The commissioner defends the position by saying that these fishes are indigenous to the mountain ponds and we need to defend any fish that belongs here.
To weaken the commissioner's position we need to say that these fishes do not belong here.

(A) The suckers, shiners, and chubs in mountain ponds are descendants of fish brought to those ponds by anglers for use as bait in catching the once abundant trout.
Correct.

(B) The state's policy of preserving natural aquatic ecosystems favors the interests and hobbies of one group of people over those of other groups.
interests and hobbies are not mentioned.

(C) Suckers, shiners, and chubs are dull, unattractive fish with none of the graceful beauty of trout.
Aesthetic values of fishes are not important.

(D) People who fish in mountain ponds have a deeper appreciation of nature than do people who never visit such areas.
Out of scope.

(E) A large percentage of the fish in mountain ponds could be eliminated and replaced with trout without seriously disturbing any plants or animals in the surrounding woodlands.
disturbance of plants or animals in the surrounding woodlands is not mentioned.

The explanation is collected from a GMATclub member because I didn't understand it from here.