The Oscar Fish

A budding hobbyist walks into a pet store and peruses the rows of tanks. He is drawn to a tank filled with 2 inch fish having a green color with red blotches and a cool eyespot or two. The fish all rush to the front of the tank, watching his every move. He is instantly taken with these fish and must have them. After consulting with the kid who is working there, he takes home 2 or 3 and a 20 gallon set up. So starts the rocky road of most Oscar owners.


Oscars are one of the most personable and interesting of the fish available to the fresh water hobbyist. This is what makes them an excellent pet, and also what leads to them being purchased by people who are in no way prepared to deal with what that cute 2 inch fish turns into. A foot long (or more) eating machine that can foul a tank quicker than all but maybe Gold fish. Hopefully this article will clear up some myths and help you to enjoy one of my all time favorite fish.


First, a little history. Oscars (Astronotus ocellatus) were first introduced to the hobby in the early 30’s. It seems quite a few of the fish we consider to be common were first imported in this time period. When originally imported, these fish were not called Oscars. The common names given them were velvet cichlid and peacock eye cichlids. They got the name velvet cichlid due tot he fact that their scales are small and sometimes give the appearance of the fish being covered in velvet. German aquarists called them peacock eye cichlids due to the ocelli the fish sport. When I first started in the hobby, many people were still referring to them as velvet cichlids.


There are two possible origins for the name Oscar. In 1936, E.W. Clarke mentioned the names of his two Oscars, Lena and Oscar in an article for The Aquarium. Later,in 1949, Gene Wolfsheimer mentioned that aquarists in California were referring to these fish as Oscars in an article for The Aquarium Journal. (Wayne Leibel, Aquarium USA Annual 2001)


Oscars originate in the Amazon basin where they populate still or very slow moving waters. There they feed on aquatic insects, flying insects that have the misfortune of hitting the water, crustaceans, and occasionally fish. They attain a size of anywhere from 10 inches to 14 inches or more for an exceptionally large male.


Now, for keeping Oscars at home. I will lay out their requirements and then address a few myths about them.


Tank size. Oscars are large heavy-bodied fish requiring a good amount of territory and good water volume to keep from having the tank fouled too quickly. Given this, the minimum size tank a single Oscar should be housed in is a 55 gallon. A standard 55 is only 12 inches or so from front to back, so if your Oscar is a large male, even that may not be enough to afford a comfortable turn radius. For that reason, some people suggest a minimum of a 75. The 55 should do fine though. A pair would require at least a 75. These are big fish, and require big tanks.


Water parameters. Oscars are relatively easy on this score. They can do OK in a wide range, but my feeling is that you should provide them with as close to natural conditions as possible. pH should be between 6.5 and 7. Medium hardness, up to 10 DKH or so. Temp between 78-82.


Filtration. As mentioned, Oscars are messy fish, and they require good filtration to do well. But at the same time, they do not appreciate the equivalent of a raging river in their tanks. Remember, they come from slow moving water. On a tank with a single Oscar, a good canister filter such as a Magnum 350, or one of the larger Eheims in conjunction with a large HOB type like an Emperor 400 should do good. Whatever you use, good mechanical and biological filtration are an absolute must for an Oscar tank. You can not cut corners here. An oft-quoted rule of thumb is 10 times the water volume in water flow. That is a good starting point, but as with all such rules, it is ONLY a guideline.


Water changes. Here is another thing that can NOT be neglected if you want a healthy Oscar. No matter how well your tank is filtered, the filters are not going to keep the water free of the dissolved solids that water changes remove. While this is true of any aquarium, it is especially so in an Oscar tank. At the minimum you should do 50% once a week, with thorough gravel vacuuming. That is a MINIMUM. If you don’t follow that, you will run into problems down the road.


Feeding. Oscars need a varied diet to do well. Earthworms, crickets, chopped shrimp, krill, crayfish all should supplement a good quality pellet food. Add to that brine shrimp, bloodworms and black worms for juvenile fish up to about 4 inches or so. Notice the lack of feeder fish on that list? I will address that in a moment.


Decor. Having decorations in an Oscar tank can be difficult to say the least. Oscars dig. They dig A LOT. And they move things. If they don’t like where the pick up tube for the filter is, or do not like your placement of the heater, the will do their level best to correct your obvious lack of interior decorating skills. Plants are right out. Unless you use plastics, and then they are most likely going to be Oscar toys anyway. Driftwood and rocks are OK, so long as they are large enough that the fish can’t move them...far. I once had a pair that would move a large rock I had in the tank every night. The rock weighed a good 7 or 8 pounds. The two of them would team up and push the rock to the other side of the tank. I kept putting it back. It gave the fish something to do and it was entertaining to watch.


Health care and diseases. If you follow the requirements I laid out, you will likely not run into any problems. Good diet and proper maintenance prevent most if not all problems in any tank, and this applies to Oscars as well. But, if you are unfortunate enough to have a problem, it will usually be one of these.


Ich. Ich is a problem in ALL tanks, and a subject that has been covered in many books and articles. I will simply say that using a good ich med like Quick cure or a salt treatment will take care of the outbreak. However, you will need to address the reason for it. Ich is constantly in the water, and the fish only succumbs if it is stressed or another fish is introduced that has Ich. Like a sick feeder. Be sure your Oscar has a large enough tank, you are doing sufficient water changes, and if you MUST feed feeders, be sure to quarantine them before using them.


Fin rot, cloudy eye. These are both problems directly connected to water quality. Regardless of the fact that bacteria or fungus are causing the problem, it likely would not have occurred if the water quality in the tank were maintained. Again, salt treatment works well for this problem. And again, be sure to address the water quality issue.


Hole In The Head (HITH) This is a common problem with Oscars. For brevity’s sake, I will simply refer you to the article I wrote on this disease. Hole in the head disease in Oscars.


Myths. Myths abound when it comes to these fish. Here are some of the more popular ones.


Oscars are piscivores. This one is actually understandable. In his book, Jumbo Fishes for the large aquarium, Dr. Axelrod states "...but essentially they are piscivorous...". This is an understandable assumption given their structure and size, but it’s not true. Gut studies indicate that only 19% of the non-plant contents were fish. (Lowe-McConnell 1991). In other words, if a fish happens to be near and the Oscar can nab it, he will. But that is not their preferred prey. Insects are.


Oscars are a beginner’s fish. Not at all true. They ARE easy to keep, but given their space requirements and the heavy maintenance needed to keep them healthy, they can not be considered a good beginner’s fish.


Oscars are aggressive. Again, not totally true. Yes, if two Oscars are in a tank that is too small for them there WILL be a fight for territory. And mating can indeed be a bit rough. But that can be said about a lot of fish. For their size, Oscars are actually pretty much an easy-going fish.


Oscars will not outgrow their tanks. Now, this is one that is said about all fish by misinformed people, but it is decidedly untrue about Oscars. Oscars are fast growing fish, and they will do that growing no matter what size tank they are in. Period. I have seen any number of deformed Oscars that were that way because someone thought a 29 gallon tank was good enough.


I sincerely hope this article can help you to avoid the plight of our aforementioned hobbyist. These fish are well worth the effort and space required to keep them.


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