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Oscar Fish Information Answering some oscar fish questions. By Paul V. Loiselle Q. I have a 50-gallon tank to which I have added two 3-inch oscars. I think they will have adequate room to grow. The tank is equipped with two powerheads and a power filter on the back. What other types of fish can I put in with my oscars that they won't eat? Can they be bred? They were sold to me under the name tiger oscar. Anything you can tell about them would be much appreciated. A. The 50-gallon tank you describe is adequate for your oscars at their present size. Oscars, of course, can grow significantly — up to 10 inches in length — and even a 50-gallon tank will be too small for two adult fish at that size. If you are serious about keeping these fish on a long-term basis, it would be a good idea to give serious consideration to providing them with more living space at some point down the road, keeping in mind that oscars can grow larger rather more quickly than you might assume. Right now, there is no reason why you can't keep them with a fairly wide selection of other fish. Tinfoil barbs, for example, are too large and fast to be considered as possible food items by oscars, and they provide a certain amount of dither activity for the oscars that will keep them active and out in the open. Dither fish are an important aspect of many cichlid setups. The reason is that the presence of other fish, particularly schooling fish, swimming about is a sign that all is well, thus encouraging the cichlids to stay in the open rather than hide. You could also try keeping them with some of the less aggressive South American cichlids, such as green severums, blue acaras or juriparis. These fish are, again, too large for the oscars to consider as a potential meal and are not so aggressive that they will cause the oscars trouble at any time later. I strongly recommend against keeping oscars with any of the larger Central American cichlids. These fish tend to be much more aggressive than the oscars and will often give them a hard time. There is no reason why you cannot breed your oscars, provided that you actually have a pair. This is not the easiest thing in the world to determine. There are no really reliable color differences that allow you to tell male from female. When your oscars are a bit larger, between 4 and 5 inches, you can remove them from the aquarium, one at a time, turn them over and examine the shape of the genital papillae. This structure comes to a fine point in males and tends to be blunt and wide-mouthed in females. There is a useful diagram showing these differences in my book, The Cichlid Aquarium (Tetra Press), that you might like to consult. Oscars are not the easiest neotropical cichlids to breed even if you have the good fortune to own a male and a female. When they do spawn, they are very prolific. Consequently, you will find yourself having several thousand voracious young to feed. Give some serious thought to both housing and growing the young, as well as disposing of them before committing yourself to the breeding project. In any event, I see no reason why you can't look forward to many months of pleasure as you watch your oscars grow and develop the distinctive personality that these highly intelligent cichlids often show toward their owners. Just remember that you should be prepared to provide them with larger qurters as they grow. Keeping the Water Clean Q. I have kept oscars for the past 10 years and never before have I run into a problem as persistent as the one I now face. My 100-gallon aquarium, which houses three 8-inch oscars and three 4-inch oscars, has become a source of great problems for me. The gravel becomes fouled in a matter of three or four weeks, which in turn raises the nitrite level to the danger point. I don't feed these fish any more than they can consume in a matter of minutes. Could the cichlid pellets I am providing be the cause of the problem? I know that the oscars are extremely messy eaters, but I also know that I am not overfeeding them. The filtration on the tank consists of a canister filter and an outside power filter that is rated for a 100-gallon tank. I also have a diatomaceous earth filter that usually runs three or four days a week. I believe that the tank is more than adequately filtered. I change 20 gallons of water every week, but that does not seem to ease the severity of the problem. My tap water comes directly from a stream that runs close to the house and does not undergo any chemical alteration. I have two filters on the line coming into the house to remove dirt and sediment. The pH of the water is 7.4 and the nitrite reading right out of the tap is less than 0.1 milligram per liter. I live in a rather rural area and thus my resources, such as stores and other hobbyists, are severely limited. I have yet to find any other people in this area who are interested in keeping fish. I have read your book, The Cichlid Aquarium, and found it very helpful. However, it does not address this particular problem. Could I simply be keeping too many fish in this tank? What am I doing wrong? A. Oscars are indeed messy eaters, and there is simply no way to keep food and waste products from fouling the gravel of the tank in which they live. You obviously are on the right track regarding husbandry. The water changes are exactly what I would recommend under the circumstances. However, as valuable as frequent partial water changes are to any aquarium setup, just changing the water is not going to purge the gravel of these wastes. I believe the easiest way to get around the problem is to invest in a device known as the Python No-Spill Clean and Fill. This apparatus is a combination water changer and gravel cleaner, and will allow you to clean the gravel as you make your regular water changes. Once you have one of these useful appliances in hand, I think you'll find that the problem of maintaining suitable water quality for your oscars will be much simpler. It does not seem to me that you are overfeeding. I have used pelletized foods for many years to feed a wide range of cichlids without encountering a problem. This sounds to me like a typical oscar problem, and as long as you want to keep these fish you are just going to have to live with it. Investing in an apparatus that allows you to purge the gravel at the same time you change the water is probably the simplest way to solve your problem. Vision Problems Q. I recently purchased a tiger oscar at a local pet store. Upon bringing my new oscar home, I noticed his eyes had something wrong with them. A strange orange bubble covers the pupil of the left eye, and appears to have caused loss of sight in this eye. A cloudy dot is evident on the surface of the right eye, but the fish still seems to have vision in it. What do you suggest I do? A. The bubble-like structure you describe in your fish's left eye is probably the result of damage inflicted during the course of a fight. The eyes are vulnerable, which may explain why so many fish species target them in serious bouts of aggression. I would suggest that your oscar can still perceive light and movement through the damaged eye, but resolution of detail is no longer possible. Regrettably, such eye damage is irreversible. Cichlids with such injuries would be unlikely to survive in nature, where predators lurk, but appear to manage very well in captivity. While clearly not a show-quality specimen, your oscar should still make a satisfactory pet and could even be used as breeding stock if care were taken to find a compatible partner. Milky or cloudy patches on the surface of the eye are usually the result of environmental trauma. Damage due to net abrasion, pH shock or poor water quality usually account for this condition. Once the source of stress is removed, the eye should recover its customary clarity rapidly. Supportive treatment in the form of a vitamin B12-based tonic can do no harm and seems to accelerate regeneration. Such mechanical damage carries with it a risk of bacterial infection. In fish so afflicted, the cloudiness will cover the entire surface of the eye, whose surface may develop a flannel-like appearance. Any furan-based antibiotic used according to the manufacturer's instructions will treat such "eye fungus" effectively.
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