A scientist did an investigation on the growth of koi fish. He selected forty newly hatched koi from the same clutch of eggs. He separated the koi into four groups and placed each group in a different sized pond. None of the ponds had any predators that would eat the koi fish. The amount of food available to the koi and the water quality of each pond differed based on the size of the pond. Larger ponds had more food available and better water quality as the fish grew.

After 15 months, the scientist measured the length of each koi fish. Using these measurements, he came up with an average koi size for each pond.

Effect of Pond Size on Koi Fish Growth

Size of Pond Average Length of Koi
500 gallons 18.2 centimeters
1000 gallons 25.6 centimeters
2500 gallons 30.8 centimeters
5000 gallons 35.3 centimeters

Based on the scientist's results, which of the following is true?
A.
Koi fish grow fastest in ponds with poor water quality.
B.
Koi fish grow fastest in ponds with a high population density.
C.
The growth of koi fish is determined entirely by genetics.
D.
The growth of koi fish is affected by the environment of the fish.