The least number of fish that could be in the aquarium is when each habitat has the minimum number of fish, which is 15. Since there are 32 habitats, the least number of fish is 15 x 32 = 480 fish.
The greatest number of fish that could be in the aquarium is when each habitat has the maximum number of fish, which is 24. Since there are 32 habitats, the greatest number of fish is 24 x 32 = 768 fish.
Therefore, the least number of fish is 480 and the greatest number of fish is 768.