Mystery fish revealed!
After a week and a half, the results are in. Phil Sansom went back to Illumina’s Louise Fraser to see if she could identify our mystery fish. Did you guess right?
Louise - The results just came in yesterday.
Phil - Ready to guess?
Louise - Oh, absolutely! What we got was around 500 million DNA sequencing reads, and we compared them to a database that contains all the species that have ever been sequenced completely. And about 98% of the reads actually didn’t align to anything in the database. Most likely those would be bacterial samples…
Phil - But those aren’t new-to-science creatures, they just haven’t had their genome sequenced yet?
Louise - That’s right, they’re just things that aren’t currently in the database.
Phil - OK, 98% unknowns…
Louise - Of the remaining 2% they broadly fall into four different groups. 95% of the classified reads are bacterial; 5% are from animals, and 1% from plants; and then there’s a tiny fraction that come from fungi and archaea. The most common animal species in the water sample was actually human. But the second-most-common animal was a family of fish called cichlids. And so that’s what we think was in the tank.
Phil - Is that your final answer? Louise, I hate to tell you… it’s not a cichlid! Any other ideas?
Louise - Yeah, so there’s low level of DNA from a number of other animals, such as rice fishes, carp, and even piranhas.
Phil - OK, this is interesting, because it’s actually one of those.
Louise - OK…
Phil - Do you want to guess which one?
Louise - Gosh, I’d like to think it was the piranhas, maybe.
Phil - It is piranhas!
Louise - It is piranhas?
Phil - It was piranhas!
Louise - OK, wow. That was a brave person that took that sample.
Phil - Did you guess right? Our mystery fish is indeed a piranha! Now Louise got piranhas as one of the results, but it was far from top of the list. What’s going on - well, the water in the aquarium tanks isn’t separated from each other, it’s actually filtered through a number of them. So i guess we didn’t make Louise identify a piranha from a piranha tank - so much as identify a piranha from a whole aquarium filled with different fish.
Louise - It would be interesting to know if there are cichlids within the same aquarium, and whether we’re just picking that up from a different tank.
Phil - There are, in quite a few of them.
Louise - Right. That might make sense then. There was also some other interesting DNA sequences that we picked up. Some mouse, or rodent DNA in there...
Phil - You should have all the pieces to the puzzle by now.
Louise - Oh, is it part of the fish food?
Phil - Oh yeah.
Louise - OK, right, that makes sense.
Here’s the audio that was hidden earlier - Phil Sansom learning about piranhas from Tony Sapsford at Frog End Aquatics...
Tony - Do you want me to say what they are?
Phil - Yeah, please.
Tony - Okay, this is the piranha tank. They've got red underbellies, red tails, large eyes. I mean they are only babies have only just got their teeth, so they’re only about 4 inches long at the moment, maybe 5 inches.
Phil - You can barely see them.
Tony - You can barely see the teeth.
Phil - Oh my God, you're putting your hand in.
Tony - It's not gonna hurt me trust me.
Phil - Are you sure?
Tony - Yeah.
Phil - Are they not aggressive?
Tony - Only in like a pack, when they're feeding and stuff like that. Like if he had a sick one in there, they’d annihilate it.
Phil - Am I right to be scared of them, or should I not fear them?
Tony - No. No, it's nothing to be scared of. Unless you're gonna jump into a lake in the Amazon with a whole pack of them, I don't think there’s anything to worry about. Most people who buy fish like that think ‘oh it's great. I’ve got to have a piranha’, but then they get bored of it very quickly because they don't do anything.
Phil - Do people buy them because they think they're being hard?
Tony - Yeah, basically that's it. ‘Oh I got one of them, it’s a piranha’. And all they do is get big and boring.