Extreme Fishes

Not every fishkeeper is content with a 20 gallon tank with a school of neon tetras and zebra danios. For some folks, a fish is hardly a fish unless it’s a foot long and eats pellet food out of their hand. As large aquariums and their accessories have become more affordable and commonplace, the demand for large fishes of twelve or more inches has increased steadily.

To stock any number of good-sized aquarium fish, the dealer will need to provide a substantial number of good-sized tanks. A modest setup could include a 120 to 180 gallon aquarium to display some of the more attractive animals, and half a dozen or more 40 to 50 gallon tanks for the overstocks and incompatible species. Each tank should be at least 36 inches long and 18 inches from front to back, to allow room for a foot long fish to swim and turn around without difficulty.

Once the lunker section is ready, you’ll need to locate some fish to put in them. Your regional aquatic wholesaler or ornamental fish farm may do an excellent job of supplying swordtails, tetras, barbs and all the smaller, bread-and-butter species and even young fish of species that eventually get large. But in general it’s not practical for them to devote space, food and maintenance resources for the many months it might take to grow fish to a substantial size. In addition, shipping and handling fees can easily inflate the landed cost of large specimens to the point that they will be difficult to sell profitably. Air freight and packing charges totaling $20 add only a few cents to each of 400 zebra danios in a box, but mean that a $10 twelve-inch Oscar shipped all by itself really cost the dealer $30.

A much more cost-effective source for larger fish is one that you see in your shop every day: your clientele. Many hobbyists purchase small fish that quickly outgrow their aquariums, or tire of the amount of food and maintenance that a tank full of these brutes can entail. Rather than dump their pets in the local lagoon (a practice which is environmentally unsound and possibly unlawful) or otherwise dispose of them, they’d be happy to bring them to their favorite fish store in the hope of finding good homes. Properly handled, this can be a win/win situation, with the hobbyist finding an outlet for his outcasts, and the dealer finding an affordable source for large, quality fish.

There’s often a hidden benefit to accepting trade-ins on large or aggressive fish: the sale of a whole tankful of new fish. Many aquarium keepers end up with a tank devoted to a single specimen that has outgrown or vanquished its previous tankmates. Having a good home available to this solo act opens up the tank for new and exciting uses.

Negotiating a purchase price may take a little practice at first. It is very important for the dealer to consider all the after-purchase expenses he will encounter, and to leave a healthy profit margin to cover them. Large fish continue to eat and produce waste in abundance in the retailer’s fish room, just as they did for the home aquarist. In addition, there should be room to mark down for clearance, in case you suddenly find yourself with a dozen full grown oscars or plecostomus, or five tanks each holding a single murderous snakehead or red devil. Payment will probably be in the range of 20% to 50% of the intended selling price, preferably (from the dealer’s point of view) paid as store credit for other merchandise.

Payment price should reflect much more than just the gross weight of the animal; other factors such as condition, rarity, popularity and current stock levels also help determine value. An exceptional specimen of an unusual variety might be worth paying a bit extra for, as could an average specimen of a type that has sold quickly in the past. On the other hand, if you find yourself with an overabundance of a given variety, it’s a sign that it’s time to start paying somewhat less on that species. Most individuals will have a few fin tears and missing scales from being handled, and probably a few battle scars as well. These are quite unavoidable and shouldn’t affect the pricing very much. Deformed, damaged or unhealthy fish might be purchased at a greatly reduced price, but unless there is an unlimited number of aquariums available, they are best taken as donations or not accepted at all.

Once word gets out that your shop accepts trade-ins of larger aquarium fish, it can be quite a draw for both buyers and sellers. In fact, it is entirely possible that some of your competitors with more limited space or less interest in these species will actually refer customers to your shop. This is perhaps the ultimate in “advertising that you just can’t buy.”

New fish should optimally be quarantined, but that’s not always practical. At the very least, they should be closely monitored for compatibility and any signs of illness after handling. In an ideal setup, the receiving tanks should be near the checkout counter, or in some other highly visible place where employees will notice any major skirmishes.

Since there aren’t any wholesale guidelines to work with, setting a retail price can be a rather arbitrary process at first, to be modified as the seller gains more experience. Since the supply of most larger fish will be very limited, don’t be afraid to price a little higher if you believe there will be a demand. Prices can always be dropped on slow movers, but can never be raised on fish that are already out the door.

In addition to pricing, there are a few other issues that are particularly important when selling large fish. Compatibility is a major concern: assembling a collection of small, relatively peaceful tetras and barbs may be an art form, but creating a harmonious mix of these big brutes is more like playing a slot machine in Vegas. Most of these fish, and especially the cichlids, will be adult, territorial bad boys who basically don’t want any other fish that looks or acts the same to be in plain sight. Sometimes the newer fish are tough enough to hold their own immediately after be added to the established group, but more often they really take a beating. If the customer already has a few larger fish in his tank, he needs to be advised to watch closely for signs of injury, and be ready to remove fish if necessary. Unless a new fish is tough enough to hold its own or smart enough to take cover, it can be battered almost beyond recognition in twenty minutes, and killed within a few hours.

Chemistry is another concern; just because a fish is big and tough doesn’t mean that it’s invulnerable. Tanks stocked with larger fish frequently have problems with what I like to call “Old Tank Syndrome,” caused by inadequate water changes and evidenced by very high nitrate and crashing pH levels. As fish waste products build up over months or years, existing fish have a chance to slowly acclimate to the terrible water quality, but new fish may go into immediate shock upon be placed in such tanks. And if the chemistry doesn’t kill the new additions on its own, the older existing fish often attack the stressed and weakened newcomers with great enthusiasm.

Brand new tanks pose a similar threat. Again, fish that look and act tough are just as vulnerable to the high ammonia and nitrite levels of a tank going through its “break-in” cycle as most other fish. Newly set up tanks should still be broken in with other, hardier fish and/or large quantities of gravel and decorations from an existing tank. Ammonia and nitrite levels should be monitored until both have risen and then disappeared before adding any but the hardiest of fish.

The store’s replacement policies should reflect the higher risk of mixing big or aggressive fish, and customers should be forewarned of potential problems before making a purchase. This is no place for a 72-hour “no questions asked” guarantee, as many fish can be in fine shape when they leave the shop yet dead within a few hours in the wrong aquarium. Incompatible specimens that are returned within a few days in good condition should be accepted for store credit – for the fish’s sake as well as customer service. There’s no sure way to determine in advance which species – or even specimens – will get along, and what seems like an identical collection will work just fine one time and fail miserably the next. It’s the dealer’s job to help the customer make a wise choice (see side bar), but ultimately only the customer can watch new arrivals, and separate those that aren’t working before severe damage is done.

Stocking and selling large aquarium fish can be both fun and profitable. It wouldn’t be advisable to give up on the guppies and mollies just yet, but once in a while it pays to think big.

SIDE BAR: Mixing the Meanies

When you think about it, what we’re really trying to accomplish is somewhat of a contradiction in terms – a tank full of really mean fish that all get along together. While no one can guarantee success, here are a few tips that should improve the odds:

  1. Try to add all the fish before they are mature and developing their strong sense of territory.
  2. The more fish resemble one another in appearance or behavior, the less likely they will get along.
  3. New fish should be a little bigger or more aggressive than older fish; remember they already have at least two strikes against them after having been handled and moved to an unfamiliar setting.
  4. The tank should be as large as practical, with plenty of places for the new arrivals to become “out of sight, out of mind.”
  5. Rearrange decorations – which also serve as territory markers – immediately before adding the new fish. The squabbles of redistricting may keep the older fish occupied long enough for the new ones to settle in.
  6. Keep a very close watch the first few hours, and a close watch the first few days. If a new fish is constantly being harassed, it will need to be removed from the others.

SIDE BAR: The Cast of Characters

Here are a few of the more popular “big fish”, with some brief notes.

Oscars (Astronotus ocellatus) are the quintessential “big fish”, they’re actually much less aggressive than their reputation, and often take a beating from other large cichlids.

Red Devils (Cichlasoma labiatum) basically hate everybody, and declare about 100 gallons of space as their territory. They make great solo fish, but generally need huge tanks to have any chance at compatibility.

Snakeheads (Channa sp.) are very powerful predators that want to be alone, and require a huge tank to attempt to mix with others. They are sometimes blamed for actually breaking the glass of an aquarium.

Arowanas (Osteoglossum bicirrhosum) are very bizarre and attractive in appearance, but can get 3 feet long and are prone to flying out of the tank in panic. They are also relatively peaceful with fish near their size, and vulnerable to attck by more aggressive species.

Clown Knives (Notopterus chitala) are not terribly aggressive, and are again prone to being attacked by some of the more assertive species. They generally prefer live foods, and sometimes accept frozen.

Pacus (Myleus sp.) are the big cousin to the piranha family, and can get to 50 pounds or more. They eat mostly plant material in nature, but will happily accept nearly anything that fits in their mouths.

True Gouramis (Osphronemus goramy) are not very aggressive for their size, and eat most foods readily.

Redtail Catfish (Phractocephalus hemiolopterus) get too large for any tank less than 1000 gallons, and greedily gulp down any other fish that fit in their mouths. They are very prone to a deadly skin condition if kept in too small an aquarium.

Channel Catfish (Ictalurus punctatus) also get quite large and require very large quarters (like the Mississippi River). They tolerate crowding better than some other large catfish, but seem to compensate by attempting to skin other fish in the tank.

Shovelnose Cats (Sorubim and Pseudoplatystoma sp.) are generally quite hardy, and not very likely to be picked on. They range in size from about 18 inches for the common lima species to over three feet on the tigers, but all have huge mouths capable of gulping down fish over half their size.

Tinfoil Barbs (Barbodes schwanenfeldii) are often fast enough and unrelated enough to mix fairly well with more aggressive species. They eat prepared foods readily and are generally very hardy.

Iridescent Sharks (Pangasius sp.) can get up to three feet long, but are very vulnerable to attack by even some of the less aggressive species, often losing eyes or finnage. They are also quite active and require quite a bit of swimming room.

Silver Dollars (Metynnis and Myleus sp.) are also quite active and different enough that they tend to mix fairly well. There are a number of species, some of which do not get large enough for this application. The Red Hook is a particularly attractive species that gets over 12 inches long.

Lyretail Plecostomus (Hypsotomus plecostomus) – the common one sold as algae eating fish – can grow to be several feet in length. Their heavy armor makes them almost invulnerable to attack by all but the most aggressive species.

Saltwater Groupers are the equivalent of freshwater Oscars. They’re cute as babies, but grow quickly and often swallow their smaller tankmates.

S tankmates.

Saltwater Lionfish are of course venomous, and must be handled with great care – especially large specimens. They often prefer live or at least frozen foods, but are too slow to compete for them with more assertive fish.

Saltwater Sharks probably don’t belong in the home aquarium. Many varieties can get 6 feet or more in length, and the active species damage themselves by incessantly running into the corners of standard rectangular tanks.

This article originally appeared in

Pet Age Magazine