Tyler is a scientist who is interested in understanding aggression levels and what makes a male stickleback fish a good fighter and defender of his territory. He used sticklebacks he collected from British Columbia to test his hypothesis. In his experiment, 24 males were kept in 6 large tanks, with 4 males in each tank. Tyler watched each of the 24 males every day for 10 days. He recorded the behaviors of each fish when they were competing for territories, defending their territory, and building their nests.

I'm having trouble finding the independent variable and control group in this bit, can someone help me identify it please?