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I’d never heard of this topic until the other day, but with a quick search I soon found a lot of other people talking about the same thing. It seems there are anglers all over the place pouring carbonated drinks into their fish in an effort to stop them bleeding from the gills. But can Coke, Sprite or Mountain Dew really help or is it just an old wives tale? For starters, let’s talk about why gills are such an important part of the fish.

Not only are gills the fish’s only means of breathing, they’re also an area where the fish’s blood is very close to the surface, meaning it’s a clear point of vulnerability. As this discussion on Reddit points out, the rest of a fish’s body is well protected:

“Scales are extremely tough. […] Skin is very tough in fish too. It’s a tough organ to pierce, as it should be, and it lies just beneath the scales. […] But, one other thing when it comes to cuts in fish, most of the fishes’ body cavity are below a massive layer of muscle tissue which can be quite thick in some species. It also lacks significant blood arteries and veins in the musculature itself. Thus, most “heavy bleeding” in fish really comes from internal bleeding, not from cuts on the body.”

You’ve probably seen fish yourself with big wounds on their bodies – perhaps inflicted by another fish, a heron, cormorant, otter or a seal. Sometimes it’s hard to believe they survived, but survive they did. But you may also have had experience of hooking a fish deep in the gills. How fragile they seem then. The blood flows and it can seem like it will never stop.

That’s why this discussion on fishing blog, Gink and Gasoline, caught my attention. The author, Louis Cahill, noticed the fish he’d just caught was bleeding from the gills and was hit by that all-too-familiar twinge of guilt. But this is where it gets interesting. As Louis reports:

“Thank God Kent was with me. […] He opened the fish’s mouth and poured the Coke down her throat. As soon as it hit the injured gill the bleeding stopped. It was like magic. I’m not sure if it’s the carbonation or the acid but something in the Coke cauterized the wound. It saved that fish’s life. I know it for a fact because I saw her in that same pool several weeks later…”

This report and Louis’ eye-catching photograph (below), really got my interest, but I found it hard to believe that Coca Cola could contain special healing qualities. So I read the comments… some serious:

“A small squirt bottle of white vinegar works just as well.” (Greg)

…Some not so serious:

“I’ve found that pepsi actually works better.” (Adam)

But I didn’t get a satisfactory answer, so I began searching elsewhere. Here’s what I found on the Colorado Fishing Forum:

“Here is where the soda come into play, that might help to save a fish’s life. Use a soft drink that has some citric acid (Mountian Dew, Sprite, Mellow Yellow, 7UP). Once the fish begin to bleed from the gills or gullet, pour the soda on the affected area. The acid in the soda will make the capillaries shrink and reduce and may stop haemorrhage.”

Hmmm – not overly convincing or scientific. But then, there is video evidence to support the theory. Check this out:

Still nobody has given any scientific reason as to why this works and, while I would love to think there’s a way we can help our injured fish to revive, I’m still feeling a bit dubious. That’s when I found this in the comments to a related Field and Stream article:

“It’s the phosphoric acid in Coke. Fish flesh is susceptible to acid. It causes the wound to “cook” essentially. It’s long been known you can cold cook shrimp in lemon juice, for the same reason. The fish’s wound cauterizes, for lack of a better term, causing blockage to the blood flow.” (Daniel Ettinger)

OK Daniel – you’re confident, I’ll give you that, but are you right? I’m still not convinced. Can phosphoric acid in these soft drinks really stop bleeding? If so, how do you explain the people who claim Sprite also works. Sprite doesn’t contain phosphoric acid; neither does Mountain Dew. And yet, as the video above clearly showed, the bleeding stopped almost immediately. So how do we explain it?

Well, I for one agree with what I read on the Bass Resource website. I think it’s the liquid itself that promotes the healing not an ingredient within it:

“The way a fish’s blood coagulates is opposite that of humans. We humans need air for it to coagulate. Fish, on the other hand, need water.”

Fish, of course, live underwater, so it stands to reason that they need to be in the water in order for their systems to function properly. A fish’s gills may be vulnerable, but it wouldn’t make sense for them to require sugar or acid to be able to heal. Their gills are, in fact, right in harm’s way – especially for predatory fish. Imagine a predator, for instance, swallowing some form of spiny prey like a crayfish or a perch. There’s a good chance they’ll receive a gill injury. They must be able to self-heal, which means their blood must be able to coagulate. But of course, in order for this to happen, the fish in question needs to be in its natural environment.

In other words, pouring a soft drink may well stop a fish bleeding from the gills, but it’s almost certainly a better strategy simply to put your fish back in the water – or in a healing tank – and to let it heal naturally.

[Image credit: Louis Cahill]