take at least an hour and often several.

So what can you do?  Simple, keep their mouth and gills fully submerged as much as possible.  This paper, written in 2015 by Cook et al., recommends that fish be held out of water for no more than 10 seconds. If you’re good at what you do (and I know you are), that’s plenty of time to remove a hook, and even get a photo. Photos of fish out of the water should be dripping profusely.

 Brown trout being lightly lifted out of the water.

A simple lift out of the water is plenty to get the shot. 

Over the past 30 years, fisheries scientists and anglers have begun to realize the impacts that recreational angling can impose on fish survival and population health—even when a fish is caught and released. Many of our most treasured species are caught repeatedly over their lifetime or even within a single season. As such, getting more anglers to learn and adopt science-based best practices for catch-and-release is an essential step towards resilient and sustainable recreational fisheries.


About Keep Fish Wet 

At Keep Fish Wet, we help anglers release fish successfully. We make the science of catch-and-release accessible and understandable and are committed to providing science-based best practices for those fish anglers release. Visit for more information. 


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