There's an Entire Scientific Industry Focused on Making Mutant Fish

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How do you get fish to develop a third set of chromosomes? This is something that many smart people have been working on for a long time. In fact, triploid fish are the only legal kind of fish to farm in many areas. Learn why we need to screw around with fish DNA, and how to do it.

As we learn that we can’t rely on the oceans to give us the amount of fish we want, aquaculture has become more and more important. Scientists have had to get innovative in order to raise the sheer amount of food necessary for the population, and to minimize the environmental effects of fish farming itself. Recently, they’ve been concentrating on the bane of the modern fish farmer—fish puberty.


Getting into mating shape means that fish concentrate on developing sexual characteristics and filling up with eggs. It also means that they stop eating, because it’s time to go on a journey and spawn. Between the extra energy expenditure and the fasting, the carefully-fattened fish suddenly start losing weight. Sexuality isn’t just a problem for farmers. Farmed fish, if they get into local rivers and streams, can wreak havoc. Either weird, bulked-up fish start mingling their genes with the local wild fish, or invasive species breed and take over.

To keep farmed fishes’ rampant sexuality from ruining everything, scientists have started working hard to scramble a fish’s genes. Amazingly, they’ve found ways to do it en mass. One incredibly popular way is to create “triploid” fish. These fish have an extra set of chromosomes, which renders them sterile for life. The procedure, at least for some species like carp, involves “shocking” their eggs with sudden changes in water pressure. It’s simple and so reliable that it can be made a legal standard. In Midwestern and Southern United States, it’s only legal to use or farm grass carp if they’re triploid. A less-easy method involves injecting adult fish with antibodies which will prevent their offspring from developing gonads.


There are even projects that focus on learning how to detect whether or not fish are sterile. (It’s difficult to only look at a fish and figure out if it’s fertile or not. You have to try to flirt with them and see if they respond.) Even in the case of triploid fish, it usually takes tens of thousands of dollars worth of equipment, and a lot of time. But a recent discovery, that triploid fish have slightly differently-shaped hemoglobin, might cut that time down, and allow environmental researchers taking surveys of fish in the wild to figure out if they have an invasion on their hands with a blood sample, a few minutes, and a microscope. This allows them to weed out the non-mutants. It’s like X-men, in reverse.

Top Image: Kasper Sorensen.