Why is my white fish attacking my black goldfish and making it white?

It looks like a species of gourami. Most can be kept in a community tank with other fish. The black may be caused by high ammonia levels. Submit a water sample for testing or use a liquid home test kit to check chemistry. Ammonia can kill fish if levels are high enough. Partial water changes can be done daily to stabilize chemistry and maintain water quality. Use only aged or conditioned water that is temperature matched to prevent further stress or shock. My preferences for water conditioners include AmQuel Plus, NovAqua and StressCoat.

This could be due to having a tank that is too small. 6 goldfish in one tank poses several potential issues. Ideally, 1 fish should have a 20 gallon tank with an additional 10 gallons provided per extra fish. This would mean they should be in at least a 70-75 gallon tank. The reason being goldfish produce a larger than average bio-load (wastes) that can quickly overwhelm a small tank and filter. Poor water quality can lead to stress and infection as well as behavioral issues. Depending on their sizes, the present tank could be overstocked leading to bullying and fin nipping. Check the water quality and chemistry. Use a home test kit or submit a water sample for testing. Most pet stores will do this for free or for a small fee. Aim for an absence (0 ppm) of ammonia and nitrites with a nitrate level of 20 ppm or less. Perform partial water changes, if indicated, to stabilize chemistry and maintain or improve water quality. Use only aged or conditioned water that is temperature matched to prevent further stress or shock. Goldfish are cold water fish and do best between 65 F and 72 F (18.3 - 22.2 C). Make sure the filter is rated for at least twice the volume of the tank. If possible, separate out the aggressive goldfish to a different tank to prevent further bullying and injury.

The fish pictured are incompatible in the same tank. Angelfish (black ones) are tropical fish and do best in temps between 73 F and 84 F. Goldfish (white and orange) are cold water fish thriving in temps between 65 F and 72 F. It also appears as if one of your angels has some damage to a tail fin. This is typically due to fin nipping by other fish. You will need to remove either the angels or the goldfish and place them in a different tank. Check the water chemistry for elevated levels of ammonia or nitrites. This can occur in an uncycled tank or a tank that is overstocked. Partial water changes (30-50%) daily can decrease toxin levels. Use only aged or conditioned water that is temperature matched to prevent stress or shock. Confirm your filter is rated for at least twice the water volume of the tank, especially for the goldfish. The links below provide additional information for care of angels and goldfish. http://aquariumtidings.com/angelfish-care/ http://aquariumtidings.com/all-about-goldfish-how-to-care-for-a-goldfish-fish-at-home/

Dwarf gouramis can be very territorial. If your tank is not big enough, one will chase the other. Removing one fish or transfer to a larger tank may be necessary. You can determine sex by looking at the dorsal fin. The male's dorsal fin is pointed, while the female's is rounded or curved.

You can try to provide more hiding areas for your goldfish, and this may allow for it to escape from the pleco. If this doesn't work, you may need to add a barrier into the tank in order to separate the two of them. Barriers can be purchased at your local pet store, and come in a variety of shapes and sizes depending on the type/size of tank that you have. If you are able to gather information on the dimensions of your tank (gallons, length, width, and height) and take that information with you, it may be helpful for the pet store employees. If this is a recent change, you may also see if your pleco is thin - sometimes fish will become aggressive if they are hungry. You can get a general idea of the body condition of your fish by looking at their heads in comparison to their body size - if the head looks too large for the body, that can be an indicator that they are thin. Another way to tell is by looking at the belly - if it looks sunken, that is another indicator that the fish is thin. You may be able to take photos into your pet store to see if the fish are thin, or you can post another question with photos here and we can take a look as well. If you would like to discuss things further, I would be happy to do a consultation with you as well. I hope that gives you a place to start, and good luck!

This "lip wrestling" can indicate aggression if you have two males or if you have a male and female, it may be breeding behavior. You'll need to watch them to differentiate between the behaviors. Males may need to be separated or placed in a larger tank. A female parrotfish will lay eggs on a hard surface in the tank and the pair will take turns caring for the eggs.

Thanks for reaching out about Lucky. First, check water quality for pH, ammonia, nitrites and nitrates. Correct any problems. Is there any other fish in the tank that could be aggressive? Bacterial infections can attack the fins/skin, and if the lesions progress, a veterinary visit is recommended to assess Lucky's health and work on a diagnostic/treatment plan. Any new fish might have introduced parasites. Good luck.