Black Ghost Knifefish (Apteronotus albifrons) in a community tank? / Fish as gifts?
I recently got a fish as a gift from friend which I now identified as Apteronotus albifrons, Black Ghost Knifefish. Having read the descriptions in the book I now am somewhat uncertain whether I can continue to keep this fish in my community tank.
this will not be possible in the long run, since knifefish are rather greedy predators.
It did not eat any of the smaller fish yet, but I am afraid this will happen once it grows bigger.
This will certainly happen! However, you can keep this species together with fish that are not regarded prey due to their size.
I also read that this species permanently emits slight electric impulses, how do these affect the other fish?
According to observations so far it affects them hardly or even not at all; knifefish do not use the electric impulses for stunning/killing prey (as electric eels, electric catfish and electric stingrays, among others, do), but for orientation (similar to Mormyrids/Elephant Nose Fish).
And can I still keep it in this tank at all once it reaches its final size of 50 cm?
A larger, in particular longer, tank is very advisable (I recommend at least 2 meters for adult specimes, preferably more).
Then I also read that these fish do not like water changes. I had carried out two in the meantime, I did not notice it affected him...
A water change does not cause harm if carried out correctly, it is just the other way round. However, drastic variations are indeed not well tolerated by rather a lot of species. If "adding fresh water" means something like "70 % water change every 8 months" (and this is sometimes indeed the case, at least in older literature): This can indeed cause trouble with some fish species, among others due to the almost always drastically lower salinity of the freshly added water which can cause an osmotic shock. Regular water changes (e.g. 20 % weekly) help avoid such variations. Larger partial water changes with cooler (not: ice cold!) water can even induce spawning in case of some species (Corydoras catfish!) - such water changes give the fish the impression that the rainy season has begun.
A plea to the readers:
Just like other animals, fish should never be given away as gifts without previous consultation, even if this spoils the surprise. It often happens in such cases that aquarists and pond keepers cannot proceed correctly (e.g. because no suitable quarantine tank is shortly available, or the fish rceived as a gift is not compatible with the other ones, also the party is in full swing, etc.). "To surprise someone" also means not to give the receiver a chance for preparation, and that is certainly never the correct way with live animals.
It is even worse (and such cases have actually been reported, mostly this happens to Koi pond keepers) to secretly put fish into the pond and surprise the receiver (who is supposed to discover an unexpected fish in his pond in the next day and be happy about it) this way. This has led to complete losses of very valuable (intangible and material) Koi stocks due to disease outbreaks (e.g. by newly added Koi that had the Koi Herpes Virus, KHV, in them) - and that can never be intended with a gift that is supposed to create joy.
However, there is a very good alternative if you want to give away an aquarium or pond gift: gift vouchers or possibly earmarked cash gifts! This is not ficticious or bad style - I received both myself in the past, enjoyed it very much and consider this the best solution for all involved (and that of course includes the fish).
Dr. Bodo Schnell