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FAQs on Oscar Disease by Category: Environmental, Nutritional, Social, Infectious, Parasitic, Genetic, Treatments,

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Keeping Your Oscar/s Healthy!
Notes on preventing illness in Neotropical Cichlids



By Bob Fenner



               Like most all aquarists, I came “into the life” via keeping goldfish in way too small containers, the usual mix of guppies, platies, mollies and swordtail livebearers, general cichlids into “exotic” African species, thence to saltwater, reefs… Yes, including keeping the lovable Oscar, Astronotus ocellatus. Most folks who don’t know much about aquariums remark that they prefer companion animals like dogs, cats, birds… among other reasons because they’re vocal; able to communicate if/when there’s something amiss. Well, Oscars are able to speak plainly and loudly if you’ll but listen!

               In the course of the daily building of our website, WetWebMedia.com, I am given to help answering, spiffing up, and parsing our accumulated “Frequently Asked Queries”… On the occasion that they general FAQs files get too big (as defined by taking more than a minute to download at a nominal 56.6 Kbytes/second), they are split up, another file created. The aggregate “Oscar Health/Disease” files have grown to such an extent that I am taking this opportunity to syncretize/synthesize our collective input into this article… for all the Oscars in captivity (and their owners/caregivers).

               Yes, the Neotropical Cichlid we call the Oscar or Velvet Cichlid is a great aquatic pet… hardy, tolerant of a wide variety of water conditions, intelligent, beautiful in its various color and finnage availabilities, and communicative! But too many of these gregarious fish fall prey to simple hobbyist neglect and lack of understanding of basic needs. Here we will address these categorically.

Health Issues: By Causes

               As with most all fish-keeping, this is the single largest source of trouble… Unsuitable environmental issues account for the bulk of troubles and losses. Oscars are an incredibly tough, aquarium-suitable species, but they do need space, clean, aerated water with a dearth of accumulated metabolites, and suitable tankmates.

               How much room is enough? Too many people start off well-intentioned; as in the road to wherever is paved w/ good intentions; stocking their Oscar/s in too small volumes, intending to upgrade “someday” when their fish are bigger. Like a good boy scout, “Be Prepared”… a single adult Oscar needs at least fifty five-sixty gallons of uncrowded space to live well and long. Two specimens require a hundred-plus gallons. Restricting yours to smaller spaces will shorten their lives and cause them psychological damage.

               Related to aquarium/system volume, these fish need over-sized filtration (redundancy a good idea) and circulation. Do consider having more than one jumbo outside power filter, canister, and aerators in their tank; along with good-sized (25-30%) weekly water changes and gravel-vacuuming to dilute wastes. In tank filters, including undergravel, are not a good idea, as this fish has a distinct tendency to rearrange its environment, including moving the gravel about. While on this topic of environment issues/precautions I’ll mention using a heater guard in their tanks as well to prevent breakage.

               How to monitor waste build-up in an Oscar’s system? In an established, not over or mis-fed system, there should be no, as in zero Ammonia or Nitrite presence; and less than 20 ppm of Nitrate at any time. Many co-causes of Oscar disease and mortality are indirectly attributable to these simple water quality measures gone unattended. The olde saw: “When/where in doubt, change water” definitely holds for these gentle giants.

               Issues w/ incompatible tankmates abound. Giant Plecostomus species can work them woe, sucking on their sides, opening the skin to infection, and all-too-often being kept w/ other Neotropical species, even smaller Jack Dempseys, Convicts… results in Oscar’s losing their health. And don’t be so sure re placing “pairs” or numbers of Oscars together either. They can and do turn on each other, especially when crowded.


Nutritional Diseases:

               Without a doubt, the second most common contributor to the health, and its antithesis, disease of Oscars (and most captive aquatic life) is related to foods, feeding and nutrition. The major failings of aquarists here fall into two major categories. Feeding non-nutritious foods, and secondly, offering foods that outright damage Astronotus health and introduce diseases.

               Flake foods are of little to no use to Oscars unless the specimens are very small. Alternatively good-brand pellets (e.g. Hikari, New Life Spectrum) can be a steady diet for the life of these cichlids. Beware of brine shrimp based foods as staples, land-based animal (beef heart, liver) that are too fatty and hard to digest. Large shrimp and crayfish are too concentrated with Thiaminase and lead to various internal disorders. Frozen/defrosted marine-based fishes, whole or in parts are excellent adjuncts to a good pellet diet.

               Goldfish, other minnows are Thiaminase sources as well as being great vectors of parasitic and infectious disease. Stay away from these “foods” period. I have used comet/”feeder” goldfishes for fish disease demonstrations for decades; they never disappoint. Expensive, diseased and invoking violent behavior, they should NOT be sold, or used as food.

               Hole in the head disease, aka lateral line/neuromast destruction syndrome, is a matter of poor nutrition coupled with diminished water quality; and is quite common in Oscars. The pitting can be reversed if attended to readily, and it’s never a poor idea to supplement foods by soaking them in preparations of vitamins and HUFAs.

               Oscars should be fed twice a day, but never to satiation. Overfeeding pollutes the water and shortens their life-spans.


Social/Psychological Diseases:

               Many Oscars are killed by their erstwhile tankmates, directly by beating/biting… and less directly, by bullying. Providing an overly-large volume system would/could greatly decrease these incidents, but it pays to observe your aquatic charges carefully for signs that all are not getting along. I have seen large species of Plecostomus kill Oscars, other Neotropical cichlids do so, though considerably smaller in size; even true goramis may pick on them to death.

               The best situation is to buy all specimens you intend to keep and have them grow up together. Second best is to provide a barrier wall twixt established and newly introduced fishes. And, as stated over and over, more space makes for better neighbors. Be leery of direct introduction of any new specimens being placed in an established system. Moving around the décor may help, but remember that social dynamic situations can and do change rapidly in these systems.


Infectious Diseases:

               Oscars are susceptible to bacterial, fungal and viral troubles; and these are almost always secondary in origin, brought on by poor water quality, social issues, and other sources of stress. I have yet to find an incidence where these “infections” could not be cured by simple improvement of the environment and nutrition… without the use of medications or phony “fixes”. Should you suspect one of these agents, first and foremost look to the environment. When/where in doubt, check water quality and execute a good sized water change.


Parasitic Diseases:

               Though tougher by far than some sort of average freshwater fish, Oscars do get White Spot and other Protozoan infestations; an assortment of worms and flukes, even the Branchiuran crustacean called Anchor Worm (from feeders).

               For White Spot/Ich, Velvet and other single-celled parasites, commercial preparations including Malachite Green along w/ elevated temperature, will affect a cure. Anthelminthics like Praziquantel work fine for all types of worm diseases, and commercial cures containing organophosphates easily defeat crustacean parasites.

               Of course, the best route is to avoid introducing these pests by careful livestock selection and avoidance of vectors.


Genetic Diseases:

               As with Disney's “Nemo”, there are Oscars borne w/ diminished pectoral fins, one’s with single eyes, fin deformities and various internal genetic errors. If these don’t offend you, and the animal lives and grows to moderate size, it is likely to continue just fine.


About Treating Diseases:

               I’ll reiterate (“journey again”) regarding disease in this species. Almost all problems are iatrogenic… that is, caused by, and able to be avoided by the hobbyist. That’s you. If your Oscar appears ill, look to the environment first, nutrition second, for likely cause. IF you find yourself wanting to treat the symptoms, still check your water quality, affect water changes ahead of medicating. Many more animals are killed rather than cured by such treatments.



               Oscar cichlids are supremely adaptable and hardy, but do require some basics: Large enough space, clean/consistent water, decent foods, and a lack of exposure to disease causing organisms. Being careful at picking out initially healthy specimens and providing these basics will get you long-term happy and healthy aqua-dogs. Should yours show signs of disease, don’t hesitate; do be pro-active in determining root cause/s and remedying them in short fashion.   


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