Photoshop :: Match Lighting Of Two Pictures For Scientific Research Project

We do research on the effect of fish food on the color change of the fish's skin. Therefore we observe the fish over multiple weeks and take their picture in our studio environment once a week. In order to track the color change of the fish, all other conditions (lighting, distance etc.) should be exactly the same so that we can compare the average color of the fish over multiple weeks.

The problem is as follows. We have created an studio environment with a light tent and three flashes and fixed them to keep the shooting conditions the same every time. However as you can see in the three images below which are shots of the same fish in three different weeks, the lighting is not the same. We think that since we do shoot 30 fish in each batch, the flash did not produce the same performance for every shot and we got different lighting in each shot.

How can we match the lighting of these shots so that we can compare the color of the fish? We already tried the color match tool however it is no use in this case. Since we want to keep the fish as it is and only adjust the slight lighting difference.