Top of the Food Chain: Feeding Oscars in the Home Aquarium

Author: Brian M. Scott

Oscars Astronotus spp. are some of the most popular and commonly kept fish in the aquarium hobby. In this installment of “Top of the Food Chain” I will rediscover my roots, so to speak, and pass along some useful information that I have gathered on successfully maintaining oscars in home aquaria.

Introduction

Most hobbyists have at least heard of oscars at some point in their fishkeeping careers, and many have kept them in home aquariums. After all, who can resist those big bug eyes and that incredible dog-like personality? Well, not many, and rightfully so. Oscars are amazing fish and exhibit some of the most unique and fascinating behavioral and husbandry traits of any commonly available freshwater aquarium species. This month I’d like to focus on passing along snippets of information that I have gathered on the proper diet and feeding of oscars in aquariums. So let’s jump right in!

Diet in Nature

Oscars are native to tropical and subtropical South America. Throughout their range wild oscars primarily consume meaty foods (mostly small whole fishes), while much of the remainder of their diet consists of live insects and insect larvae. It’s hard to break down the actual percentages of food types consumed, but it’s probably safe to say that live fishes and insects constitute approximately 90 percent of the overall diet of wild oscars.

Even though live fishes and insects make up the bulk of a wild oscar’s diet, there are other items that are taken as well. Fruits, nuts, shrimps, and snails are noted fare, with the fruits and nuts being consumed somewhat on a seasonal basis. Additionally, some authors have reported oscars being sighted around dead animals lying in the water. It is uncertain, however, if these fish were feasting on the actual dead animal or on the small fishes that such carrion attracts. I would say the latter theory is more widely accepted.

Diet in Aquaria

The diet of oscars maintained in aquariums is often drastically different compared to that of their wild counterparts. What I mean by this is that it’s rather uncommon for hobbyists maintaining oscars to feed them a variety of foods so as to replicate food selection in nature. Generally the two major foods being offered to aquarium-housed oscars are live feeder fishes and pellets formulated for large aquarium fishes.

It’s been my experience that oscars do best when offered a variety of foods, and while a diet that reflects that of a “natural” one is somewhat difficult for many hobbyists, it is extremely rewarding and surprisingly affordable to offer a diet that is at least close to that of a wild oscar.

Live Fishes

Many folks offer their oscars a diet made up almost exclusively of live feeder fishes. While live feeder fishes certainly do have their place on the menu for predatory fishes, they should never be the sole food offered unless such a diet is part of a larger goal (i.e., breeding, etc).

One of the biggest issues regarding the feeding of live fishes to any fish, oscars included, is the potential for disease transmission. Since many feeder fishes, especially goldfish, are raised in huge numbers by fish farmers, the risk of disease transmission is high. However, such a problem is less likely to occur these days compared to years past. The increased understanding of raising, transporting, and maintaining feeder fishes like goldfish and rosy red minnows has made them safer to use today than ever before. That said, I still do not advocate the use of live feeder fishes as an exclusive diet.

Insects & Worms

During the rainy season, when fish are scattered throughout the flooded forest, oscars tend to shift their diet toward insects and insect larvae. I have found insects like small crickets and mealworms to be fantastic foods for oscars. Be careful not to use insects that have been exposed to chemicals like fertilizers or insecticides. If you are uncertain of whether or not the crickets in your backyard have been poisoned, then simply do not use them. Your local pet shop will most likely be able to provide you with farm-raised crickets, mealworms, wax worms, and a wide array of other safe insects that are suitable as oscar food.

Fairly recently—at least within the past decade or so—several companies have began offering crickets and other insects in a prepared form, which are usually sold in small cans. These are perfect for use as oscar food, and many other species of fishes will benefit from their use as a dietary supplement as well.

Fruits, Nuts, and Veggies

Another food that oscars exploit during times of high water are the fruits (nuts) of several tropical trees. I have seen more than one oscar feed on peanuts or other somewhat soft nuts. Tropical nuts may not be available, and that’s fine. I would recommend feeding just one or two shelled nuts at a time. If the fish eats them, great, if not perhaps try again when you think he’s a bit hungrier—like in about five minutes!

I could probably write an entire article on just fruits and such for the oscar diet, but I wouldn’t want to get any nasty e-mails from my readers for wasting their time. However, let me just make mention of one particular type of veggie that I feel warrants special attention—frozen peas.

Frozen peas are a secret weapon in my arsenal of oscar foods. Without getting too deep into the science behind why I use these, let me tell you that they just simply work at enhancing the color and vigor of oscars in general. I always feed them frozen, too, which is not the norm when it comes to feeding my fishes frozen foods.

It’s very simple really; I just go to the supermarket and buy a small bag of frozen peas. Always keep them frozen, even until right before you offer them to your oscars. When the time comes for feeding, simply remove a few and rinse them under cold water then throw one at a time into the tank. If you have never offered your oscar this treat before, he may spit them out. Eventually, though, he will take them—and love them!

Prepared Foods

Prepared foods like pellets, tablets, crisps, flakes, and wafers are by far the most popular and easily found foods for feeding all aquarium fishes. Be smart, however, in the way you feed these foods to an oscar. Oscars are generally messy eaters, and the small particles that are produced by the fish’s chewing action are notorious for causing major water-fouling issues.

I have found that tablets, wafers, and pellets are more effective than crisps or flakes, even when an oscar is a juvenile. They tend to swallow tablets and pellets whole, with less gumming up, and wafers can easily be split in thirds and then offered to the oscar. When possible, try and offer prepared foods that are high in plant matter, as oscars tend to lack such materials in their diet. If these materials aren’t provided, then the fish’s colors can become faded and less striking over time, especially as it matures and grows into its adult coloration.

Try to offer a variety of prepared foods. It’s a good idea to have a half-dozen different kinds ready to supplement the oscar’s diet at any given time. This will make it very easy to vary their diet on a daily basis—even if it’s simply just varied in the type of pellets that are offered.

Fresh & Frozen Foods

Other foods that warrant mention for inclusion in the overall oscar diet are those foods that we call fresh and/or frozen. In most cases, when someone refers to such foods they are speaking of some form of seafood. Nearly all seafood is good for an oscar, as long as it’s offered in moderation, which is true for all types of foods, by the way—again, maintaining a varied diet is a key to success.

Fresh or frozen seafood like shrimps, scallops, clams, and squid make excellent additions to the fish’s diet and should be used often and in alternating form. One day shrimp, a few days later squid, and so on. Be creative but never overdo the seafood.

Other types of frozen foods like brine shrimp, bloodworms, mysis shrimp, and various similar formulas are not suitable for any but the smallest of oscars. Oscars are simply just too messy when it comes to feeding, and the small particles in such foods will do more harm than good for the fish in the long run. Stick to the big stuff, and simply cut it down to size as needed.

Quick Tips for Feeding Oscars

Oscars are gluttons, and they will consume as much food as they can possibly stuff in their bodies. Of course, and it should go without saying, that includes tankmates too. Since this article is primarily about the oscar’s diet and feeding, I won’t go into some of the other major husbandry factors that all hobbyists keeping these fish should be aware of, but I encourage you to take the reins and research everything possible on the subject.

Oscars are basically ravenous feeders, so feeding them should be a breeze—and it is! But be warned, just because your oscar ferociously consumes all that’s edible does not mean that you are feeding him properly. The key is moderation.

Oscars are always in competition mode. They compete against each other and anything else that eats, including their tankmates. Special attention should be paid as to how much and how often your oscar should be fed. Since we already discussed what to feed your oscar, let’s now move on to how to feed these fish.

Juveniles

Small oscars that measure between 1½ and 3 inches should be fed at least twice daily. Now let me interject a point right here: these guidelines are estimates, and you will need to experiment a little to see what works best for your situation.

Generally, small fish need to feed at least twice daily, and juvenile oscars are no exception. I tend to only feed baby oscars until their bellies are slightly distended; that is called feeding satiation. Try and vary the foods a bit, even on a daily basis. For example, mysis shrimp in the morning and a staple pellet in the afternoon or early evening. Also make sure that you are offering a small amount of food at a time. Let the fish actually swallow some before you dump more in their tank. If you add too much, oscars tend to gum and spit their food in an effort to move on to the next piece that is offered. Basically it should take longer than 10 seconds to feed your fish. You enjoy watching your oscar, so take your time!

Subadults

Most species grow very fast as juveniles, but few continue to grow as fast when they get to the sub-adult stages. Oscars are one of the few. Feeding oscars in this growth stage is very easy. By the time they hit 4 inches long they are well established. When they grow to between 4 and 6 inches continue to feed them daily, but perhaps alternate their feeding schedule; one day feed them twice and the next day just once. This will allow them to get daily nutrition, but it is curtailed just a bit. Remember, keep their diet varied for best color and vigor.

Adults

At about 7 or 8 inches we consider oscars adults. I have seen 5-inch specimens actually lay eggs and produce viable offspring, but I feel they (the adults) were stunted. At this time you should be feeding a very wide assortment of foods. Now is the time to really watch the weight of the oscar. If you feel that he is a bit too chunky, then play around with your feeding regimen. I have seen many hobbyists feed adult oscars only twice weekly; however, I feel that because of the gluttonous behavior of adults and the punishment that such beasts will unleash on their tankmates, the best regimen is to feed them every-other day, and twice weekly feed the adult two or even three times in a given day.

It is common for large adults, say over 12 inches, to feed on a very narrow scope of foods. This is most likely because they have never been offered them previously. If you raise a small oscar on a widely varied diet, then you will eventually have a very large oscar that will continue to feed on, quite literally, anything edible. And that’s the way it should be!

Amazing Pets

Oscars are true aquatic pets. They can recognize their owners and are accomplished beggars when it comes to feeding time. Offer them a varied diet and be careful to not overfeed, as they don’t usually need as much food as their dog-like behavior may lead you to believe. If you provide them with a large well-filtered aquarium, good quality food in moderate amounts, and lots of attention, then there’s a good chance your oscar will give you many years of fun and enjoyment.