They therefore consume more oxygen weight for weight, and allowance is made for this to the extent that 1 ounce of 1/2-inch fishes is allowed five times the oxygen consumption of 1 ounce of 21/2 -inch fishes, and each ounce of 6-inch fishes is allowed rather less oxygen than that of 2 1/2-inchers. The base line is the 2 1/2 -inch tropical fish, which is allowed 20 square inches of surface area a generous allowance and all estimates should be divided by 3 for cold-water fishes and by 6 for fancy goldfish varieties. The 20-square-inch allowance is intended to permit further growth and good health.
The fishes would not be expected to show distress if their numbers were doubled, but they would not flourish so well. The estimates are clearly approximate and could be misleading in special cases, but from experience it is felt that they are a much better guide than other current recommendations. It will be apparent to the thinking reader that fat fishes of the same length are likely to use more oxygen than slimmer fishes, but this fact is fortunately minimized by the greater activity and therefore greater oxygen need of the slimmer, minnow-like types.
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