The principles stated in the two preceding sections would also be applicable where the specified operations are performed on perishable byproducts. Any operation performed on perishable fish scraps, an unsegregated portion of which is to be canned, would come within the canning (not the processing) part of the exemption. Fish-reduction operations performed on the inedible and still perishable portions of fish resulting from processing or canning operations, to produce fish oil or meal, would come within the processing part of the exemption. Subsequent operations on the oil to fortify it would not be exempt, however, since fish oil is nonperishable in the sense that it may be held for a substantial period of time without deterioration.