Astudy is being done to test the affects of habitat space on the size of fish populations. different sized aquariums are set up with six goldfish in each one. over a period of six months, the fish are fed the same type and amount of food. the aquariums are equally maintained and cleaned throughout the experiment. the temperature of the water is kept constant. at the end of the experiment the number of surviving fish are surveyed.

Although not specified, I am assuming that you want to identify the different variables and groups of this case. To answer this, the different typical factors that make up an experimental set up include: 1) dependent and 2) independent variables; 3) controlled variables; as well as the 4) control and 5) experimental group.

The dependent variable in this case is: the size of the population. While the independent variable is: the habitat space. Controlled variables in this experiment include: type and amount of food, cleanliness of the aquarium, and water temperature. The experimental group are simply the fish being observed. There are no controlled groups in this case depending on your definition. Controlled groups are usually the reference point or standard in experimental setups but this experiment wants to look at the differences of the goldfish with each other and not necessarily to a one particular goldfish and hence no controlled group.

The dependent variable is called as such because it is the one that changes depending on the factors given and is usually the one being observed. The independent variable is named as such because it remains the same throughout the experiment.

Hydrosphere is the correct answer