|Dr Spot gearing up for Halloween, 26 gallon tank.|
On the other hand basing it on people keeping two goldfish in 2.5 gallon tank is ridiculous.
Goldfish are a type of carp (which is not a small fish). A tank that small basically communicates an intent to kill them young.
And given the lack of cycling of the tank, the size and the stocking density, I would be astounded if all the residents ended the study with the same fish they started out with (this data was not reported in the results).
*Riddick CC (1985) Health, aquariums and the non-institutionalized elderly. Special issue: Pets and the family. Marriage Fam Rev. 8:163–173.