Serrasalmus maculatus

Mac

Classification

Serrasalmidae

Distribution

Described from the rio Guaporé in Mato Grosso state, western Brazil but now considered widespread in the Amazon, paraguay and Paraná river systems in Colombia, Peru, Brazil, Bolivia, Paraguay, Uruguay and Argentina.

Habitat

Inhabits rivers, pools and creeks, apparently showing a preference for shady areas with dense marginal or submerged vegetation. It’s been observed to occur in small groups (~20 individuals) each of which appears to patrol a given range.

Maximum Standard Length

180 – 210 mm.

Aquarium SizeTop ↑

An aquarium with base dimensions of 120 cm x 45 cm or more is required for a single adult with much larger quarters required for a group.

Maintenance

Requires a well-oxygenated set-up, ideally furnished with a sandy substrate and some driftwood roots and branches to provide cover. You can attempt to grow aquatic plants if you wish but don’t be surprised if the fish nip at them. Water quality must be of the highest order meaning weekly water changes of up to 50% should be considered mandatory.

If possible the heaterstat should also be situated externally since serrasalmids do sometimes bite equipment located inside the tank. It’s possible to buy external filters with built-in heater elements or inline units that can be installed the filter pipework, or at the very least a sturdy heater-guard should be fitted.

Water Conditions

Temperature: 70 – 86°F/21.1 – 30°C

pH: 6.5 – 7.5

Hardness: 5 – 15°H

Diet

Wild fish are opportunistic, feeding on the fins and flesh of other species as well as smaller fishes, insects and crustaceans. They have also been recorded scavenging the carcasses of dead animals including humans although reports of this species attacking live people are mostly attributed to increased aggression during the breeding season.

Some Serrasalmus have been shown to eat nuts, fruits and seeds and small amounts of plant material have been found in the gut of S. maculatus during laboratory analyses. 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 which carry with them the risk of parasite or disease introduction and at any rate tend not have a high nutritional value unless properly conditioned beforehand.

Behaviour and CompatibilityTop ↑

Should only be considered as a specimen fish for the enthusiast since it doesn’t make a good tankmate for anything else. Scattered reports of it coexisting with Loricariids, armoured catfish and in conspecific groups should be considered tenuous at best given its carnivorous nature.

The issue of whether or not S. maculatus can be kept in groups remains hotly-debated among enthusiasts. Some argue that the species should always be considered unpredictable in a closed environment such as an aquarium, the risk of injury outweighing any positive consequences of cohabiting these fish. Others meanwhile have successfully maintained quite large groups of the species, in some cases for considerable periods of time. We recommend keeping it singly, reserving such experiments for those aquarists with many years’ experience and the resources to provide the necessary tank space.

Sexual Dimorphism

No external sexual differences between the sexes have been recorded although females in spawning condition are usually plumper than males.

Reproduction

S. maculatus is a continuous (as opposed to seasonal) spawner in nature and is considered one of the easiest members of the genus to breed in aquaria. Please note that this is not a project for the average hobbyist. Several large tanks might be required for maintenance, conditioning and spawning of adults as well as raising what may number over 1000 fry.

A particularly detailed account by Japanese aquarist Hiroshe Azuma was published in the American magazine Tropical Fish Hobbyist in 1990. He successfully bred the species using a large (in excess of 750 litre), heavily planted tank containing a group of mature adults. The water was soft and acidic and the temperature towards the upper end of the recommended range above.

When in spawning condition females were noted to swell noticeably in the belly. Both fish would darken in colour, but the male tended to do so first and with greater intensity. When a pair was noticed they would be removed and conditioned individually, away from the main group. After two weeks the male was added to a further planted set-up, to which the female was introduced 24 hours later. Some males would attack the female during courtship and spawning, causing quite severe injuries in some cases while others were more peaceful. The amount of time that passed before spawning occured also varied, with some males showing immediate interest in the female and others taking 10 days or more. Almost all spawning events occured within a period of 18 days.

Prior to the act itself the male was observed to select a spawning site bite small pieces from surrounding vegetation though these were not consumed and the precise reason for this behaviour remains unclear. Courtship and spawning took around 3 hours with the fish repeatedly coming together over the spawning site. The male was seen to curl his anal fin under the body of the female which was presumed to facilitate a better ratio of egg fertilisation.

The adults were removed post-spawning. An average brood numbered between 800 – 1200 eggs, these hatching in 54 – 58 hours at 82°F/28°C. The fry were free swimming within a week and raised on Artemia nauplii, Tubifex and bloodworm.

In nature the male guards the eggs until they hatch. Other hobbyists have recorded such behaviour when the parents are left in the tank post-spawning with the male becoming very aggressive towards anything approaching the “nest”. Success has also been had using relatively small volumes (< 200 litres) of water and without moving the fish between different aquaria.

NotesTop ↑

S. maculatus is one of the better choices for aquarists new to this group of fishes. It grows to a manageable size, is relatively hardy, attractive and usually quite inexpensive. It’s sometimes referred to by the alternative vernacular names “gold piranha” or “golden mac” in the hobby.

There are in excess of 30 described species of Serrasalmus many of which appear superficially similar and have confusing taxonomic histories. S. maculatus and S. spilopleura have often been confused in the past, but can be separated by the following characters: infraorbital series bones wider in S. maculatus vs. narrower in S. spilopleura; naked cheek zone narrower vs. broader; possession of subterminal black bar in the caudal fin vs. distal portion of caudal fin hyaline. This conclusion remains in dispute with claims that mistakes were made in the review of the species by Jégu and Dos Santos (2001), but it remains unclear what those purported errors are.

Most experts agree that a detailed revision of Serrasalmus is necessary since historically the genus has been viewed as something of a “catch-all” for similar-looking fin-biting/predatory characins for decades and has long-been regognised a polyphyletic grouping. There have been several attempts to reorganise the group with the most recent major revision published by Géry in the late 1970s but a handful of new species have been described since then and an exhaustive molecular analysis of member species remains lacking.

The family Serrasalmidae consists of over 60 species in 16 genera and also includes the seed and fruit eating tambaquis and pacus among others. Their characteristic features include a compressed body shape, long dorsal fin with 16 or more rays and possession of sharp serrae on the ventral surface formed by modified abdominal scales. The number of the latter is variable, ranging from 6-9 in Acnodon to over 60 in Piaractus spp..

Members display three main feeding habits: carnivory (flesh-eating), frugivory (fruit and seed-eating) and lepidophagy (eating the scales and fins of other fishes). Carnvirous species normally possess a single row of tricuspid teeth on each jaw, frugivores tend to have two series of incisor or molariform teeth on the premaxilla, one row of teeth on the dentaries, and often a pair of symphyseal teeth, while in lepidophages the teeth are tuberculated and located on the outer side of the premaxilla.

Based on the results of their mitochondrial DNA-based phylogenetic analyses of serrasalmids Ortí et al. (2008) recommended that member genus Pristobrycon be restricted to contain just the single species P. striolatus with all other members placed in Serrasalmus, to which they are more closely-related, but this concept appears not to have achieved general acceptance at time of writing.

In South America only Pygocentrus species are referred to as “piraña“, 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.

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 careful thought is required before purchasing one as they represent a considerable investment.