The Emperor Tetra By Hans de Vries
The Emperor Tetra (Nematobrycon palmeri) became available to aquarists after the Second World War. Its main habitat is the San Juan River system in Columbia. As soon as it was introduced it became a very popular species.
It grows to about 7cm in length with the male being the larger. The basic coloration is brownish to salmon which under bright light becomes iridescent green or bluish purple. A black line runs from the eye to the central part of the three-lined tail fin. The male has longer central tail fin rays. Another important difference between the sexes is the colour of the eyes which are blue for the male and green for the female. This feature can be used to distinguish the sexes when in their juvenile stage. Besides it's attractive colouring, the species has a peaceful nature and is therefore suitable for a community aquarium.
I have kept Emperor Tetras since establishing my first tropical freshwater aquarium in Australia in the late 1960's. I started with two pairs who shared the tank with other Tetra species (Cardinals, Glow-Lights, Black Neons, Serpae and Lemon Tetras). The tank was always densely planted mainly with Cryptocorynes, Sword Plants, Ambulia and Ludwigia species. Soon after being placed in the tank the two males commenced mirror fights to determine dominance. After a week or so I discovered that one of the males defended a very densely planted corner of the aquarium against any intruders. After a further two weeks I noticed fry swimming amongst the plants near the water surface. Today, I still have Emperor Tetras. They have maintained themselves in the community aquarium. Sometimes only 3 to 5 juveniles survive, at other times 10 to 12.
As I was somewhat concerned about inbreeding, I purchased another two males in the late 1970's. I have not observed any phenomena associated with inbreeding to date. It should be recognised however that breeding in a community aquarium results in many eggs and fry being taken by other fishes and only the fittest survive. It is also not very productive.
The water conditions are not critical for Emperor Tetras. Ideally, my Tetra tank is kept slightly acid with water being fitered over peat (the new blackpeat granules are recommended). On occasions the pH has been as low as 5.4. Shellgrit put into the filter system or a small handful put into the tank ensures that the pH increases, sometimes up to 7.8. Because of these fluctuations, I now follow the strict rule to change 1/4 of the water weekly, which has resulted in a much more stable pH at the level required by the Tetras.
When fry are observed in the tank, the only extra food given are any of the micron foods and freshly hatched Brine Shrimp for a period of 5 to 6 weeks after which the normal variety of flake foods and freeze dried and frozen foods are given with some live foods when available.
There are two related species available also originating from Columbia, but each from a different river system. One species is much lighter in colour and the other darker with a fuller body than the Emperor Tetra. It is likely that the three species have evolved from the same forebears.
It would be interesting to obtain some comments from members regarding aspects of inbreeding of fish.
Editor's Note: This is the second Emperor Tetra article in as many issues, but I feel that it is important to get as many different angles on our commonly-kept species as possible. I can vouch for the fact that Emperors (and Kerri Tetras) will successfully spawn in a community tank, unlike some of their more ‘delicate’ cousins, albeit nowhere near as well as a good spawning setup in a seperate tank.
On inbreeding, this affects the two main groups of fishes that Julie and I have always kept, Cichlids and Rainbowfish. Both contain species not native to Australia that are not allowable imports (Australian Rainbowfish 'blood' can be freshened by Safari using several hundred dollars worth of petrol and a Land Cruiser, but this is not a journey to be undertaken lightly. You can't do this for the New Guinean species.) and basically, what we have is all we will ever get.
Inbred Cichlids have deformed mouths, kinky fins, washy colour, and basically aren't worth feeding. Inbred Rainbowfish seem prone to ulcers, as well as suffering from the aforementioned deformities. What do you do? Only breed from deformity free adults, try and get the parents from different sources (even if you are working with a species that is descended from only four specimens brought into Australia, there will still be local variations in keeping/feeding/temperature methods to ensure a little more genetic diversity than breeding brother/sister from your own tanks), and cull deformed youngsters mercilessly. If you can only obtain deformed stock to begin with, try spawning them anyway if they are extremely rare, because they are descended from deformity-free stock (in the wild) and may produce a couple of fry better than themselves. This means the harsh process of culling most of the youngsters, which shouldn't really be the point of any spawning.