Scavenger Fish
The catfish are easily identified by the whiskerlike barbels that extend from their "noses," "lips," and "chins." Another peculiarity is that the true cats have no scales, though they sometimes possess a type of "shingle" that covers them. This "shingle" is very unlike the scales of ordinary fish and on some catfish looks much like the coats of armor worn by medieval knights; thus the name "armored catfish."
Most aquarists consider the cats as merely scavengers. The catfish are always busy poking their "snouts" into the gravel looking for any type of food. Dead leaves, food that has reached the bottom, dead snails, dead and decaying daphnia are all of interest to catfish, and they will devour them without much ado. The cats are very peaceful, seldom attacking any live fish, regardless of size—there have been only a few substantiated reports about individual cats eating small living fish. They will usually leave fish eggs alone, too, but when you spawn such fish as the zebra danio, which drops eggs onto the bottom of the tank, it would be more advisable to leave cats out of the tank.
The author has observed cats that were so bashful they would hide at the slightest provocation, yet when a school of daphnia was introduced into the tank, they would make one of their rare appearances and swim out and help themselves. This, however, is a rare example and not typical of the general behavior of catfish. After training, however, catfish even take floating food, turning upside down if necessary.
Certain fish are peculiarly adapted to do the work of a scavenger. The habits of the Corydoras, namely their preference for feeding off the bottom, make them ideal for this purpose. But other fish have the same property that also should make them desirable for cleaning purposes. The common guppy picks continually on any palatable matter that may be on the bottom of the tank and is often used for scavenging purposes. The name "scavenger," when used in connection with a certain class of fish, is much like the term "weed" when talking about a garden. Is a stray orchid a weed in a patch of dandelions? Yes, if you are primarily interested in raising dandelions! But there is bound to be trouble if the general name "scavenger" is used too freely.
The many fish that have tremendous appetites all might well be called "scavengers," but there must be a distinction: A scavenger is a fish that eats food that is left uneaten by the other fish in the tank. (Such animals as snails, clams, mussels, and shrimp may be included in this category.)
Scavengers eat not only food that the others have left behind, but there are those that get into places where the other ones cannot squeeze and pick up whatever is left there. This group includes the kuhli loaches, which include Acanthophthalmus kuhli, A. semicinctus, A. shelfordi, and A. myersi among others. These loaches have about the same body shape, elongated and snakelike, which lets them crowd into some very tight corners and get bits of food which would otherwise contribute toward fouling the tank.
Another type of "scavenger" has come to be known extensively as the Chinese algae-eater, Gyrinocheilus avmonieri. Whoever gave them the "Chinese" part of their name must have had an active imagination, because they come from Thailand, quite a stretch away from China. These fish have a very greedy appetite for algae and spend a great deal of their time foraging for it. They go over the glass sides of the tank, the rocks, plants, and gravel, and keep plucking at all the algal growths that come their way.
G. aymonieri is not alone in being a fish that will eat great amounts of algae. There are Otocinclus and Hypostomus species, all from tropical South America, that graze happily on algal growths and bits of uneaten food. As far as looks go, they are just about the unloveliest fish in existence. With many of them this is the secret of their charm. They rarely spawn in captivity.
At one time it was believed to be necessary for every well-set-up aquarium to have a few snails, but this is not so. Snails have their "pros" and "cons," which we list
here:
1. A snail consumes oxygen just like fish. For every snail you must figure one less fish of similar dimensions.
2. Snails greedily consume great amounts of algae, it is true. They often raise havoc with your valued plants as well.
3. A snail will dutifully clean up uneaten food but will also leave behind it a number of messy droppings.
4. Snails are very prolific, and disposing of the young often becomes a problem.
So there you have it. They have their good points, but in order to benefit by their good points, you have to put up with their faults.
It is well known that daphnia feed readily on most types of infusoria and green algae, and it is standard practice to introduce daphnia into a tank that is cloudy or green. In doing this, one caution, however: Remove the fish. Not only could the fish overeat and thus reduce the number of scavengers, but the tank might not be able to support so much life at one time. The water could become too saturated with carbon dioxide and thus poison all the inhabitants, or the fish might turn on one another and kill themselves, which often happens in densely populated aquaria.
Sometimes freshwater clams or mussels are placed in the tank to help keep the water clear. These animals serve their purpose well as they obtain food by sucking water through a set of filters and thus remove most types of suspensions, whether digestible or not. Although these animals have unusual capacities for clearing water, they do represent a hazard. Should one die it might go unnoticed for a few days, since they are not very visibly active, and their decaying would do more damage than they could ever do good. Also, several large fish may peck at them, causing them untold grief; or, as the author has witnessed, large fish (Ast•onotus ocellatus) may try to ingest them—bettas also make their lives miserable.
Snails are undoubtedly the favorite as far as shelled scavengers go. They reproduce without any help, often producing a type of very nutritious egg that is enjoyed by many fish. Some snails produce live young (Japanese livebearer). It might be worthwhile to discuss individually each of the popular types of snails and their advantages, since they are so valuable when put to the proper task.
