Astronotus ocellatus, also known in the aquarium trade as the "Oscar", has been a popular aquarium fish for many years now. In fact, it is responsible for bringing many new aquarists into the hobby each year. The Oscar is playful and interesting, it is described by many as being the most "pet-like" fish you can keep in a glass box. I have personally kept Oscars for the past two years, and have derived a great deal of enjoyment from them.

In this paper, I will give a detailed description of the species; to include behavior, breeding, care requirements, and my own experiences with these fish. I will also include a short history of both the fish and modern aquarium equipment, in order to illustrate the amount of knowledge gained over the past decades about the species.

A. ocellatus is a member of the cichlid family. It's name derives from the Latin roots astron meaning star, and notus, meaning back, referring to the ocellated spot on both sides of the dorsal fin of the fish. It is this spot that distinguishes the species from A. crassipinnis. A. ocellatus, as a member of the Cichlid family, resides in Central and S. America. Other members of this family reside in Africa, the West Indies, Madagascar, Syria, and coastal India (Joseph Nelson, 1984). The Oscar distinguishes itself from other members of the cichlid family in several ways. Most notably is the absence of spiny scales, the Oscar has a smoother, leather or velvet like appearance. Indeed, the Oscar used to be known as the "Velvet Cichlid". The Oscar further separates itself from it's S. American counterparts by the anatomy of it's mouth and jaw region. In the Oscar, the lips and jawbones meet in the same angle as the mouth, rather than having the lower lip overlapping the upper. Other distinguishing characteristics of the species include a certain degree of "intelligence". More so than many other fish, Oscars appear to be keenly aware of their surrounding. When in captivity, they seem to recognize the person who feeds them.

As an aquarium fish, the Oscar has obviously been subjected to breeding programs designed to bring out certain color combinations. Common Oscar variations available include the Tiger Oscar, Albino Oscar, Common Oscar, Fantail Oscar, and Red Oscar. The Red Oscar is the most similar to the naturally occurring Oscar. It is a mostly greenish brown, with a large red streak on its underbelly. The Tiger Oscar maintains a similar greenish brown color, with red streaks throughout its body, the streaks running in a generally vertical direction. Common Oscars appear similar to both the Tiger and Red varieties, but generally have muted coloration, if at all. Albino Oscars are distinguished by a white body with a pinkish hue. Orange marbling, similar to a Tiger Oscar, occurs in the Albino variety. Finally, the Fantail Oscar is basically a Tiger Oscar with an elongated tail, in both directions. As a result of selective breeding, the captive born specimens available today, are far different than the naturally occurring varieties available.

Oscars are generally found in a variety of waters, temperatures, and pH levels. This, and it's behavior and coloration, have made it a big hit in the aquarium world. Ideal conditions for an Oscar would be a pH of 7.2, a temperature of 72-78 Fahrenheit, and an unlimited supply of food (more on that later). These parameters are a loose match to the Oscar's native environment. Of important note, is the degree of extremes an Oscar can survive. Many of it's native waters reach excesses of 90 Fahrenheit during the hotter months. Similarly, pH levels and Oxygen saturation may fluctuate greatly also.

In an aquarium, an Oscar is not the easiest fish to take care of. Oscars are omnivorous and piscivorus. They will pretty much eat anything. In the wild, they survive off of some aquatic plant matter, occasional insects, and other fish. Actual feeding behavior of a fish in the wild is somewhat difficult to determine, but in captivity, Oscars will make virtual pigs of themselves. Oscars have even been known to survive winters in lakes where they are not native, but have been released.

Oscars breed similarly to other cichlids. Unlike some of the African species, Oscars are NOT mouth breeders. They are egg layers. However, prior to egg laying, an elaborate mating ritual is carried out. As observed, it generally begins with a pair of Oscars "spending time together". Following this, the Oscars begin the more elaborate portion of their ritual. In a true, "survival of the fittest" sense, the Oscars will attempt to test the strength and hardiness of their potential mate. A pair of fish will generally lock lips, and have something of a tug of war. Each will attempt to dislodge the other one. At some point, one of the fish will dislodge. Either prior to the lip lock or just after (depending on the source) the Oscars will engage in some tail slapping and rubbing up against each other. At some point during this ritual, the two fish will have formed a "bond" and will remain together exclusively, until after the fry have been born.

Before continuing, it is important to discuss sex differentiation in Oscars. Visual identification of sex based on any external characteristics is very difficult. Various theories such as degrees of coloration and aggressiveness, the shape of the head, spots or color on the tail or gills, and others have all been tried, but with limited success. The only sure way to sex an Oscar is to look underneath the fish. To the rear of the fish's anus, is the sex organ. In the females, it is a small hole. In the male, it is a phallic appearing outcropping. However, these are not readily noticeable without magnification, and holding a fish upside down under a magnifying glass is difficult at best.

Following the mating ritual, the Oscars search for a place to lay and fertilize the eggs. A favorite is a flat rock. The rock is cleaned and leveled. Small rocks are picked up by mouth and carried away, and the surface is also cleaned by the mouth of the fish. Both the male and the female participate in this step. Once a suitable area has been setup, the female will lay the eggs, the male fertilizes them, and the parents begin the next cycle of guarding and caring for the eggs.

The majority of the Cichlids are excellent parents, and the Oscars are no exception. Once the eggs have been fertilized, the parents will take turns guarding the eggs. In addition to guarding, the fish will use it's tail fin to fan the eggs. This increases the water flow over the eggs, which provides for more viable fry. Occasionally, the parents may move the eggs from one location to another. Eggs which become infected with fungus may also be eaten by the parents. Eventually, the eggs will hatch, and the young will feed off of the remnants of the egg. Following that, the young will become free swimming. Once the young are free swimming , the parents duties continue. Parents will swim with the young in a school. Wayward young who leave the school are usually herded back or swallowed and "spit" back into the school. Eventually, the fry will grow and consume similar foods to the parents. Oscars do not secrete any special compounds for feeding, as do Discus and other cichlids. The fry are left to feed themselves.

Several problems in breeding Oscars do crop up. During mate selection, a lip lock between two fish can occasionally last for hours. Should one fish "fail" the test, the stronger fish may in fact kill the weaker fish. After the eggs have been fertilized, one of the parents may consume the eggs should a threat be perceived. This in turn leads to a second problem: The parent who ate the eggs or fry may then be attacked by the other parent and also killed. Although an excellent method to insure the viability of future generations, it does present problems to the breeder.

The next important topic is care and feeding of Oscars in the captive environment. In this section, I will present some of my personal experiences with keeping Oscars. I currently have a pair of Tiger Oscars that are approximately 10-11" long. I have raised them over the last 18 months or so from 1" babies.

It is impossible to create a perfect replica of a natural habitat in your living room aquarium, but it is easy to come very close. As mentioned previously, Oscars are voracious eaters. They are both omnivorous and piscivorus. This presents your first problem: feeding and cleaning up the mess. For feeding, Oscars will eat almost anything, so feeding is not too much of a problem, rather, overfeeding is the problem. A basic diet for an Oscar should include high amounts of protein and vegetable matter. I feed my Oscars a variety of prepared foods. On a weekly basis they also receive live food, in the form of Goldfish. Prepared foods should be looked at for protein content, a lack of moisture, and how badly they will foul the tank with detritus. After ingesting any form of food, Oscars will generally release bits of it through their gills. This is normal, although annoying. Also annoying are the rabbit sized feces the fish can produce. Obviously, due to the waste they produce, large tanks are in order. My pair live in a 55 gallon Glass tank, which is four feet long. This provides ample swimming space for exercise. Filtration is the other important issue for these fish. Mechanical filtration is imperative, and media must be changed/cleaned frequently. I change 25% of the tank's volume each week, and wash the filtration media at the same time.

Oscar behavior in the aquarium is fascinating to watch. As mentioned previously, Oscars are considered to be the most "pet-like" of fish. Oscars enjoy digging up gravel and moving small rocks to pass the time. Other activities they enjoy are chasing a bobbing ping-pong ball and playing tug-o-war with a piece of colored hose. Aside from their playful nature, Oscars are extremely territorial, particularly when they are ready to breed. When breeding, they will not tolerate other fish in the same area. In a four foot tank, this means that all other fish need to be removed, or the Oscars may fight with the others until a death occurs. Other than at breeding time, Oscars will generally tolerate other large fish. My Oscar's tankmates have included Green Terrors, Jack Dempseys, and Plecostomus. All of these have been tolerated, other than at breeding time. Surprisingly enough, despite their aggressive nature, Oscars seem to enjoy their owners petting them!

I purchased my pair of tiger Oscars in March, 1992. They were approximately 1" long. They lived in a 29 Gallon tank until they reached 6" long. They moved to their current home (55 Gallon) in February of 1993. Once they moved, they had a large growth spurt that took them to almost 8" in only a month. Over the last months, they have grown to their current size. Almost immediately after moving into the larger tank, my Oscars began to display signs of mating. Eggs were eventually laid on a flat rock, but no fry were ever produced. I do not know if I have a sterile male, or if I have 2 females. Since then, every 2 months, they will exhibit similar behaviors immediately after water changes in the tank. These have been very enjoyable fish to own, and I would agree that they have more personality than most fish.

The final area I would like to cover is the history of the Oscar and the history of recommended care procedures. Over the past decades, technology has increased to the point where reliable methods of fish-keeping have not only become more reliable and consistent, but also far more affordable. In addition, fish that were previously thought to be non-viable in an aquarium can be kept and grown to their full sizes and life expectancy. This is illustrated by comparison of several older aquarium atlases with newer ones.

Both the Inne's and Paysan guides list the Oscar as capable of growing to a maximum length of 8". These books are reprints of volumes published during the 1950's. Modern texts give the length at 12-14", depending on the book you choose. Older books give the listing as Cichlasoma ocellaris, while the newer texts use it's classification as Astronotus ocellaris. Finally, the older texts do not list the different varieties, but list the fish as a "Velvet Cichlid" and describe it as a "...sort of olive or suede leather." (Innes), or, "....black-brown to olive green...." (Paysan).

This paper is by no means a complete guide to the A. ocellatus species. I would like to conclude with a brief discussion on the equipment that has advanced aquarium science to the point where certain species once deemed impossible to keep are now possible. The whole issue boils down to water quality for the animals. Twenty years ago, an aquarium was kept with a power filter, which pulled water through tubes into a sump, filtered it through spun glass wool, and perhaps passed it through some activated charcoal. Water tests for ammonia, nitrites, nitrates, phosphates, and oxygen saturation were inadequate. Little was known about the nitrogen cycle or the various bacteria that converted toxic ammonia and nitrite into relatively harmless nitrates. An aquarium owner would depend on frequent and massive water changes to have clean water.

Over the years, we have improved the technology, making it easy and inexpensive to keep fish like the Oscar healthy, and allow them to grow and live to their full potential. For example, on the back of my Oscar's tank are two power filters. Each one filters 280 gallons per hour. Water is pulled from the tank, passed through polyester filter floss, activated carbon, and sprayed across a biological medium that aids in the growth of denitrifying bacteria. I have a heater that is submersible and accurate to tenths of a degree. I no longer have to "age" water, instead, I add a few drops of a compound that removes impurities before I refill the tank. Much of the success of the captive breeding and raising of fish can be attributed to the technology available today.

This article is a summary of information gleaned from various sources, my own experiences, and the experiences of other aquarists. It is my hope that it has given a solid description of Astronotus ocellatus, as well as methods and equipment necessary for success with this particular cichlid.

Since writing this article, my Oscars have grown only slightly. In September of 1996, these fish were moved into a 180 Gallon tank, where they still reside with a pair of Albino Tigers, a Pair of Jack Dempsey, a big Pleco, and two Green Terrors. Their health is still excellent, although they have both begun to exhibit that wrinkled, old look common to older fish. Also, their wounds don't heal as quickly as they used to (good old mating rituals), and they are not as quick to anger.