Heckel Discus

Geographical Origin & Biotope:

The *Symphysodon discus* (Heckel) is endemic to the most extreme basins of the Amazon system: it is the undisputed king of the Rio Negro, the largest blackwater river in the world, and its tributaries (Rio Abacaxis, Rio Trombetas). These waters are characterized by a very high concentration of humic and fulvic acids, derived from the decomposition of the gigantic flooded rainforest. Here the water is the color of very dark tea, the pH is prohibitive for most pathogenic bacteria, and the load of dissolved minerals is almost zero.

Taxonomy & Morphology:

The genus *Symphysodon* is characterized by its perfectly discoid and laterally extremely compressed shape (an extreme adaptation for moving vertically through the dense tangle of roots without hitting lateral obstacles). The Heckel is a distinct species and not a color strain of common domestic discus (often complex hybrids of *S. aequifasciatus* and *S. haraldi*). It reaches 20 cm (8 inches) in diameter. The teeth are very reduced, located only near the maxillary symphysis.

Social Behavior:

They are profoundly gregarious fish and must be kept in schools of no less than 6 individuals. Within the group, a strict but bloodless pecking order is established. The introduction of a new specimen into an already established school will result in weeks of hierarchical squabbles, often resolved by slapping their flat flanks against each other as a form of muscular intimidation. Pairs tend to isolate themselves in a hypnotic mating dance.

Coloration & Sexual Dimorphism:

The livery of the true Heckel Discus is unmistakable. It possesses 9 dark vertical bars on its body (like other Discus), but the unique feature is that the first, fifth (central), and ninth bars are enormously thicker and markedly black (the central band, in particular, stands out sharply). The background varies from dull blue-green to brownish, crossed by wavy electric blue striations on the snout, back, and peduncle. Sexual dimorphism is absent and unobservable outside of breeding times.

Tank Setup:

A school of Heckel Discus requires a devoted space. The aquarium must measure no less than 120 cm (4 feet) for about 300 liters (80 gallons). The setup must perfectly replicate an untouched "Blackwater" river: using very fine white sand on the bottom is fundamental as they love to 'blow' on it to uncover food debris. Twisted bogwood roots descending from above and a mattress of Catappa or Oak leaves on the bottom will create a vital sense of security. The light must be very dim and shaded; in overly lit tanks they will lose all their color, constantly hiding in the shadows.

Diet & Feeding:

Feeding Heckels, being almost exclusively wild-caught specimens, is complex. They often flatly refuse commercial pellet or flake foods accepted by their captive-bred cousins. The diet must be started with frozen white and red bloodworms, daphnia, and enriched brine shrimp. Many expert breeders prepare homemade "beef heart mixes" based on beef or turkey heart, shrimp, spinach, and spirulina, although an excess of mammalian protein can cause blockages. It is imperative to feed little and often, removing any leftovers.

Water Quality:

This is the critical aspect par excellence. The Heckel lives in waters whose chemical characteristics are extreme: hardness must be measurable around GH 1-4, carbonate hardness (KH) zero, and the pH should be pushed with peat extracts down to 4.5 or 5.5. Massive water changes (30% every 2-3 days in grow-out tanks) are the only guarantee of perfect hygiene to prevent stunted growth and disease. The temperature must be blistering by normal standards: 28°C (82°F) as a base, 30-32°C (86-90°F) as ideal.

Compatibility & Tankmates:

Being extremely peaceful cichlids but territorially hierarchical among themselves, interspecific interactions are an unnecessary stress. The vast majority of experts keep *Symphysodon discus* in a species-only tank. If an extreme South American community aquarium (Rio Negro biotope) is truly desired, one can add very large schools of Cardinal Tetras or *Hemigrammus bleheri*, which act as dither fish, indicating to the Discus that the area is free of predators. On the bottom, only Loricariids or Corydoras capable of withstanding constant 30°C (such as *C. sterbai*).

Aquarium Breeding:

Keeping the Heckel is very difficult; breeding it is legendary. Spawning occurs in practically distilled water conditions (conductivity under 50 µS) and extremely acidic pH. Once hatched, the larvae have a unique biology: they feed exclusively on an epidermal mucilaginous secretion produced by the parents. The larvae will attach themselves to the flanks of the male and female, grazing on the mucus for weeks. Separating the larvae from the parents means certain death by starvation.

Risks & Diseases:

Stress and imperfect water inexorably translate into Spironucleus or Hexamita (Hole-in-the-head disease and stringy white feces), to which the Heckel is disastrously sensitive due to its weak immune system against closed-system pathogens. Ich is rare if temperatures are kept above 29°C (84°F).