Serrasalmus marginatus

Classification

Characidae. Subfamily: Serrasalminae

Distribution

Has been recorded from Brazil, Paraguay, Uruguay and Argentina, occuring in the Rio Paraguay and Rio Paraná drainages.

Habitat

It inhabits rivers, pools and creeks, apparently showing a preference for shady areas with dense marginal or submerged vegetation. Apparently individuals defend “feeding territories” of up to 4 square metres.

Maximum Standard Length

8.7″/22.1cm.

Aquarium SizeTop ↑

A 48″ x 15″ x 15″/120cm x 37.5cm x 37.5cm/177 litre tank could house one of these for life.

Maintenance

Best kept in a planted set-up with plenty of shaded areas. A wild-looking tank decorated with tangles of roots and branches, clumps of plant species that grow to the water surface, patches of floating vegetation and a dark substrate is ideal. Don’t be surprised if the fish nips at the plants a bit as many some members of the genus are now known to be omnivorous animals. You can keep it in a barer set-up if you prefer, but individual fish vary in character and some may behave nervously in this type of environment.

Water quality must be of the highest order for this fish to thrive, and a moderate rate of flow seems to make it happier still. Use an external canister-style filter or sump, arranging the pipework so that water is returned lengthways along the tank. Place the spraybar so that it agitates the water surface a little. Additional powerheads are recommended by some sources but are not necessary if the tank is set up correctly. As usual when keeping large, predatory species weekly partial water changes of up to 50% are a must.

If possible the heaterstat should also be situated externally, as serrasalmids been known to attack both these and other items of equipment when they are located inside the tank. It’s possible to buy external filters with built-in heater elements, or inline units that can be fitted to the filter pipework. Failing these a sturdy heater-guard should be considered a minimum requirement.

Water Conditions

Temperature: 72 – 77°F/22 – 25°C

pH: 6.5 – 7.0

Hardness: 5 – 15°

Diet

Wild fish feed mainly on the fins of other species as well as smaller fish, insects and crustaceans. Small amounts of plant material have also been found in the stomach during laboratory analyses, and amazingly it has been observed removing parasites from the bodies of larger red-bellied piranha (Pygocentrus nattereri). When hunting it uses stealth, approaching potential prey slowly before darting in and nipping off a piece of anal or caudal fin.

In the aquarium most individuals can be weaned onto dead foods over time, although some seem to find it trickier to adjust than others and may refuse to feed initially. A period of starvation may be necessary, eventually giving the fish little choice but to accept what is offered. This is especially true of larger or recently-transported specimens.

Once acclimatised juveniles relish live or frozen bloodworm, Tubifex, Artemia, chopped prawns and similar foods. Adults should be fed correspondingly larger items, such as whole mussels, cockles, prawns, chopped squid, whitebait and earthworms. Once the fish reaches adult size it need only be fed two or three times a week.

This species should not be fed large amounts of mammalian/avian meat such as beef heart or chicken. Some of the lipids contained in these meats cannot be properly metabolised by the fish, and can cause excess deposits of fat and even organ degeneration. Similarly there is no benefit in the use of ‘feeder’ fish such as livebearers or small goldfish. Risks involved with these include the possible introduction of disease or parasites.

Behaviour and CompatibilityTop ↑

Should only be considered as a specimen fish for the enthusiast. This species doesn’t make a good tankmate for anything else. Scattered reports of it co-existing with other species should be considered tenuous at best given its natural diet. Similarly there is little point attempting to keep two or more of these together. It is not a gregarious animal by nature and conspecifics are liable to fight until only one remains.

Sexual Dimorphism

Unknown.

Reproduction

Not thought to have been spawned in aquaria.

NotesTop ↑

There are currently 24 described species of Serrasalmus, many of which look superficially similar. S. marginatus has at various times been considered a synonym of S. rhombeus and S. humeralis, but is currently considered to be distinct. It’s main distinguishing feature is usually given as the thick, black, v-shaped marking in the anterior portion of the caudal fin. Juveniles are said to differ from similar-looking species such as S. compressus and S. altuvei because the dark body “spots” are always oval/rounded in appearance and never bar-shaped. It’s rarely seen in the hobby and is highly-coveted by enthusiasts as a result.

Most experts agree that a detailed revision of Serrasalmus is necessary, as historically the genus has been viewed as something of a “catch-all” for similar-looking fin-biting/predatory characins. The juvenile forms of numerous species look broadly similar, characteristically developing the more distinctive adult patterning as they mature. This has resulted in new species being erected erroneously and there have been several attempts to reorganise the group. The most recent major revision was undertaken by Géry in the late 1970s, but a handful of new species have been described since then.

It’s worth noting that in South America only Pygocentrus species such as the infamous red-bellied P. nattereri are known as piranha, with Serrasalmus and other related genera being referred to by other names such as Pirambeba. Serrasalmus species are therefore not considered to be “true” piranhas, the name being applied to them by the English-speaking world and aquatic hobby. The relationship between these genera is too complex to address here, although when observing mature fish clear morphological differences are apparent. In his 1991 revision of Pygocentrus Fink stated the following:

“Relative to other serrasalmin, Pygocentrus is diagnosable by several features, including prepelvic serrae number, morphology of the gas bladder and skull, and head width.”

It should also be said that serrasalmids are not the fearsome “monster fish” as often depicted by the media. Obvious care must be taken when performing tank maintenace but these fish will usually only bite when threatened, and they can be quite skittish in an aquarium setting unless their rather specialist needs are catered for. Most also live in excess of ten years and become less active as they mature, so think carefully before buying one.