Extreme Characins 

As we saw last month, characins are a lot more diverse than many people assume, with a variety of shapes and sizes that easily matches that of more celebrated groups like the cichlids and catfish. For the aquarist interested in oddball fish, characins are a very rich seam indeed.

Many of the more unusual characins are small and harmless little creatures; into this category fall things like the Pencilfish. These fish eat only tiny invertebrates such as insect larvae, and are more likely to be bullied by their tankmates than to cause mischief. Others are larger and though herbivorous, are territorial enough that tankmates need to be chosen with care. The Headstanders of the family Anostomidae definitely number among this type of characin, and need to be handled in much the same way as a territorial cichlid. Finally, there are the characins that are both large and predatory, and these are the species that need to be handled with the greatest degree of care. Some can actually make very good community fish, provided their tankmates are too big to be considered potential meals, but others are so nefarious in their habits that they cannot be mixed with anything. In this article, we'll look at predatory characins that fall into both camps.

Wolf-characins, family Erythrinidae

The wolf-characins, or Trahiras, are a small family of very distinctive characins. Unlike the majority of characins, these fish lack an adipose fin. They are also able to breathe air, allowing them to survive in pools and ditches where other fish cannot, and if things get too dire, they are even able to make short excursions across land to find somewhere more hospitable. Another distinctive feature of this group is that the males build a nest and either alone (or, less commonly, with the female) protects the eggs and fry.

The red wolf-characin, Erythrinus erythrinus, is one of the smallest species of its type regularly offered for sale, and arguably the best all-rounder as far as aquarium maintenance goes. The average specimen is pale greenish-pink fish with a dark band running along the midline of the fish and a distinctive shiny spot on the gill covers. There are usually orange markings around the throat, belly and the base of the tail, though these tend to fade on mature specimens. In recent years though, the 'high-fin red' or 'rainbow' variety has become more firmly established in the trade, sometimes under the name Erythrinus sp. 'Peru'. It has a tall dorsal fin marked with reddish-orange. The tail fin is similarly marked, and there are usually additional colour markings on the flanks and sometimes the anal fin as well. Red wolf-characins grow to a maximum size of about 20 cm/8" in the wild, though aquarium specimens tend to be somewhat smaller. Although they are very aggressive towards one another, dissimilar tankmates, such as large barbs and catfish, are generally ignored.

A similar species is the aimara Hoplerythrinus unitaeniatus, distinguished by its larger size (up to 40 cm/16") and the bold horizontal band running along its body. Both these wolf-characins feed primarily on invertebrates in the wild, rather than fish as is popularly assumed, and for optimal health they should be provided things like earthworms, river shrimps, and large aquatic insects. Frozen substitutes are enjoyed as well. Quite different is the trahira Hoplias malabaricus, a fish that feeds on invertebrates when young but as it matures becomes increasingly piscivorous. That said, is adaptable and easily trained to take frozen lancefish and whitebait, though some variation in the form of worms, shrimps, and other invertebrates is probably a very good idea. The main problem with the trahira is its size: at up to 50 cm/20" in length it is only suitable for maintenance in very large aquaria. The combination of large size, snappy disposition, and predatory nature mean that this fish cannot be easily kept with tankmates except perhaps the very largest and most heavily armoured catfish.

Oddly for animals so well adapted to living in difficult environments, the smaller wolf-characins in particular have not proved to be especially hardy. Good water quality, and soft to moderately hard, not too alkaline water seems to be essential. Since these fish like to stay close to cover, a tank that is not too strongly illuminated and planted with Java fern or Anubias attached to bogwood would suit them perfectly.

Payara: the vampire-tetra!

Where the wolf-characins were adapted to life in sluggish streams and pools, the family Cynodontidae contains a small number of species that are exclusively found in clean, fast-flowing rivers. All have robust teeth and among scientists these fish are called dogtooth tetras, but the two species offered to aquarists are usually called vampire-tetras on account of their protruding fangs. The two species sold appear to be Hydrolycus armatus and Hydrolycus scomberoides, though many retailers treat them as one and the same thing. The two fish are broadly similar: big, silvery, very streamlined and powerful, and with distinctly upturned jaws. Hydrolycus armatus is smaller (potentially getting to around 60 cm/24" in length) whereas Hydrolycus scomberoides can get to twice that size, but otherwise the only obvious difference is in the shape of the dark marking behind the gill covers. On Hydrolycus scomberoides this marking is approximately circular, whereas on Hydrolycus armatus it is a short, oblique bar.

It is actually quite debatable whether vampire-tetras are good aquarium fish.  They are obviously very big fish, and both require perfectly clean and well-oxygenated water, so frequent water changes and generous levels of filtration are the order of the day. Water chemistry requirements are typical for Amazonian whitewater fish: a neutral to slightly acidic pH plus low to moderate hardness. In the wild vampire-tetras are often found in groups, but in captivity when kept in small groups they are antagonistic towards one another, to the point that the dominant specimen eventually bullies conspecifics to death. On the other hand, single specimens often seem to be nervous and when scared will throw themselves around the tank frantically, damaging themselves in the process. Realistically, you probably need to keep a group of at least six specimens to stand anything like a good chance of the group forming a stable, happy school. Obviously setting up a tank for six active fish the size of vampire-tetras isn't something to be done on a whim. In addition, any tankmates from other species should be chosen with care. Placid armoured catfish would be ideal tankmates, but anything too aggressive, such as large cichlids, would be unwise.

As far as food goes, these fish are out-and-out piscivores. Vampire-tetras feed on schooling characins in the wild (including piranha!) and in captivity are most easily reared using live foods such as earthworms, river shrimps, and clean feeder fish. They can be weaned onto dead foods, such as silversides and lancefish, though this does take time. One final note: although these fish are fairly widely sold and seem to settle into aquarium life quite easily, they do not seem live nearly so long in captivity as in the wild. Many aquarists find that these fish do well for six months of a year, and then die for no obvious reason. Diet, water conditions, and their schooling behaviour may all be key factors, and any aquarist attracted to these fish should research them fully before bringing them home.

The African fin-eating tetras

Also known as the African pike-characins, the genera Belonophago, Paraphago, and Phago are fascinating subjects for the aquarist after a bizarre predatory characin but without the space to accommodate something like a school of vampire-tetras. They are all fairly small animals, and none is terribly active. The smallest species are in the genus Belonophago and around 10 cm/4" when fully grown; the remaining species are about half as big again. Apart from size differences, telling the species apart isn't easy as they are all pretty similar. They have a slender, pike-shape and distinctive tail fins that bear striking horizontal black bands. These fish are fairly cryptic in their colouration, being silvery green with some sort of mottling or banding along the body and on the fins. Given the choice, these fish prefer to stay hidden among the shadows than in open water, and just like our own native pike, these fish are stealth predators that will snap at any suitably sized prey, from aquatic insects through to smaller fish.

While there are many predatory characins, these fish are unusual in having scissor-like upper and lower jaws that can easily snip the fins off fish too large to swallow whole. Obviously, since they will eat small fish whole and large fish a bit a time, African pike-characins cannot be easily mixed with other fish, though heavily armoured catfish such as Doradids and Loricariids might be an option.

African pike-characins are members of the characin family Citharinidae, of which there are numerous species offered more or less regularly to aquarists. Most make excellent aquarium fish. Nannaethiops unitaeniatus is sometimes sold as the African Glowlight tetra, an allusion to the attractive coppery band running along the flanks of this fish that gives it a superficial resemblance to the popular Glowlight tetra from South America, Hemigrammus erythrozonus. The African Glowlight is a peaceful, schooling species that gets to about 6 cm/2.5" long and does best in a quiet, well-planted aquarium with soft, slightly acidic water. At the other end of the size spectrum is Distichodus sexfasciatus, a large, deep-bodied characin that has, at least when young, the same brilliant orange and black colouration of the clown loach and tiger barb. Adults can potentially reach over 70 cm/27" in length, though aquarium specimens rarely get to even half that size. Adults are also somewhat less colourful than the juveniles, though attractive fish nonetheless. These fish omnivores, and will as readily eat lettuce and peas, as they will bloodworms and brine shrimp. Needless to say, they will demolish a plant aquarium in no time at all.

Freshwater barracuda, family Acestrorhynchidae

Freshwater barracuda have become quite common imports in recent years. Despite their name, these fish are not true barracuda but characins in good standing. All the currently known species are in a single genus, Acestrorhynchus, of which more than a dozen species are known ranging in size from 7 to 40 cm/2.75-15". Unfortunately for the aquarist, the more commonly traded species seem to be the bigger species rather than the smaller. In particular, Acestrorhynchus falcatus (27 cm/10.5") and Acestrorhynchus falcirostris (40 cm/15") seem to predominate.

As their streamlined shape and powerful jaws might suggest, these fish are predators, and that's the problem: these fish are not easily weaned onto anything other than live foods. Earthworms, river shrimps, and other robust invertebrate foods are preferred, though small prey like bloodworms may be taken as well, depending on the size of the fish. Despite their predatory nature, most species of freshwater barracuda are nervous and do best kept in a small group in a spacious aquarium with plenty of swimming space and plants around the edges. Floating plants, or at least plants with long, trailing leaves, such as giant Vallisneria, are greatly appreciated. Tankmates need to be chosen with care as freshwater barracuda are easily frightened.

Freshwater barracuda are often confused with the African pike Hepsetus odoe, an only-distantly related characin. Hepsetus odoe are big fish in the wild, getting to around 70 cm/27" in length, making them far from ideal aquarium fish. They are also exceptionally powerful fish with a very nervous disposition, and can easily damage themselves when alarmed by throwing themselves against the glass of the tank. Though barely suitable for maintenance in a home aquarium, these animals to make outstanding exhibits in public aquaria where they have space to settle in more comfortably.

Sidebar: Little jewels -- small but fascinating oddball characins

There are lots of small oddball characins as well. Among the most interesting is the swordtail characin, Corynopoma riisei (4.8 cm/1.9"). This characin is unique in practising internal fertilisation; the eggs of all other characins are fertilised externally, with the male shedding milt over the eggs as they are deposited on the substrate or among plants. Female swordtail characins carry the fertilised eggs for more than 24 hours after mating, and so are able select the site where the eggs are deposited more carefully. Swordtail characin males live up to their name by having greatly extended fin rays on the lower half of the tail fin. Though not brightly coloured, these fish are lively and attractive, and make excellent community tank residents. They are schooling fish and very gently in temperament, and are best kept with other small characins, Corydoras, and peaceful dwarf cichlids. Swordtail characins have a reputation for being delicate immediately after import, but once settled in adapt readily to aquarium life and have proven to be long-lived and fairly hardy animals.

The darter characins of the genus Characidium are splendid little oddballs for the community aquarium. Several species are traded, but they're all pretty similar and retailers rarely distinguish them. Characidium fasciatum and Characidium ranchovii are perhaps the two most widely sold, and at first either could be mistaken for a sucking loach or Siamese algae eater. Characidium fasciatum (10 cm/4") can be distinguished by a criss-cross pattern of short vertical bands set against a thick horizontal stripe running along the flanks. Characidium ranchovii (7.5 cm/3") on the other hand, is mostly unmarked except for a think dark band that runs along its midline. Unlike most characins, these are benthic fish that scoot about the bottom of the tank foraging for small invertebrates such as bloodworms. In aquaria, they are peaceful, non-territorial fish that adapt quickly to dry and frozen foods of suitable size. In terms of water chemistry, these fish prefer soft, slightly acidic water, and most critically the water should be clean and well oxygenated.

While a little larger than the other small oddballs mentioned here, Exodon paradoxus is at least regularly traded, lively, and very attractive. Known as the bucktooth tetra in the hobby, this characin is highly carnivorous and will eat small tankmates. Wild specimens are supposed to reach around 15 cm/6" in length, but aquarium specimens tend to be much smaller, typically 10 cm/4" or less. Maintenance with large community fish is complicated by the fact that these fish not only eat whole small fish but also the fins and scales of larger fish as well. So while some people have had luck combining them with robust fish such as Plecs, the best way to keep them is in their own aquarium. These are intensely hierarchical schooling fish, and if kept in small groups the dominant individuals tends to bully the others, to the point where weaker are damaged or even killed. A dozen or more specimens may be an expensive investment, but only then will the aquarist get to watch their most famous behavioural trait: the feeding frenzy! Pretty much anything meaty is eaten, from flake and pellets through to frozen bloodworms and lancefish.