Goldfish are difficult to sex unless mature and in breeding condition. It is possible that the presence of veins is an indication of a bacterial infection. But then again, the cultivars can give the impression of a problem and it is only a part of the intended phenotype. for instance, there are very obese goldfish, looking like they have dropsy - but are perfectly fine.

Thank you! If the fish did happen to have a bacterial infection, what other symptoms would be present?

The fins would look faded, eaten away, gray-brown. Death would be within a day or two. You may just have a fish whose genetics bring out veins as some goldfish appear to have dropsy.