Hobbyists that keep marine aquariums
have a great number of fishes to choose from when it comes times to
stock a tank, with many, many dozens, if not hundreds of species
available. The vast majority of such fishes added to folks aquariums
will be picked due primarily to their good looks, and possibly due to
some type of interesting behavior they exhibit. However, there are
numerous fishes that should be given a spot on an aquarists stocking
list for the jobs they can perform in a tank.
The Fish Cleaning Fishes:
Sometimes, even the fishes in an aquarium can benefit from a good cleaning, which can be taken care of by a number of relatively small fishes that specialize in cleaning other fishes. There are numerous types of such cleaners that will nip and pick tiny parasites, dead skin, scales, mucus, and such off other fishes, getting themselves a meal in the process. Of course, the fish being cleaned also benefits from this, as they get a good going over that they cant do for themselves.
The cleaning species are recognized by other types of fishes for what they are. So, fishes that wish to be picked clean will allow a cleaner fish to browse over their bodies, and will typically let them stick their head, or even swim, right up inside their mouths and inside their gill openings in order to do a thorough job. The cleaner doesnt have to worry about being eaten (except in rare cases), and will gladly go right to work inside and out. Note that fish parasites are particularly common and problematic on their gills, rather than on the outside of their bodies, so cleaner fishes may spend quite a bit of time working over the gills, more so than the body.
These cleanings obviously have their benefits, and eager fishes will often gather and line up around a known "cleaning station", waiting for their turn where one or more cleaner fishes hangs out. This relationship between cleaners and cleanees persists in aquariums, too, so adding a cleaner can help keep all the fishes in a tank in their best health. However, its likely that the most common cleaner fishes you'll see for sale are the cleaner wrasses (Labroides spp., usually dimidiatus), which happen to be the worst choices for your aquarium.
These wrasses are great at cleaning, but it is very unusual for them to learn to eat any sorts of fish foods that you might provide. They simple dont like fish food, as best as I can tell. This definitely a problem because in the wild (or in very large public aquariums and such) they have lots of big fishes to go over in any given day and can find plenty of food, but in a typical home aquarium there won't be enough cleanees to provide a cleaner wrasse with a steady supply of grub. So, they typically wither away slowly and eventually die of starvation no matter how much food you might give the other fishes in your aquarium. And on top of that, the removal of these fishes from their natural environment has been noted to affect the health of the cleaner-less fishes left behind.
Still, you shouldnt give up though, as neon gobies (Gobiosoma oceanops), sharknose gobies (G. evelynae), and yellow-line gobies (Elacatinus figaro) are good cleaners, too. They aren't as big or active as the wrasses, and don't have the colors that many wrasses have either, but they'll eat fish foods. In fact, they'll eat a lot of different foods, and can even be kept in aquariums with no other fish to clean at all. So, you dont have to worry about them starving to death, which makes them a much better choice than a wrasse. And, to ease your mind, aquacultured cleaner gobies are available, which means theres no negative effect on the reefs if you bring one of these captive bred specimens home.
Even though this article is about
fishes, I guess I should also throw in the fact that there is a variety
of shrimps that can make great cleaners, as well. So, if a cleaner goby
isn't what you're really looking for, keep an eye out for a
good shrimp and please leave the wrasses alone!
There are several substrate-sifting species available, with the yellowhead sleeper goby (Valenciennea strigata), the sixspot sleeper goby (V. sexguttata), and the dragon goby (Amblygobius phalaena) being three examples. Like other sifters, these will move around the bottom of a tank and scoop up mouthfuls of sand/fine gravel looking for tiny bits of food. This provides them with meals and also helps to keep the substrate clean in the process. They churn the bits around in their mouths, after which they drop from the fishes' gill openings, minus anything the fish considers edible.
Their activity keeps the substrate stirred up well, breaks up detritus, and also keeps algal growth down. This keeps the substrate cleaner looking, and also puts detrital particles into suspension where they can be collected by mechanical filters if you use them. There may also be an added benefit to any filter-feeding organisms present in the tank, which can make use of the fine detrital particles and various tiny organisms that may be freed from substrate by the fishes' activities.
Fortunately, these fishes will typically (but not always) learn to eat other fish foods that are offered, and thus won't starve if they can't get what they need from your bottom cover. However, you do need to keep in mind that these fishes can't handle medium to large gravel sizes. Thus, they should only be kept in tanks with appropriate substrates if you want to see them do what they do naturally and expect any work out of them. Also note that while they stay relatively small and some may do fine in mated pairs, most of them tend to not get along with other bottom-dwelling fishes.
The Algae Cleaning Fishes:
The first type of algae-eating fish
that typically comes to mind is a tang (also called a surgeonfish,
depending on who you ask). There are many types of tangs, and theyre
available essentially everywhere you look for good reason. Most all of
them are colorful and attractive fishes with some personality, and
theyre good algae-eaters, too. Various tangs will spend their entire
day roaming around non-stop, pecking and nipping at fine algae that can
form a coating on rocks and such, and larger macroalgae that sprouts up
and into the water, as well. In general, theyre all invertebrate safe,
as well, and wont bother your other critters. There are exceptions, but
theyre few and far between.
While they arent as popular in the hobby, the Rabbitfishes (some of which are called Foxfaces) are certainly good at removing unwanted algae, too. These fishes are typically very hardy and will also pick and nibble away at all sorts of algae. And like the tangs, these will generally leave your critters alone unless they are underfed. Ive found that they arent as picky about what they eat as some tangs can be, but again, there can be some size/compatibility issues with various species. Thus, youll need to do some checking before bringing one of these home, too. You also need to be careful with them if you ever need to handle one for some reason, as these are some of the few sorts of fishes that possess venomous spines. Fortunately, theyre not aggressive though, and wont come after you with their spines. Theyre for defense.
Next, there are the angelfishes. Larger angelfish species are typically unsuitable for life in reef aquariums, as their diets often include sponges, corals, and other invertebrates - and they can get really big, too. However, the smaller angelfish species (typically called pygmy or dwarf angels) are much more likely to stay out of trouble and do some work in the tank, too. Most of these belong to the genus Centropyge, come in lots of gorgeous colors and patterns, and also stay under 6 inches.
However, pygmy angelfishes arent as
desirable as the other fishes covered, because they typically just dont
go after algae they way tangs and Rabbitfishes do. But, they will
typically help out at least a little. Still, as is often the case,
there are some compatibility problems with them at times, as they often
dont get along with various other fishes. And, while they usually are
completely invertebrate-safe, there are individuals that may decide to
pester or nibble at various invertebrates like giant clams and some