Nothing. It won't bother them when the parasitic twin is that small. And when it's small the other fullgrown twin will have a normal lifespan. When both conjoined twins are normal sized, the lifespan will be shorter. So, this specimen should be okay.What will you do with this fish, do you think @emeraldking ?
Correct...a parasitic twin can often live a normal life span .
this wild type guppy Was quite happy swimming around in one of my tanks and lived for 18 months.
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