They need an independent variable, in this case it should have been the fish food. Everything should be identical except the fish food, from what I read , it doesn't say anything about what type of food they used, or the dosage.
Answer:
i cant see the questions please send me again
I would say immigration only.
emigration would theoretically reduce the genetic variation as unique individuals leave, but immigration would bring unique traits into circulation in an ecosystem.
I'm not super great at biogy tho so this might not be right... :)
