Answer:
True
Explanation:
In order for the breeder to know if the long fined fish are homozygous. He will have to cross the Long finned with short finned
If the long finned was homozygous, all the F1 will be long finned zebrafish. This is because long fin is dominant over short fin.
However, if the long finned zebrafish were heterozygous. The cross will produce two long finned and two short finned zebra fish.