Evolution is a fascinating thing; whether through survival pressure or simple chance, sometimes we end up with some weird creatures on this planet.
Labyrinth fish are one example of this.
While they look like any other tropical fish, their bodies hide an unusual feature – an extra respiratory organ that enables them to breathe air from the surface.
History and General Information
Labyrinth fish – so named for their special labyrinth organ – include approximately 137 different species. All come from either Africa or Asia and many are well-known by aquarium lovers. These fish can range from as small as one inch up to 24 inches, depending on the species. The most popular pet varieties are Gouramis, Bettas (Siamese Fighting Fish), and Paradise Fish. Several other, larger species are also farmed for food in Asia.
Scientists believe that these fish are relative newcomers to the evolutionary timetable, and their labyrinth organ is evidence of that. Whereas more ancient fishes must rely solely on their gills for survival, Labyrinth fish can take oxygen from both the water and the air, allowing them to survive in more difficult environments and extreme situations.
The Labyrinth Organ
You may be wondering by now what exactly this organ is and how it works.
The labyrinth organ is located in a chamber above the gills in the fish’s head. It’s comprised of many small, maze-like compartments of thin, boney plates.
These plates, known as lamellae, are covered with extremely thin membranes of folded tissue liberally lined with blood vessels. This set-up allows oxygen to pass through and be absorbed by the blood vessels, which then transmit the oxygen throughout the body.
Interestingly, Labyrinth fish are not born with fully-functioning labyrinth organs. It develops as the fish matures. However, while this unique organ makes it possible for these fish to breathe in two different ways, it also makes it necessary.
Most adult Labyrinth fish must derive some of their oxygen from the atmosphere because their gills are not sufficiently developed to provide adequate oxygenation on their own. This begs the question of how the juvenile fish survived while their organ was developing. Some suggest that the gills partially degenerate as the labyrinth organ develops.
Additionally, the size of the organ varies considerably, depending on the fish and its environment. As you might expect, species that inhabit ultra-low oxygen waters have much larger labyrinth organs than those who live in fast-moving streams.
The vast majority of these fish are native to southern and southeastern Asia. They inhabit the warm, acidic waters of rivers and lakes. A few species can be found in the southern half of the African continent in similar tropical waters.
Most Labyrinth species thrive in still or barely-moving waters with low oxygen levels, but a few do live in fast-moving mountain streams, as well. Their habitats are usually filled with thick plant life.
Because so many diverse species comprise this order of fish, it’s a bit hard to define aquarium parameters that fit all species’ needs.
In general, though, Labyrinth fish are a hardy group. They require warm waters that more or less mimic their native environments but do not demand narrowly-defined acidity, hardness, or other water parameters, as other species of fish do. A broadly acceptable range of water parameters would be temperature between 68-82oF, pH between 6-7.5m, and water hardness of 4-15 dH.
Because of their labyrinth organ, they’re not dependent on tank aeration, either. What they do require is sufficient surface area to rise to the top and gulp air occasionally. Most would also prefer not to have much of a current in their tank, either.
Another nice thing to have in your tank is decoration. Most Labyrinth fish would appreciate a few plants (live or artificial), some rocks, and even a piece of driftwood or two to play and hide in. It’s best to avoid overly-bright lighting, as well, since these fish are generally accustomed to smaller amounts of light filtering in through the plants and muck of their native habitats.
Lastly, they’re good jumpers and may launch themselves out of your tank if given the chance. You should have a tight-fitting cover for your aquarium.
Whether or not the Labyrinth fish you have your eye on would make a good community tank member depends greatly on which species it is. Many are perfectly calm and play well with others.
Some – notably the pugnacious Bettas – need to be kept in solitary tanks or they will fight to the death.
In some cases, males of the same species can get aggressive with each other, particularly during mating season. Your best bet is to do your research and consult the person or store you’re planning to buy from as to how many of a particular species you should buy and of what sex.
Good general tank mates to consider are Gobies, catfish, tetras, and the more docile species of Barbs.
Labyrinth fish are pretty laid back in this regard, as well. Some are carnivores who like to eat small aquatic organisms and carrion. Others are omnivores who will happily consume algae and small plants along with meat.
Most species will easily accept flakes and pellets, as well as the occasional serving of brine shrimp, worms, or other live or frozen food on occasion. As with most fish, varying their diet once in a while ensures that they get sufficient nutrients and stay as healthy as possible.
Breeding the Species
As if possessing a special secondary breathing organ wasn’t cool enough, the way that some Labyrinth fish breed is also fascinating.
Given the large number of species, there’s naturally considerable variation in breeding and brood care methods.
Some, such as the Kissing Gourami (Helostoma temminkii), are typical hands-off parents. They spawn and then go about their business, leaving the eggs and fry to fend for themselves.
Others, such as the Dwarf gourami (Colisa lalia), make bubble nests. They do this by blowing bubbles that stick together either at the bottom of the tank or the surface of the water (depending on the species). The male builds his bubble nest first and then courts the female. Once they have spawned, the male then guards the nest until the eggs have hatched and the fry become free-swimming.
Lastly, you have the mouthbrooders, such as the Betta pugnax. The male of this species catches the eggs after they have been fertilized and holds them in his mouth. After about four days, they hatch inside his mouth. The fry become free-swimming after another four days, and the male releases them and provides no further care.
In general, you want to provide a dedicated space for your Labyrinth fish to breed, regardless of how they spawn. You can do this by placing a divider in your regular tank, but, ideally, you should have a separate breeding tank that you can transfer mating pairs or groups to.
A dedicated breeding tank provides several advantages.
For one, you can control the environment to stimulate the spawning process. This usually involves lowering the water temperature slightly and adjusting other parameters as needed for the specific variety of fish you are breeding. You can also decorate this tank with extra plants, special substrate, or different hiding places, as needed.
Another advantage is that the breeding fish can do their thing uninterrupted and without the stress of needing to protect their territory from “invaders.” Plus, you’re able to continually monitor their progress and take appropriate action, as needed. For example, you usually need to remove the adult fish at specific points in the breeding process to ensure the safety of the eggs and fry.
Lastly, having a separate breeding tank allows you an uninterrupted view of the magic of this order of fish and their unique breeding mechanisms.