The DNA of an organism determines its physical characteristics and what it is capable of doing with the organs in its body.
Yellow perch and walleye are two species of fish. They have a lot of common characteristics; for example both the fish have characteristics that enable their survival under water, they can breathe under water; both the fish have a similar body structure; they reproduce in the same way and produce eggs which hatch to give birth to offspring. For this the DNA of the fish would need to have many common characteristics. This follows from the fact that similar DNA structures would result in similar characteristics in the organisms.
On the other hand deer are not fish but mammals and share few characteristics with fish. The degree of similarity of the yellow perch DNA to that of the DNA of a deer is very small.