Fish Compatibility - A Complicated Issue - Page 2

Fish Compatibility - A Complicated Issue - Page 2

Written by George J. Reclos Friday, 28 June 2002 02:00

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Established fish hierarchy. This is one of the most forgotten aspects of "incompatibility". In any given tank, all inhabitants form a hierarchy which is only changed when a fish gives a successful fight and gets a higher place in the tank. This hierarchy is in a dynamic equilibrium and will change all the time with fights or when a fish is sick or weaker. The rest of the fish will immediately rearrange the order and everything will go on smoothly while the sick fish will be chased, bullied and finally drop many places in the hierarchy, losing its territorial rights as well. If a fish - for any reason - is removed from the tank and subsequently returned in the tank, it will have to fight its way back to its original place in the hierarchy. Every hobbyist can see that in his own tank if he or she spends some time in front of it. When a hobbyist adds a new fish in an existing cichlid tank, it should be larger and a bit more aggressive than the fish already inhabiting the tank. Many fights and kills are due to this reason. This usually puzzles the hobbyist since he can't understand why his fish was killed when re-introduced in the tank while it was never chased before. A way to solve this problem is to start with larger peaceful species first, let them acclimatize and then add the more aggressive fish which should be a bit smaller in size. This will guarantee that the milder species will have some time to get the best hiding places and territories.

Fish size is a very important factor. Most people realize that, so there is no need to go into many details on this one. A two feet American cichlid housed with any small fish is going to be very lonely in a short while. Even fish which are usually herbivores will not refuse a free meal if offered by the hobbyist - even mbuna will eat fry if they find it. Size is also important in many other aspects of life in the aquarium since whatever the large fish does (spawning, taking care of its fry) may have a direct and severe impact on the small inhabitants. It is always recommended that all fish in the tank should be size compatible to avoid problems. It should be noted that when you select fish for your tank, the important factor is the size of the adult fish and not the size of the fish you actually buy. Four inch could be the adult size of one fish (most mbuna) while it is only the size of a young juvenile for other species (Buccochromis sp., Astronotus ocellatus, large American cichlids). Therefore having a tank with various species, all sized four inches is definitely not a guarantee for a peaceful tank.

      

You Shouldn't mix a Predator with its natural Prey. This is the part most fish hobbyists don't take into account when selecting their fish and it is the most common mistake made by African cichlids fans. Mixing American predator cichlids with African predator cichlids in a tank with average water parameters can, perhaps, makes more sense than mixing the predator and its natural prey in the same tank. Why? For many reasons, but I will just give the three most important ones.

Firstly, both the predator and the prey will have optimal water conditions which means that everyone will play the role it should in a perfectly balanced and protected environment. In the environment of a tank, the predator doesn't have any natural enemies (in contrast it has you, the hobbyist, taking care of its good health) while the prey can't use its only option : escape. In short, the predator finds itself in a paradise. Many small fish to eat, with nowhere to go and in very big numbers.

Secondly, in such a case the predator (coming from the same Lake as the prey) will immediately recognize the melanin pattern of the prey (it is genetically built to do that). In short, when the disaster takes place ( "my Nimbo seems to have eaten my poor Aulonocara") it means that someone didn't do his homework - while definitely the Nimbochromis did its part. I use the Nimbochromis genus as an example because this genus includes dedicated piscivores that will sooner or later behave naturally if given the chance (Nimbochromis venustus, N. livingstoni and N. polystigma being the most common in the hobby). I can ensure you that members of the Buccochromis genus are much more effective in this aspect but are not that common.

Thirdly, and perhaps most important is the evolution and the survival of the fittest things. According to this, these predators exist today only because their tactics have been refined and proven in the course of evolution which took them millions of years. They know exactly how the mbuna or any fry will behave and they will do what it takes, in a perfect, natural way. The mbuna lack the huge rocks which provide shelter and the predator won't go away after a first unsuccessful attack. It will stay nearby and will try it again and again until it succeeds.

It is worth noting that fish employing strange and unusual (for an African cichlid) ways of defense are able to escape. Akanthopsis choirorynchus for example, will burry in the sand when a predator closes in. Although the cichlid could start digging and corner the fish, it prefers to look for another, easier and familiar prey.

Most hobbyists try to recreate part of the Lake in their tank and want to include specimens from both worlds (namely mbuna and piscivores). What they forget is that these two worlds are interconnected and the second feeds on the first one.

           

Predators and prey. Definitely not the best combination for an African cichlid tank. Left, top: Buccochromis nototaenia; one of the most efficient predators even in a tank, will eat any fry it can catch while almost every mbuna - even adults - can be regarded as dinner. Its speed and maneuverability will almost always guarantee a successful hit. It will eat anything that can fit in its mouth. Left, bottom: Nimbochromis polystigma: Less efficient in a tank (usually chases by ambush) but equally deadly. Right, top: Cynotilapia mbamba juvenile 4 months old. Left, bottom: Melanochromis auratus 4 months old. These mbuna do not stand a chance if encountered by the predators in open water. Only the provision of many hiding places by the hobbyist will give them a chance to survive. The problem is that sometime they will get out of their shelter to eat. No matter when that happens, they will never be regarded as companions by the predators. I have personally witnessed the male Nimbochromis polystigma shown in this picture eating an 8 month old mbuna, measuring 6 cm. This was the time I decided to build a big tank to house the non-mbunas. In contrast, Akanthopsis choirorrhynchus (commonly known as the Horseface loach, see photo below) gets out of the sand every now and then to feed. When a cichlid tries to get it, the loach will burry in the sand with an amazing speed. The predators, unfamiliar with this kind of defense, after the first couple of failures will not even bother to chase it.