Why Corydoras Catfish Cannot Live with Goldfish

I do hours of research before bringing a fish home. I go through my personal library, the local library, fish keeping forums and websites. However, I still messed up when it came to a little corydoras catfish that I put in my 20 gallon goldfish tank. Within five days, the corydoras had disappeared. I took the tank apart and found a skull. Those were the only remains I ever found.

If it turns out there is a Hell, sticking a little corydoras catfish in my goldfish tank will be the reason why I’ll be sent there. Ignore what anyone else tells you and do not make the mistake I did. Corydoras catfish are classified as tropical fish. According to The Everything Tropical Fish Book (Everything Books; 2000) tropical fish and goldfish often attack each other.

The Algae Problem

Why did I bother getting a corydoras in the first place? Algae were getting out of hand in the goldfish tank. I don’t have this problem in my tropical fish tank because a common plecostomus lives there. But a common plecostomus can grow up to two feet long. I wanted something smaller that loved munching on algae. One of my reference books, Goldfish: A Complete Pet Owner’s Manual (Barron’s; 1985) recommended the Corydoras sterbai species.

So I looked up information on the corydoras or “cory.” There are numerous species of bottom-feeding catfish. They need to live at a slightly higher temperature than a goldfish bowl, but I had a heater in my goldfish tank and keep the water around 70 to 72 degrees Fahrenheit, which is about what a cory needs. Many corys available in pet stores only grow to one or two inches long. That seemed perfect for my algae problem.

The Group Problem

After my cory died, I discovered the big mistake I made. Smaller cory species do best in small groups of at least three corys. My cory saw mirror images of himself in the glass walls. Although fish are castigated for being stupid, this cory did not seemed fooled by a reflection. Being alone stresses out the cory – perhaps because it knows that it will soon be eaten by other fish.

Corydoras catfish are described as “armored catfish” because they have some spines on their backs, including a very sharp one on their dorsal fin. I saw the goldfish try to nip at the cory but always encountered the sharp dorsal spine. I also had small hiding spots in the tank for the cory, such as behind two thick plastic plants stuck together.

The Goldfish Problem

If you have kept goldfish for more than ten minutes, you will be aware that goldfish pump out far more waste matter than tropical fish of the same size. The poop is visible, but they also urinate. This waste matter makes the ammonia content skyrocket in the water. I had a powerful filter in my tank and was prepared to clean the tank every other day so that the cory wouldn’t be overwhelmed by goldfish pee.

Goldfish are appetites with fins. They not only eat blood worms, but insects that accidentally plummet into the tank, live plants, frozen peas and fertilized or unfertilized goldfish eggs. If you look at the ingredients of commercial fish food, you’ll see that they contain fish. I still have no idea how the goldfish managed to kill the cory, but they wasted no time in eating him. They would have eaten the skull had I not removed it from the tank.

In Conclusion

There is no shortcut when it comes to managing your algae problem in a goldfish tank. A corydoras catfish or other algae eater is not a humane solution because it will soon be eaten by the goldfish. Your twelve cent goldfish may appreciate an eight dollar cory as a meal, but you won’t.

The RSPCA of Australia lists three freshwater fish species that can live with goldfish, as long as the fish are about the same size as the goldfish. This list does not include cory catfish, but does include:

• · Danios
• · White cloud mountain minnows
• · Gold medaka

But to be on the safe side, just keep goldfish with goldfish.