Could mackerel gonads change the world?

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Scientific trials are underway to see if one fish can produce the offspring of another. If they can, it'll change the face of breeding and conservation as we know it, says Nathan Hill.


Here's a chain of thought. If I add enough 'ifs' then eventually an ant can lift an elephant. I'm sure you can see where I'm going with that, but let me illustrate just in case. 'If' the ant happened to be big and heavy enough to move a mechanical lever, and 'if' an elephant happened to be stood on a strong enough pallet on a forklift, and 'if' the two creatures happened to be in that scenario together, and 'if' the ant somehow moved the lever then perhaps, just perhaps the actions of the ant would lift that elephant.

Yeah, there's a bit of wordplay involved, a little juggling of meaning, but with enough 'ifs' and ant can indeed lift an elephant. Add as many imaginary stages as you want, and eventually you'll get there.

There's currently something similar going on in the world of aquatics, and as a collective industry, we should all be crossing our fingers, toes, hair, pets, legs, and anything else we have to hand, and wishing it the best. 'If' it goes right, then we can overcome not just some ethical woes of wild collection, but also those of sustainable practice in general. We could control genetic lines and purity, though as a corollary we could also capitalise on quirks and gimmicks to make novelties to order.

What I'm referring to is the concept of species surrogacy. Specifically, I'm talking about the kind of species surrogacy currently being trialled by Goro Yamazaki at the Tokyo University of Marine Science and Technology.

What this surrogacy involves is taking the genetic blueprint from one fish, in the form of extracted stem cells, and injecting those cells in to the fry of another fish. The hope is, that inserted in to the right part of the body(i.e. the reproductive organs), these stem cells will imprint themselves upon the host fish's gonads to create reproductive tissues for the donor species. Quite literally, 'if' I can take the sex cells of one fish and 'if' I can get them to grow in another's body, and 'if' I get a successful spawn, then I could end up with one species of fish producing a few thousand viable offspring of another fish, without even realising it. If, if, if...

...maybe.

If that sounds science fiction, then you'd be forgiven for expecting this tale to twist into damning parables and apocalyptic warnings of marine frankenmonsters invading Nagasaki. But the science is pretty solid, and expectations high.

Goro's present aim is to introduce the reproductive organs of Tuna in to the bodies of Mackerel — the latter a far more prolific breeder than the former, and more abundant too. Despite this year's surprisingly lax start to the Tuna season, the fish remains not just as an institution of Japanese consumption (a quarter of all caught Blue fin Tuna are destined for Japanese plates) but also as a flashing beacon on the warning panels of the IUCN Red List of Endangered Species. For the person who can farm vast numbers of Blue fins — a notoriously hard species to captive breed — huge fortunes both financially and morally await.

But. There's always a but.

So far the bounties of the enterprise have amounted to nought. Though the stem cells may have influenced gonad development in mackerel, spawns were unsuccessful, and this is hypothesised to be down to temperature issues. But the future, and the concept itself, looks bright. And if adult mackerel can pump out baby blue fins to the tune of thousands at a time, then pressures on wild stocks – reintroduction at the least – will be optimistic instead of hopelessly forlorn, as they presently are. We can only wait and see.

But Tuna is just one of many thousands of fish out there. There are many other long-term prospects for this potential breakthrough.

For one, difficult to spawn species need no longer be a bother, as long as easy, and genetically compatible species are available. Why bother with those awkward Scleromystax squabbles between males, if I've just got the bodies of Bronze corydoras, Corydoras aeneus, pumping out the fry at a rate of knots? And how about Dwarf gouramis being pumped out of Dwarf gourami iridovirus-free parents, like blue Trichopodus species instead? There are a lot of uses for this technology.

Of course, this is before I even mention rare or endangered fish. Hypancistrus zebra? Inject the cells in to a randy Ancistrus and be done with it. From a hobby point of view, this makes a big difference. Databanks of DNA could allow for reintroduction of extirpated species at any time, and even rare teleosts could become as common as guppies overnight.

I'm sure that by now you've thought up a scenario of your own where technology like this will make all the difference. Whether it's to ensure pure lines, or to bring back something that's borderline extinct, we can all imagine a use for a surrogate fish.

But, as always, I'm sure there will be detractors who will need hearing out. With genetic tampering comes responsibility, and when we're messing with a fish's fecundity we need to be careful of the outcome.

As an absurd example, let's also say 'if' I took the stem cells of a Sea lamprey, and 'if' I managed to get them to infuse themselves on to the gonads of a Sunfish (Mola mola) and 'if' that Sunfish happened to produce its standard 300 million young (Mola mola are the most fecund fish on the planet) then I've just caused a world of pain to the marine ecosystem. 300 million is a lot of lampreys. They'd suck your veins dry in a minute.

But that really is absurd. Nobody would want to do that, nor would they intentionally even investigate it, unless there happened to be a sudden and cataclysmic lack of Lamprey, which is unlikely. Assuming that codes of conduct are adhered to, ethical committees obeyed and respected, and good modelling techniques of outcomes assessed, then it's hard to see at this stage what could go wrong.

Yeah, there are the 'ifs' of unethical traders. So, 'if' I get a crazy runt that looks like Blinky from the Simpsons, and 'if' I can inject its stem cells into a goldfish and pump out a string of those runts, then I can call them Simpson fish, and rake in a fortune from a frivolous public. Used badly, such technology could drive up the numbers of anomalies like infertile fish (through choice, where breeders want to keep the prices of their stock high – why sell fertile young for others to breed when you've got a monopoly?), and create all manner of commercial skulduggery.

But that's still a lot of 'ifs'. If this all comes together, and if scientists use the technology well, then we could be on the precipice of a greater breakthrough than any of the mainstream press is paying attention to.

That's 'if' it works, of course. Otherwise it's back to the start, we're no closer to making the world a better place, and Tuna are still highly endangered. But then 'if' they weren't then we'd not have the impetus to develop this technology. There's a cruel irony in that.