Aquarium

Oscar Fish: Types, Feeding, Reproduction, and Care

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By Milthon Lujan

Oscar fish (Astronotus ocellatus). Source: Jón Helgi Jónsson (Amything)
Oscar fish (Astronotus ocellatus). Source: Jón Helgi Jónsson (Amything)

Have you ever seen a fish with vibrant colors and a surprising personality? If so, you may have encountered the Oscar fish (Astronotus ocellatus). These captivating cichlids are popular among aquarists for their beauty, behavior, and intelligence, as they can recognize their owner. But before bringing one home, it is essential to understand their needs and requirements.

Apart from their significance in the ornamental industry, the Oscar fish is bred using aquaculture techniques for the production of meat for human consumption in countries like Brazil and Peru. Even though its aquaculture is still in its early stages, its hardiness and market demand augur great potential for this activity.

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This article will guide you through everything you need to know about the Oscar fish (Astronotus ocellatus), from its origin and types to its care, diet, and breeding. Whether you are an experienced aquarist or a beginner looking to venture into the fascinating world of Oscar fish, this article will provide you with the necessary knowledge to ensure a prosperous and satisfying experience.

Origin and Habitat of the Oscar Fish

The Oscar fish, also known as Astronotus ocellatus, is a freshwater cichlid native to South America. It is mainly found in the Amazon basin, in countries such as Brazil, Peru, and Colombia. It prefers warm and calm waters, with abundant vegetation and submerged logs.

Oscar fish are resilient and have adapted to a wide range of water conditions, making them suitable for aquariums; however, due to unwanted introductions, wild populations have developed in China, Australia, and the USA.

Physical Characteristics

The Oscar fish is a large fish, with a robust and elongated body. It can reach up to 30 cm in length, weigh up to 1.5 kg, and live between 10 and 15 years depending on the care provided. Its coloration varies, but it generally has an orange background with dark spots and a black ocellus on the caudal fin.

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The wild type of Astronotus ocellatus has a black body accompanied by bright orange/red stripes and black eyes, while the albino type has a white body accompanied by bright orange/red stripes and pink/orange eyes. Juveniles have wavy bands of white and orange stripes and spotted heads.

Male Oscar fish are usually larger and more colorful than females; however, there is no clear sexual differentiation at first glance.

Taxonomy of Oscar Fish

Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Perciformes
Family: Cichlidae
Genus: Astronotus
Species: A. ocellatus
Spanish Name: Pez Oscar, acarahuazú, copaneca.
English Name: Oscar Fish, Tiger Oscar, oscar cichlid, Marble Cichlid, or Velvet Cichlid.

Types of Oscar Fish

Oscar fish are available in a variety of color forms, each with its unique charm and appeal. From classic Tiger Oscars to stunning albino varieties, here are some of the most popular types of Oscar fish available to aquarists.

Tiger Oscar

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The Tiger Oscar is perhaps the most iconic and recognizable type of Oscar fish. Known for its bold black stripes and vibrant orange, red, and yellow colors, the Tiger Oscar is a favorite among aquarists for its striking appearance and attractive personality.

Red Oscar fish. Source: Lukaso40
Tiger Oscar fish. Source: Lukaso40

Albino Oscar

The Albino Oscar is an impressive variety known for its creamy white body and bright red eyes. With its unique coloration and playful behavior, Albino Oscars are a captivating addition to any freshwater aquarium.

Albino Oscar fish. Source: Citron
Albino Oscar fish. Source: Citron

Red Oscar

The Red Oscar, as its name suggests, is characterized by its vibrant red color. With its intense hues and striking markings, Red Oscars are sure to stand out in any aquarium.

Red Oscar fish. Source: Mazapura
Red Oscar fish. Source: Mazapura

Wild Type Oscar

The Wild Type Oscar displays a more subdued coloration, with shades of green, brown, and black. While not as flashy as some of the other varieties, Wild Type Oscars have a natural beauty and elegance that appeal to many aquarists.

Oscar Fish Care

Aquarium Size

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Oscars require a spacious aquarium. For a single fish, a minimum of 200 liters (55 gallons) is recommended, while for a pair, 300 liters (75 gallons or more) is ideal. The tank should be equipped with a sturdy lid to prevent escapes, as Oscar fish are known to be excellent jumpers.

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On the other hand, research by Dopeikar et al., (2021) and Dopeikar et al., (2024) reports that the use of red-colored tanks is more effective than other colors for breeding Astronotus ocellatus, in terms of growth, hematological, biochemical, and stress factors, which may be due to a greater and better physiological adaptation of the fish to this color.

Water Parameters

As mentioned earlier, Oscar fish are resilient to variations in water quality. The following table presents the basic parameters that the water should have for proper Oscar fish breeding.

Water ParameterOptimal Range
Water Temperature72-78°F (22-28°C)
pH6,0-8,0
Hardness5-15 dGH

Filtration and Oxygenation

A powerful filtration system is essential for maintaining water quality. Ensure adequate oxygenation through diffuser stones or electric heads.

Decorations

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The aquarium where you will raise your Oscar fish should have a series of hiding spots and areas with rocks, driftwood, and plants.

Feeding

The Oscar fish is omnivorous and can eat a wide variety of foods, such as small fish, shrimp, worms, pellets, and flakes. It is important to offer a varied and balanced diet to keep it healthy.

Types of Food

Offer a varied diet of high-quality cichlid pellets, live or frozen foods such as brine shrimp and bloodworms, and occasional treats like chopped vegetables. Khade et al., (2018) recommend using foods with at least 50% crude protein in Oscar fish juvenile diets.

A protein-rich diet not only promotes faster growth of Oscar fish but also helps fish cope with stress from confinement and increases survival (Zare et al., 2024). Likewise, Castro-Castellón et al., (2020) recommends the inclusion of carotenoid pigments in fish diets.

The results of Mohammadiazarm et al., (2021) recommend including powdered spirulina at a level of 55 g/kg of diet as a functional natural food additive to improve the performance of Oscar fish (Astronotus ocellatus). In the same vein, Hoseinifar et al., (2016) recommends the inclusion of xyloligosaccharide (XOS) in the diet to promote the growth and intestinal microbiota of A. ocellatus; while Hasaninia et al., (2022) investigated the effect of Lactococcus lactis and Bacillus subtilis in the diet on immune responses, intestinal microbiota, and pathogen resistance of Oscar fish, Astronotus ocellatus, reporting good results.

Saghaei et al., (2015) evaluated the effect of different levels of garlic (Allium sativum) on the growth and body composition of Oscar fish (Astronotus ocellatus), and concluded that 10 g kg-1 of powdered garlic has a good effect on the growth and body composition of the fish. Finally, some scientific articles also recommend the use of probiotics, prebiotics, and symbiotics in ornamental fish farming.

Feeding Frequency

In general, it is recommended to feed adult Oscars twice a day. However, some factors can influence the ideal frequency:

If the Oscar fish is:

  • Small (less than 10 cm): Feed three times a day with small amounts.
  • Large (more than 15 cm): Feed once a day or even every two days.
  • In cold water (less than 24°C): Feed once a day.
  • In warm water (more than 28°C): Feed twice a day.
  • Eating live food: Feed once a day.
  • Eating frozen or pelleted food: Feed twice a day.
  • Very active: Feed two or three times a day.
  • Less active: Feed once a day.
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Signs an Oscar fish needs to eat:

  • Swims around the water surface looking for food.
  • Opens its mouth when it sees food.
  • Appears thin or emaciated.

Signs an Oscar fish is overeating:

  • Leaves uneaten food.
  • Defecates frequently.
  • Its belly swells.

The ideal feeding frequency for adult Oscars varies depending on the size of the fish, water temperature, type of food, and activity level. It is recommended to feed them twice a day, but this frequency can be adjusted according to individual needs.

How do Oscar fish reproduce?

The reproduction of Oscar fish can be a rewarding experience for aquarium enthusiasts. Before attempting to breed Oscars, it’s important to ensure you have a compatible pair. Oscars are known to form monogamous bonds and can become territorial during the breeding process.

It’s important to note that Oscars reach sexual maturity at one year of age, and there is no clear sexual dimorphism among Oscar fish; therefore, the most practical way is to wait for pairs to form. However, if you’re into research and have experience in fish breeding, you can follow the protocol described by Mansur et al., (2021) on surgical techniques applied via videoceloscopy and gonadal biopsy for A. ocellatus sexing procedures.

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To encourage breeding, provide a separate breeding tank with appropriate conditions, such as slightly warmer water temperature and increased oxygenation. The female Oscar fish will lay eggs (between 500 and 1000) on a flat surface, such as a clean rock or piece of wood. The male will then fertilize the eggs and guard the nest until they hatch.

The eggs of Astronotus ocellatus are demersal, adhesive, and fragile to the touch, slightly oval-shaped (Paes et al., 2012). Fertilized eggs have a yellowish color. Larvae hatch between 46 and 58 hours at an average temperature of 27°C.

The parents will continue to protect and care for the fry. After a few days, the fry will begin to swim freely and can be fed a diet of brine shrimp (Artemia) or finely crushed flakes. It’s important to separate the fry from adult Oscars to prevent them from being eaten.

Common Diseases

Oscar fish are susceptible to some common diseases, such as ich, hole-in-the-head disease, and fin rot. It’s important to regularly observe the fish for any signs of illness and treat it promptly.

Regular observation and immediate action are crucial for addressing any signs of illness in Oscar fish. If you notice abnormal behavior, changes in appetite, or physical symptoms, consult a veterinarian or experienced fish breeder for proper diagnosis and treatment.

Hole-in-the-Head Disease

A common health issue in Oscar fish is hole-in-the-head disease, also known as hexamita. This condition is characterized by the development of open sores or holes in the fish’s head. It can be caused by poor water quality, stress, or lack of essential nutrients. To prevent hole-in-the-head disease, maintain a clean and well-maintained tank, provide a balanced diet, and avoid overcrowding.

Peyghan et al., (2010) treated an Oscar fish affected by hole-in-the-head disease with a long-duration bath of 6 mg/l metronidazole and after 24 hours, with 0.2 ppm malachite green mixed with 0.15 ppm formalin; they also fed the fish with a balanced diet enriched with vitamins through gastric tube for several days. The fish recovered completely within 10 days.

Exophthalmia associated with holes in the frontal region of an Oscar fish. Source: Peyghan et al., (2010).
Exophthalmia associated with holes in the frontal region of an Oscar fish. Source: Peyghan et al., (2010).

Compatibility with Other Fish

The Oscar fish is intelligent and curious. It is very active and territorial, especially during the breeding season. It can be aggressive towards other fish, especially those of the same species. However, it can also be a very social fish and form bonds with its tank mates.

Some suitable tank mates for Oscar fish include large cichlids, such as Jack Dempseys, Firemouths, or Severums. Species of catfish like Plecos or larger Corydoras can also coexist peacefully with Oscars. However, it is important to monitor their behavior and be prepared to separate any aggressive or incompatible tank mates.

Tips for Keeping Oscar Fish Healthy

To ensure the well-being of your Oscar fish, consider the following tips:

  • Provide ample space: Oscars require plenty of space to swim and explore. A larger tank will help reduce stress and promote overall health.
  • Maintain water quality: Test water parameters periodically and perform partial water changes to keep the tank clean and water quality optimal.
  • Offer a varied diet: Provide a balanced diet that includes both protein-rich foods and plant-based options to meet their nutritional needs.
  • Stimulate their environment: Add decorations, hiding spots, and toys to keep your Oscars entertained and engaged.
  • Monitor behavior and health: Periodically observe your Oscars for any signs of illness or abnormal behavior. Take immediate action if any issues arise.
  • Avoid aggressive tank mates: Choose compatible tank mates that are similar in size and temperament to avoid conflicts and stress.

Where to Buy Oscar Fish and Supplies

Oscar fish can be found at various pet stores, both online and offline. It’s important to choose a reputable supplier that provides healthy, well-cared-for fish. Look for stores with knowledgeable staff and a wide range of fishing supplies.

When purchasing Oscar fish, consider their size, color, and overall health. Healthy Oscars should have bright colors, clear eyes, and active behavior. Ensure the store has proper acclimation procedures to minimize stress during transportation.

In addition to fish, you’ll also need to purchase the right supplies, such as a suitable tank, filtration system, heater, and decorations. Research the specific requirements of Oscar fish and invest in high-quality equipment to provide the best possible environment for your new aquatic beauties.

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Conclusion

The Oscar fish is a fascinating and attractive fish that can be a great addition to a freshwater aquarium. However, it’s important to note that it requires a large tank, specific care, and a varied diet. If you’re thinking of acquiring an Oscar fish, make sure you’re prepared to provide the care it needs.

On the other hand, if you’re thinking of breeding your Oscar fish in a community tank, you should consider compatible fish to avoid unwanted surprises. Also, make sure to continuously provide and monitor water quality to ensure the well-being of your fish and reduce the risk of disease.

References

Castro-Castellón, A. E., Castro-Mejía, G., Castro-Mejía, J., Monroy-Dosta, M. C., & Martínez-Meingüer, A. M. (2020). Determination of weight and length gain of Astronotus ocellatus (Agassiz, 1831) in a biofloc system with a pigment-rich diet. International Journal of Fisheries and Aquic Studies, 8, 200-204.

Dopeikar, H., Khoshkholgh, M., Qasemi, S. A., & Morshedi, V. (2021). The effect of tank color on growth index, hematological parameters and physiological responses of Oscar fish (Astronotus ocellatus Agassiz, 1831).

Dopeikar Hakimeh, Majidreza Khoshkholgh, Seyed Ahmad Ghasemi, Vahid Morshedi, “Effects of Background Color on Growth, Stress, Biochemical, Hematological, and Immunological Responses, and Expression of Growth-Related Genes in Oscar Fish (Astronotus ocellatus)“, Aquaculture Research, vol. 2024, Article ID 6957201, 10 pages, 2024. https://doi.org/10.1155/2024/6957201

Hasaninia, A., Roudari, H. V., Khara, H., Masouleh, A. S., & Ahmadnezhad, M. (2022). Effect of dietary Lactococcus lactis and Bacillus subtilis on the innate immunity, intestinal microbiota, histometrical indices, and resistance against Aeromonas hydrophila in Oscar, Astronotus ocellatus Agassiz, 1831. International Journal of Aquatic Biology, 10(6), 438-450.

Hoseinifar, S. H., Khalili, M., & Sun, Y. Z. (2016). Intestinal histomorphology, autochthonous microbiota and growth performance of the oscar (Astronotus ocellatus Agassiz, 1831) following dietary administration of xylooligosaccharide. Journal of Applied Ichthyology, 32(6), 1137-1141.

Khade, S. T., Lokhande, P. C., Sharangdhar, M. T., Kolekar, A. D., Gitte, M. J., Sharangdhar, S. T., … & Sharangdhar, A. M. (2018). Effect of different feeds on growth performance of juveniles Oscar, Astronotus ocellatus. Journal of Experimental Zoology India, 21(2).

Mansur, V. F. R., Melo, N., Di Chiacchio, I. M., de Lima Assis, I., Machado, G. J., Paiva, I. M., … & Murgas, L. D. S. (2021). Sex identification of the ornamental amazon fish Astronotus ocellatus by videoceloscopy and gonadal biopsy. Animal Reproduction Science, 230, 106780.

Mohammadiazarm, H., Maniat, M., Ghorbanijezeh, K., & Ghotbeddin, N. (2021). Effects of spirulina powder (Spirulina platensis) as a dietary additive on Oscar fish, Astronotus ocellatus: Assessing growth performance, body composition, digestive enzyme activity, immune‐biochemical parameters, blood indices and total pigmentation. Aquaculture nutrition, 27(1), 252-260.

Paes, M. D. C. F., Makino, L. C., Vasquez, L. A., Fernandes, J. B. K., & Nakaghi, L. S. O. (2012). Early development of Astronotus ocellatus under stereomicroscopy and scanning electron microscopy. Zygote, 20(3), 269-276.

Peyghan, R., Boloki, A., & GHORBANPOUR, M. (2010). Case report and treatment of hole in the head in oscar, Astronotus ocellatus.

Saghaei, A., Ghotbeddin, N., & Ghatrami, E. R. (2015). Evaluation of growth performance and body composition of Oscar fish (Astronotus ocellatus) in response to the consumption of dietary intake of garlic (Allium sativum). Aquaculture, Aquarium, Conservation & Legislation, 8(4), 485-490.

Wang, Q., Zhang, Y. S., Peng, Q. L., Wen, B., Gao, J. Z., & Chen, Z. Z. (2022). Distinct skin morphological and transcriptomic profiles between wild and albino Oscar Astronotus ocellatus. Comparative Biochemistry and Physiology Part D: Genomics and Proteomics, 41, 100944.

Zare, M., Esmaeili, N., Hosseini, H., Choupani, S. M. H., Akhavan, S., Salini, M., … & Stejskal, V. (2024). Do optimum dietary protein and early mild stress events prepare oscar (Astronotus ocellatus) for a stressful future?. Aquaculture Reports, 34, 101854.