Stock - The Inhabitants
Fish Compatibility - A Complicated Issue
Written by Friday, 28 June 2002 02:00
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Being a member of the African Cichlid List I have a first hand view of the problems and issues that really interest fellow hobbyists, especially the ones keeping cichlids from the African Rift Lakes. I have repeatedly come across hobbyists complaining that one species bullied other species in their tanks or even killed them (which is also common in tanks housing their New World cousins). Moreover, many newcomers ask the question "which species are compatible with the one I like or keep". Since there has been some ongoing discussion on mixing cichlids and the fear of side effects usually following the wrong decisions (= dead fish), I would like to make some points which may help fellow hobbyists understand some of the key issues.
When selecting fish for your tank you should stop and think first. Otherwise you will have to run later, and, surely, you are going to regret that. For example, if you are planning an African cichlid tank it is better to house either mbuna or non-mbuna. These two types of fish do not mix well. After all, even in Lake Malawi, the latter feed on the former therefore you don't want this demonstrated in your tank, do you? But the Lake is millions of gallons of water with tons of rocks and infinite numbers of hiding places, your tank isn't. Therefore some things that would happen in the Lake will never take place in your tank, while other things, never happening there, will take place in the limited space of any tank. In the end, it is not just keeping them alive. It is more like choosing which species will live happily thereafter! To make sure all of yours will, you need to be stocking your tank with compatible fish.
What is the term compatible fish refer to ??
Normally, we use this term to speak about fish that need the same water chemistry (pH, GH, KH) and physicochemical characteristics (temperature, conductivity, osmolarity etc.). I am sure you know the rule of thumb : "do not mix American with African cichlids because of their different water requirements". So most people know that Discus thrive at a pH lower than 6.8, almost distilled water and frequent water changes, American cichlids usually prefer a neutral or slightly alkaline water (pH 7-7.5) and are not very particular on the salt content of their water and, finally, cichlids from the African Rift Lakes (Malawi, Tanganyika and Victoria) require alkaline water (pH 7.8 - 9.0; depending on the Lake) and a mixture of salts in it. Most newcomers don't even go that far; shape and color are the primary (if not only) concern. And then, problems start. Fish get bullied, constantly chased, hide behind the filters, refrain from eating, get sick or just get killed by their tankmates. Although a fight resulting in a wounded or even killed fish in a tank is something that can't be completely avoided, losing a fish every day is unnatural and is - almost exclusively - a sign of incompatibility.
Temperature. The lower the temperature (25 degrees C) the less the aggression, the less the appetite and the longer your fish will live. As we move to the upper limits (28 degrees) you get more of aggression and appetite but less life span. A note for you : the average carrying time for any mouth brooder female is calculated assuming an average temperature of 26 degrees. If your tank has a lower temperature than carrying will take longer (4 weeks instead of 3). If your tank is at 28 degrees, then your female may release the fry on the 16th day (it happens to me regularly, during the hot Greek summer months - the water temperature may reach 30 degrees).
If water parameters was all there is to it, then "compatibility" would be a very easy issue to be addressed and everybody would be able to cope with it. Unfortunately, "Compatibility", as a term, is a much broader parameter and covers many more issues than just water chemistry. It is because of this reason that most hobbyists run into troubles after a short while. I will just list (and shortly explain) a few parameters that I have personally known to play a key role in the well being of our aquatic pets. I will even go as far as give some examples from my own experience with the African cichlids of Lake Malawi which definitely allow very little space for wrong decisions as far as tankmates are concerned.
Dietary needs. Species are classified as being omnivores, piscivores, herbivores, carnivores, insectivores etc. For instance, Mbuna are herbivores, non mbuna are insectivores, carnivores or piscivores. This has to do with their primary feeding source and should always be taken into account. Of course, in nature, fish will feed on what is available or easier to get but they are usually specialized on chasing, grabbing, grazing, eating and metabolizing a specific kind of food - on which they usually feed. Feeding the wrong food in our tanks can lead to all sort of problems, among them the - usually fatal - Malawi bloat (which doesn't affect Malawi cichlids only). If the tank is not stocked properly, correctly feeding some of the fish will harm the rest and vise versa. The intestine of all species is suited to the food they should take and can't "use" other type of foods efficiently. This has to do with the length and special construction of the intestine walls and can't be adapted to the wrong food. Herbivores for example, are accustomed to the high cellulose content of algae and can fully utilize it with their special mouths, teeth, stomach and longer intestines. A piscivore, fed on the same diet will manage to get only a fraction of the nutrients from it, and in most cases, basic elements needed for its growth will not be present in adequate quantities. In short, all species can take the wrong kind of food every now and then but they shouldn't be fed constantly on the wrong type of it.
On top of that, fish eating at the surface of the water prefer food in flakes, bottom feeders prefer sinking pellets or tablets, midwater feeders prefer slowly sinking pellets etc.
Another point to consider is the size of the fish you are planning to keep in the same tank. A small female Nimbochromis venustus will be chased by all males in the tank as well as all the grown up females whose color, shape and pattern resemble hers. In short, if not dead within a week, a really unhappy fish - and shortly, a sick fish. Needless to say, never add a male which is considerably smaller than an already existing male. Better still - never add a second male. For species which are really aggressive (Melanochromis sp., most Pseudotropheus sp., Nimbochromis venustus etc.) a second male will trigger uncontrollable fights and deaths. Even males of the most peaceful species will chase rival males all day long if not just kill them.
Fish size is also important when it comes to feeding. It is evident that you can't feed your foot - long Astronotus ocellatus (commonly known as Oscar) with baby growth food or your Barbus sp. (e.g. tiger barbs) with big size cichlid pellets. If you feed one type of food, some fish will be underfed while others will be overfed.
Assuming you have a tank filled with fish which are incompatible as far as their dietary needs are concerned, you may have to use two or more sizes from every food they need. Surely, it would be easier if this kind of compatibility was checked when you were selecting them, isn't it? A classic example of keeping (dietary) incompatible species together is the common African Cichlid tank where usually mbuna (herbivores) are kept with Malawi Haps (a very common species: Sciaenochromis fryeri), or even piscivores (Nimbochromis venustus is very often seen in such tanks).
Fish temperament Some species are listed as "aggressive" in the literature and this is a warning that every hobbyist should take into account when selecting fish for his / her tank. Aggressive means that the fish will usually form a territory (mostly the males) and will defend it against all intruders. The male will chase, nip, wound or kill any fish that doesn't seem to get this message. This behaviour doesn't mean that the fish is "bad" since it is part of its natural behaviour (usually fierce competition for food or territories in their natural habitat). Keeping such species in small tanks is the perfect way to create a battlefield until the problem is solved by the fish itself (by killing most fish in the tank). Naturally a 25 cm spawning male Nimbochromis venustus will not tolerate any other fish near its spawning site. If the nearby fish is of the same size and behaviour the spawning male will react in a much better way (milder). If it is a 7 cm fish (no matter what species) its reaction will not be the same. If there is a lot of spawning going on in your tank then any small, mild species will have a really bad time.
Tankmates should be selected among species of the same size and temperament, while ample space and hiding places are a must. In such an environment, full of compatible fish, a dynamic equilibrium will soon be reached and the tank will go on for years without any serious problem. If I were to give some examples of aggressive species I would name the Melanochromis genus (most notably Melanochromis auratus and chipokae) and some American cichlids (Astronotus ocellatus, Cichlasoma nicaraguensis etc). These are species known to be really aggressive. However, as you can see elsewhere in this site, I have kept 5 Melanochromis chipokae males, 13 Melanochromis chipokae females, a colony of 10 Melanochromis auratus (1 male and 9 females) along with a Pseudotropheus lombardoi pair in the same tank for three years without any serious problems. Fierce fights were observed every now and then but after a while everything was peaceful again.
It should be noted that the listing of a particular species as "peaceful for an African" is only a general remark which describes the average behavior of this particular fish. Individuals can greatly vary (as with all animal species). I personally own a male Cyrtocara moorii which is the hyperdominant fish in my non-mbuna tank (till now) and has shown to be very aggressive at times. If you check your books you will see that this was supposed to be a relatively peaceful species - well, mine is not.
Sex - related Compatibility This kind of incompatibilities has to do with the sex of the fish or the spawning / breeding habits of a particular species which may cause troubles to the rest of the inhabitants. Since fish is going to grow eventually, spawning is expected to take place if a pair is formed. If two or more males are present in the same tank, this also means problems. If only one female is present for a polygamous species, this will lead to problems, too. The aquarist should have already foreseen that and selected his fish accordingly.
Polygamous fish should be kept with more than one female otherwise the single female may be harassed to death by the male. Keeping more than one female will split the male's courting and aggression. A good example of this is most mbuna (rock fish) from Lake Malawi. Most of these species (Pseudotropheus, Labidochromis and Melanochromis being the most common genera) need a harem and will chase a female till it is exhausted or even killed. Usually a ratio of one male with 3-4 females will solve this problem.
Fish intolerant of its own kind and sex. Among cichlids this is the rule rather than the exception. Most cichlids will not tolerate the presence of a second male in the same tank and will do everything to correct the hobbyist's ignorance, usually by killing the rival male. In fact, a male may also chase any male whose color (mainly) or shape / melanin pattern resembles his. In some species, this kind of intolerance is also evident between females. A classic example is members of the Melanochromis genus. Melanochromis auratus and chipokae males and females are amongst the most intolerant species. I would like to note that in my tank, the dominant Melanochromis auratus male killed the second male within two weeks and kept on killing all male juveniles. As a result, after more than 25 broods, not a single male survived until I removed the adult male. With piscivores and large Malawi Haps, it is not possible to keep a second male, no matter the size of the tank. The same is true for most large American cichlids.
Easily cross breeding species. If something can go wrong it will. However, the fish keeper should be aware of that and not let it happen. What am I talking about? Hybridization. Some species are very prone to it, among them species of the genus Aulonocara (Lake Malawi, common name African Peacocks). The females of most species are almost identical and this will inevitably lead to hybridization. It is recommended that one should keep only one species in every tank, unless there is an obvious difference between both the males and the females. On the main, bear in mind that keeping species that have the same color combination is a sure bet to end up with fry you can't possibly tell which was the father! A good example is Aulonocara species. Though males may differ significantly, females usually don't. It doesn't take a genius to see the future. Choose fish that have different colors, if possible different shapes and / or different patterns. My male Nimbochromis livinstonii will not even take a second look at the female Nimbochromis venustus. The differences in shape and pattern are enough even though the colors (of the females) are pretty close. One of my "mistakes" is the Chilotilapia euchilus combined with the Protomelas taeniolatus. Though males differ a lot the females look very similar. I couldn't resist it! I just hope the females will look at the courting male before giving in! A very special note on this one: never sell or give away fry if you have the slightest suspicion that it may be a hybrid. These hybrids are fertile for a couple of generations - at least. You are not helping nature - you are destroying it. Either keep them yourself or dispose of them.
Spawning fish. The hobbyist should be informed how his fish will act when spawning. Even relatively peaceful or small species are transformed to aggressive menaces when spawning or guarding their fry. It is well known that cichlids are probably the best parents and they care for their broods and fry. Very often a pair of cichlids may kill other fish, which are regarded as intruders or a threat to their fry. It should be noted that when spawning, some fishes "enlarge" their territory considerably. If the tank is not big enough, this may well mean that there is no space for the rest of your fish. A good example is the African river fish Hemichromis bimaculatus (known as the Jewel cichlid). When this fish is spawning all other fish in the tank become endangered species. It goes without saying that, the bigger the fish, the bigger the problem will be.
Spawning aggression. Hemichromis bimaculatus (photo above), widely known as the Jewel cichlid, is a truly magnificent fish. However, when spawning in the limited space of an aquarium it becomes as deadly as it can get. Even the female may be killed on the spot if "she" doesn't accept the males courting. Certainly, getting six of them in a community tank will always result in big troubles. This species is simply incompatible because if its spawning behavior.
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