What would be plausible control variables for these experiments?

Hey peeps!

So I’m designing an experiment using a computer simulation, and I desssssssssperately need some help :(

The experiment deals with male guppy morphological variation, and I need to test for factors that would affect the amount of “spots” that would be seen over time.

My two hypotheses are:
(1) The colour of the guppies’ habitat (streamwater) would have an affect on the amount of spots (due to phenotypic plasticity), and
(2) The abundance of females would have an affect on the amount of spots

The only problem I have here, though, is that I don’t know what the control groups would be for the 2 hypotheses..

For the first hypothesis, I’m gona set up 3 treatment groups (green coloured water, cyan coloured water and brown coloured water) that will have 20 females and 20 males that are allowed to breed.

For the second hypothesis, there will also be 3 treatment groups (5 females, 10 females, and 15 females) that will have 20 males that are allowed to breed in each treatment.

For BOTH experiments, predators will be absent, and the amount of food sources will be kept constant so that there are no confounding variables.

With that being said, can anyyyyyyyyyyone tell me what the control groups might be? :(

I’m aware that the independent variables are supposed to be kept constant in the control groups, but how do you have an of absence water..when..the guppies live in water? :S More so, If I have an absence of females in the second hypothesis, the guppies won’t breed, and I won’t be able to test if the amount of spots are changing over time :( I. am. so. stuck.