image courtesy of Ed @ photosynthesis
Family
Characidae
Origin
Exodons were originally discovered widespread throughout the Amazon basin and in the Orinoco basin, also in South America. Widespread throughout the Brazilian Amazon basin and has also been recorded in the Rio Branco in Guyana.
Habitat
Usually found in parts of rivers flowing through savannah-like grassland. These biotopes are characterised by flowing waters over sandy substrates.
Maximum Standard Length
It has been claimed that in the wild exodons are known to grow as big as 6", however, this has yet to be proven. you will rarely see them larger then 3" in an aquarium. 4" is considered XL (and unusual) in a home
aquarium. In my studies, I have yet to find any evidence of an exodon larger than 4". It is the opinion of myself and many professionals, some of which have worked with this species in the wild, that the average full grown exodon size is around 3.8"
Minimum Tank Size
A 30" - 36" tank is suggested to house a shoal of these. In anything smaller, however it really depends on
how many you plan to stock. it is possible to keep them in a smaller set up, but it takes a lot of work, and is not recommended to novice keepers. your best bet is to stick with around 3g per inch.
Tank Setup
A biotope setup would consist of a substrate of sand with perhaps a few driftwood branches and roots added for effect. However, the fish look most
effective when kept in a heavily planted tank. This kind of setup has the added benefit of containing plenty of refuges where individuals can go and
seek some respite if they are being singled out for bullying. Filtration should be very efficient to cope with the fact that the species needs to be
maintained in large groups.
heres an example of a natural biotope for this species as done by Heiko Bleher
Temperature
exodons thrive in tropical temperatures of 78-82°F, however, they are pretty tolerant when it comes to temperatures as low as 70°, and over 85°.
PH Range
exodons can be naturally found at the range of pH 5.7 - 6.2, but can be found closer to ph 7 in home aquariums. this is a hardy species that is
easily acclimated.
Hardness
0-20°H
Coloration
Exodons are little fish with brilliant coloration. The caudal fin is yellow and the other fins are red to red tinting. Two very large dark
spots, one in the humeral area in front of the dorsal fin level and the other one covering the whole height of the caudal peduncle are the main
characteristics of this species. they often have a slight blue to purple tint over their entire body, with the females looking more yellow.
Diet
Gut analyses of wild specimens have shown that the diet consists largely of insects and the scales of other fish. Thankfully, there's no need to
provide live fish in captivity, as dead alternatives are readily accepted. Feed a varied diet comprised predominantly of meaty fare such as bloodworm,
chopped prawns, mussel, earthworms and lancefish. Most will even accept dried foods. Ensure any tankmates are receiving enough food, as Exodon are
violent and greedy feeders. Apparently, locals living in areas where the species is common place dirty pans and dishes into the water and the fish
perform a useful task by picking every scrap of food from them!
Compatibility
These fish are found in the same areas inhabited by Fire Tetras (Hyphessobrycon amandae), Red-eyed Moenkhausia (M. oligalepis), two Corydoras species
(Corydoras cf. julii and C. cf. nanus), small sucking catfish (Otocinclus cf. affinis). when kept in groups, these will be fine to keep with exodons.
This is not a community fish, and is best kept in a species setup. It will relentlessly attack any silver-coloured or shiny tankmates, stripping them
of scales and fins very quickly. Even larger, predatory species are not safe. Scaleless and non-reflective fish are generally left alone. Success has
been had keeping Exodon alongside various loaches, Loricariids and some larger characins such as Anostomus. The situation will always be somewhat
unpredictable though. It's best to add the Exodon last as they may see any new additions as food, and as with most predatory species they tend to bite
first and ask questions later.
Make sure you buy a sufficiently large group of these. A minimum of 8-10 is usually recommended, but buy as many as the tank can house. Generally, this
is not a cheap fish at an average price of $7-8/ea (but you can sometimes find them as low as $3-4 if youre lucky). As they need to be kept in larger
groups, be prepared to lighten your wallet a bit if you plan to keep exodons. In a tank like the one described above a group of 25-50 would not be an
unreasonable number, and if you If kept in smaller groups, they tend to pick one another off until only a single fish remains. and a single exodon will
likely die of the stress from being alone. In large shoals, no individual can be targeted and it is usually only sick or unhealthy specimens that are
killed, although occasional losses should still be expected. The interaction of a big group is fascinating to watch, as they squabble amongst themselves
constantly. Feeding time in particular is quite a sight.
Buy the entire group at the same time as new additions are usually attacked. However if you decide to add to your shoal after the initial group, you will
want to add them in a group of 5 or more, as a single introduced fish may be seen as food and killed before morning. It is also suggested that you do a
Water change prior to adding the new exodons to the tank, this will help to distract the shoal.
Sexing
Mature males are slimmer than females, who tend to be broader and wider, and tend to have slightly elongated dorsal and anal fin rays.
Breeding
Has been achieved, but rarely. It's an egg scattering species. The best way to approach a breeding project is to set up a separate tank in which to
spawn the fish. Something around 24" x 12" x 12" in size should be sufficient. This can be empty save for some clumps of fine-leaved plants to catch
the eggs. Alternatively, cover the base of the tank with marbles or similar round stones. This should be big enough so that fish eggs can fall through
it, but small enough to prevent the adult fish from reaching them. Water should be soft and slightly acidic (pH 6.0-6.5, gH 1-5). Meanwhile, condition
the adults in a shoal in a separate tank, as described above.
Once the fish are in good condition, select a pair and transfer them to the spawning tank. this can take a few tries as its difficult to determine weather
or not a breedig pair has been established. Apparently spawning can sometimes be initiated by performing a large (50%+) water change with slightly warmer
water than that in the tank. Remove the adults as soon as eggs are noticed, as they will eat their spawn given the opportunity.
The eggs hatch in as soon as 48 hours and up to 3 days. There is little information available regarding raising of the fry. It's likely that small livefoods
such as newly hatched brineshrimp will be accepted. Cannibalism will probably be rife, so keep a close eye on the young as they grow and have several tanks
ready to move differently sized fish into.
Other Notes
The genus Exodon is currently monotypic, with this single species having uniquely designed teeth. The mouth of the exodon is terminal and scarcely
oblique; its premaxilla, which has an ascending process, has 3 outer tusks and 6 inner acute; the maxilla bears a tubercle near its joint and 9 or 10 acute
teeth, the latter ones pointing outward. The mandible has 4 external tubercles, the foremost one pointing forward, and an inner series of about 17 small
conical teeth of the characid type. These allow it to rip the scales from other species.
It's an ideal choice for those wishing to keep a large shoal of a predatory species without possessing the massive amount of tank space needed for a
shoal of piranha or similar. A tank full of these makes for a very colourful and active display.
