The most common reasons for goldfish to turn black are genetics and ingestion of colored food. Dark environments also cause goldfish to produce additional melanin, which results in a change in pigment. Disease is uncommo... More »

Ammonia burns are the most common reason that goldfish turn black. High ammonia content in fish tanks causes irritation and trauma to the goldfish's fins. Ammonia burns are white in color and turn black as the goldfish h... More »

www.reference.com Pets & Animals Pets Aquatic Pets

Goldfish often turn black due to genetics, according to FishChannel.com. A goldfish can change color several times over the course of its life. When a goldfish begins turning black, it is often not a serious issue and is... More »

Goldfish often turn black due to genetics, according to FishChannel.com. A goldfish can change color several times over the course of its life. When a goldfish begins turning black, it is often not a serious issue and is... More »

Ammonia burns are the most common reason that goldfish turn black. High ammonia content in fish tanks causes irritation and trauma to the goldfish's fins. Ammonia burns are white in color and turn black as the goldfish h... More »

www.reference.com Pets & Animals Pets Aquatic Pets

Goldfish are omnivores and should be fed a variety of food types. Their diet can include high carbohydrate goldfish flakes, shelled peas, blanched vegetables, daphnia, bloodworms and brine shrimp. More »

Goldfish may stop eating due to overfeeding, boredom with their food, stress or sickness. Poor water quality or a stressful environment can also make fish avoid food. More »