Goldfish swap oxygen for alcohol

Goldfish can survive the winter freeze using a genetic trick that allows them to convert lactic acid into alcohol.
15 August 2017

Interview with 

Michael Berenbrink, University of Liverpool


If you’ve got a goldfish pond then maybe you’ve worried in the past that, come winter, the water might freeze, seal in the fish below and block off the supply of oxygen. But, it turns out that, you don’t need to worry because the fish have a genetic trick that enables them to operate for months without any oxygen. They do it by burning sugars to produce a small amount of energy and a lot of the waste product lactic acid; this would normally be toxic, but then the fish use a specialised set of tailor-made enzymes to convert the lactic acid into alcohol, which they release into the surrounding water. Michael Berenbrink is the one who fathomed it out...

Michael - We looked at goldfish and Prussian carp, a wild relative of them and I’ve always been fascinated by their ability to overwinter in ice covered ponds in the absence of oxygen. When the ice covers the lake, the animals underneath are closed off and they just consume all the oxygen and then they have to deal with oxygen free situations, which is very unusual and not many animals can do that.

When we are without oxygen, humans and other animals - we produce lactic acid. It’s not so efficient but it just gets us a little bit of energy out of our foodstuff. But there’s a problem there that production of this acid is actually bad for you and cannot be tolerated very well.

Chris - This is the same stuff that when you’re taking a vigorous amount of exercise or doing weightlifting or something your muscles begin to burn, and that’s the build-up of lactic acid in the muscle? Because the muscle’s working harder than the amount of oxygen that’s available to it at that time, so it produces lactic acid as a by-product?

Michael - That’s right; this is just in the muscles. The whole animal is without oxygen then every tissue needs to do that, and soon the amount of lactic acid will overwhelm the body and it can no longer function.

Chris - And that would obviously lead to death, which does lead to death in some human patients doesn’t it?

Michael - It does, exactly. These animals can survive this because they’ve found a trick to convert this lactic acid into alcohol ethanol, which is what you have in beverages like beer and wine, and this can diffuse out of the animal via their gills to the environment of water. This is positive because they can survive for a time as long as they have enough foodstuffs to produce lactic acid and convert it to ethanol, but it’s not very energy efficient. What these animals do actually before they overwinter they accumulate foodstuffs in their liver - it’s called glycogen - it’s just carbohydrate, and they can use this when they are under the ice for three months.

Chris - Biochemically, Michael, how do they do this alcohol creation step, because that’s effectively the same thing that yeast does when it turns the products of fermentation into stuff that we like to drink in a beer bottle or a wine bottle; that’s what yeast is doing so how is a fish able to do that?

Michael - What we found out in our research by looking at close related species who can produce alcohol and overwinter, and also can’t. We found that they have these microscopic machines that chanel the foodstuffs into lactic acid. What these animals do is they have a second set of these microscopic machines due to a genome duplication, so that means the whole genetic material, by some accident of nature, was duplicated. So they have two sets and they have evolved to use one of the sets in the normal way and another set to channel the foodstuffs into alcohol production.

Chris - When you say micro machines, these are effectively enzymes, biochemical pathways, and they happened by a genetic trick to have copied them by mistake, probably, in the first instance, but they’ve hijacked one of those copies and now they’re using it to produce alcohol under these certain situations?

Michael - Exactly.

Chris - Can the fish turn this second set of enzymes on and off when they want it so they’re not producing alcohol in the summer, they’re only producing it in this wasteful way in winter when they have to?

Michael - What we found is that this second set is only switched on, and massively switched on in the absence of oxygen.

Chris - Why does this matter? It’s very interesting that you’ve unpicked the genetics of this and you’ve found how these fish can cope under these extreme environments, but why is this important?

Michael - There’s something called foetal alcohol syndrome, which is - in humans - very important. When the mother drinks alcohol during the pregnancy, foetal development can be severely affected. Our work contributes to this whole body of research by showing that goldfish regularly are exposed to high alcohol levels during their normal life cycles. So these goldfish have evolved ways to deal with alcohol concentrations that are above the drink/drive limit in many countries for months on end. This would severely damage the liver of a human, but we don’t know how Prussian carp and the goldfish are able to sustain this. We think there is something to find out there by looking closer into this mechanism.

Chris - If you do alcohol concentration measure on your average garden pond after a particularly harsh winter, can you detect the alcohol in the water?

Michael - It’s a good question. If you put a goldfish into a glass of water and let it produce alcohol, so if you prevent oxygen to accumulate, even if you have it in that confined compartment it takes about 200 days to get the strength of a glass of beer, so the alcohol that they actually release is minimal. That doesn’t mean that their blood concentration isn’t high, the blood concentration is really above the drink/drive limit


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