Top of the Food Chain: Aquarium Care of the Gulper Catfish Asterophysus batrachus

Author: Brian M. Scott

Natural History

The gulper cat Asterophysus batrachus Kner, 1858 is a member of the family Auchenipteridae (driftwood or auchenipterid catfishes), which occur in rivers from southern Central America to extreme southern South America (specifically Argentina). The auchenipterid cats all exhibit a scaleless (or “naked”) body and three pairs of barbels (except in one species), of which the maxillary pair is the longest. The pectoral and dorsal fins have a strong anterior spine, and an adipose fin may either be present or absent. They are chiefly found in fresh water, with the exception of one species, Pseudauchenipterus nodosus, which is known to enter brackish waters on occasion.

Native Range and Habitat

Asterophysus batrachus is a native of northern South America, specifically the Rio Orinoco and Rio Negro drainages of Venezuela and Brazil, respectively. Throughout its range, the gulper cat inhabits areas that are slow-flowing and abundant with submerged structure. Being somewhat bulky in build, they do not have the ability to withstand strong, rapid currents. However, they are sometimes seen in areas that have a stronger current than the waters in which they are typically found. Some hobbyists report their gulper cats doing quite well in large aquariums with a turnover rate of as much as 20 times the tank’s volume. Therefore, what is selected as prime conditions in nature and what we have the fish deal with in aquariums are indeed usually quite different. By providing some (not too much) driftwood or other decor to break up the current, it makes it very possible to keep this species successfully in a high-flow situation.

Space Requirements

At a total length (TL) of about 12 to 14 inches, the gulper cat is at home in moderately sized aquariums holding an average of about 100 gallons in volume. As with all species of fishes housed in captive conditions, it’s not necessarily the total volume that’s important, but rather the measurements in which that specific volume is laid out, which is more appropriately referred to as the container’s “footprint.”

The ideal 100-gallon aquarium for a fish the size of the gulper cat would have a footprint that measures 72 x 18 x 18 inches; while this aquarium footprint is sadly no longer a standard size offered by the major aquarium manufacturers, it may be had through special order.

Decoration and Substrate Selection

Due to the soft, sensitive (scaleless) skin of Asterophysus batrachus, it is typically advised to use a sparse approach to the tank’s overall decor. Being a type of woodcat, combined with the fact that they are found in areas where there is an abundance of submerged structure (usually in the form of wood), it is perfectly acceptable to use any of the various types of driftwood or bogwood available at your local pet shop. Of course, be sure that any wood that is to be used in the aquarium is cleaned appropriately prior to introduction to your aquatic collection.

Substrate, on the other hand, is less likely to be as much of an issue in regards to its ability to scratch the sensitive skin of your gulper cat(s) or other fishes. While in most texts it’s stressed that the substrate should be rounded pebbles and the like, the hobbyists that were sourced for this article indicated they paid little attention to substrate selection, and none had any issues to date. That said, it is still advised to be on the safe side and stay away from a substrate that is large and noticeably sharp or rigid. Basically, if your fingers are chafed after running them through it a few times then don’t use it with gulper cats, or any catfishes for that matter. The same would apply to other scaleless fishes such as loaches and eels.

Foods and Feeding

Feeder Fishes

Gulper cats are strict carnivores by nature, but that does not mean they do not benefit from the addition of some vegetable matter into their diet. Of course, the problem of getting them to voluntarily ingest this material arises. One way to combat this issue is by gutloading live feeder fishes, such as goldfish or minnows, with a high-quality diet of prepared foods, such as any of the vast assortment of flaked, pellet, or granular-type foods offered by aquarium shops.

Typically, the bellies of the feeder fishes should be rounded out using these foods and then immediately offered to the gulper cat and any other predatory fish that is being fed at the time. It’s very important to realize that most fish, especially minnows and goldfish, generally have very high metabolisms and tend to cycle through these foods very fast. So if you offer your feeder fishes such foods before leaving for work or school in the morning, then feed them to your gulper cat upon your return many hours later, you will not be maximizing the effectiveness of the gutloading technique.

Gutloaded Creatures

Generally, it is suggested that any gutloaded creature, whether it be fish, amphibian, insect, or worm should be offered to the predator within one hour after gutloading is completed. This timeframe will allow partial digestion of the plant material by the host animal, and thus the predator will have an easier time of extracting the needed nutrients from the meal.

Alternative Foods

Alternative foods are often recommended by highly successful keepers of these fish, basically whole seafood and other types of meaty diets. It’s important to never underestimate the use of a high-quality pellet or kibble type of food, either. Recently (within the last decade or so) the quality control and palatability of these foods has increased enough where we are finding them to be indispensable in the successful rearing and maintaining of many species of fishes, both freshwater and marine, in home aquariums.

Catfish in general show very positive results when a diet consisting mostly of catfish feed is used in their maintenance. As a result, several of the most popular fish food brands have come out with their own versions of “catfish chow,” and all are excellent. It’s highly recommended that several of these foods be purchased and combined together in an airtight container and used as the staple diet of this species, with offerings of seafood (clams, squid, chunked fish flesh, and shrimp). Gutloaded feeder fishes should also be used intermittently.

Tankmates

As a general rule of thumb, the use of tankmates in the gulper-cat aquarium is not recommended unless the prospective additions are significantly larger than the gulper cat itself. The problem arises with the fact that gulper cats can eat creatures half as large as themselves, and while they cannot eat creatures their own size or larger, they will often still try! This can lead to at least one dead fish, and sometimes two; it’s a situation that is unacceptable either way.

Tankmate Size

Which leads to the major question of what is safe to add. After all, few hobbyists are keen on single-specimen aquariums, and most prefer to have more fish mass then they really should have in the first place. A list of gulper-cat-safe tankmates will vary from hobbyist to hobbyist depending on their experience with this species. Generally speaking, it’s advised that any prospective tankmate be at least 3 to 4 inches larger than the gulper cat. This size difference must also be maintained throughout its life stages.

Avoid Aggressive Tankmates

Next, the tankmate should not be aggressive in the sense that it will pick at the fins and barbels of the catfish. This will annoy the gulper cat to no end and result in serious stress. Finally, tankmates should not be overly territorial types, so large cichlids and sunfishes would not be suitable. Gulper cats like to roam their aquariums, so having a territorial bully in there will only make the catfish’s life miserable. Of course, when you start dealing with aquariums that are extremely large, the rules can change, at least a little.

On the other hand, don’t forget that catfishes are generally nocturnal or crepuscular creatures, which may not sit well with prospective tankmates. Strictly diurnal fishes, such as arowanas for example, will often be jolted by the nighttime forays of the gulper cat. Fish behavior is a fascinating area of study, and it’s extremely important to know as much as possible about the behavior of your personal fishes so the best matches can be made.

Water Quality and Care

Most catfishes, gulper cats included, are not picky about the quality of their water. However, many other fishes are, and if the gulper cats are housed with other ornamental species then it will be in your best interest to maintain as healthy an aquarium as possible for them. That said, maintaining a healthy, well-balanced aquarium can be as easy or difficult as you want it to be. In most cases the feeding schedule and the type of foods offered will largely dictate just how stable the water chemistry will remain. When dealing with large and semi-large fishes that are predatory in their dietary requirements, chances are it will take a bit of work to maintain the system to acceptable levels.

Generally this is an easy feat, especially for veterans of the fishkeeping world. The answer almost wholly derives from a simple task called water changes. The changing of poor-quality water with some that is significantly better is usually enough by itself to maintain most systems sufficiently. Sometimes fishes are pickier about water chemistry parameters such as pH, hardness, or salinity.

Thankfully, gulper cats are not picky about such things, and clean, well-balanced fresh water is about all they need to stay healthy in aquariums. Of course, extremes in pH and hardness should be avoided. Keep the water as close to neutral as possible, and always keep a careful eye on nitrogen compounds (i.e., ammonia, nitrite, and nitrate). Any nitrogen compound should be kept as close to zero as possible at all times. Usually in systems that have many fishes in them, it will be close to impossible to maintain a zero reading of nitrate. This is fine, as long as levels do not exceed 200ppm, and a level closer to 50ppm is a better goal to strive for.

Water Changes

There are two words that come to mind regarding water changes for predatory fishes: frequent and massive. Water changes should be performed frequently and they should be on a large scale. As long as the water being replaced is of the same temperature and the same general hardness and pH of the existing water, then change as much as you feel safe changing. If the pH of the “old” water is, say, 5.5, and the pH of the replacement water is around 7.5, then you will probably shock the fish and perhaps even kill them. Use common sense when changing water. In the end, you are striving to replace poor water with water that has no traceable levels of nitrogen compounds or metabolites.

Conclusion

Gulper cats are fascinating semi-large catfish. They can be maintained in reasonably sized aquariums, and as long as proper caution is exercised they can be maintained with other fishes. A strict carnivore by nature, the gulper cat benefits from some plant matter included in its diet, usually introduced through gutloading feeder fishes. The quality of their water does not have to be perfect, but extremes need to be avoided. Large, frequent water changes are recommended and should be done as often as possible. Common sense is a hobbyist’s best friend when it comes to keeping these amazing catfish.

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