goldfish turning black

Goldfish turning black may be natural coloration. Color change is quite normal for these types of fish, and other freshwater fish as well. Spotted gold and white fish often turn white with age, and sometimes solid gold. White fish have yellow fins, and black fish may turn orange as they age

Uneven black blotches that develop in a short period of time could indicate the fish was recently poisoned by ammonia, and is now healing. Ammonia burns are whitish, however, they darken during the healing process

Ammonia burns are not uncommon, as ammonia forms from the waste our fish create. If the cycle hasn’t begun, completed, or breaks for some reason, the fish are at risk of being poisoned