A dichotomous key is a tool used to identify organisms. It has several steps, in each of them one of the alternatives needs to be chosen and then they take you to a new step until the organism is identified.
In this case, the steps would be the following:
1a If fish shape is NOT long and skinny, go to step 3
3b If fish has one eye on each side of the head, go to step 5
5b If fish does not have spots, go to step 7
7a If fish has stripes, go to step 8
8a If fish has a v-shaped tail, it is a squirrel fish.
This means the answer is A) squirrel fish