Pterophyllum altum, also referred to as the Altum Angelfish, Deep Angelfish, or Orinoco Angelfish,[1] occurs strictly in the Orinoco River Basin and the Upper Rio Negro watershed in Southern Venezuela, Southeastern Colombia and extreme Northern Brazil.[2] The species is the largest of the genus and specimens exceeding 50 cm in height (from tip of dorsal to tip of anal fin) have been reported in the wild; in aquariums, specimens are known to have grown to over 40 cm. Its natural base color is silver but with three brownish/red vertical stripes and red striations into the fins. The species may show red spotting and a blueish green dorsal overcast when mature and when aroused exhibits a black operculum spot. Characteristic of this species is an acute incision or notch above the nares (supraorbital indention). All true Orinoco Altum specimens show this trait, whereas commercial hybrids product of crosses to Pterophyllum scalare, that are occasionally performed by breeders to sell them as "Orinoco Altum", may not exhibit the trait or it may appear in a lesser degree. The true wildcaught Orinoco Altum is among the most challenging among tropical fish to breed in captivity. Most Altum Angels are more frequently found in the well oxygenated, extremely soft waters of Upper and Middle Orinoco tributaries shed from the Guyana Shield Highlands, preferring a pH range between 4.5 to 5.8. These are very transparent blackwaters with almost nil conductivity. Temperature range in these waters is between 78°F (26°C) and 84°F (29°C). They are also found in the Atabapo River and Inirida River floodplain, down the Casiquiare and Guainía floodplain where the Rio Negro is born, before entering Brazilian territory. Unlike P. scalare(mentioned above) which prefer to spawn on the submerged leaves of plants and trees in the flooded rainforest, P. altum prefers to spawn on submerged roots and tree branches in a moderate water current. This species is recommended for intermediate to advanced aquarists due to the detailed maintenance it requires for proper health. Pterophyllum altum is the national fish of Venezuela and an image of the fish appears on some currency bills of that country.

Care

Angelfish are kept in a warm aquarium, ideally around 80 °F (27 °C). They will do best if fed a mixture of flake, frozen and live food. Care should be taken to not overfeed, they will continue to eat even what they do not need to. This will lead to a buildup of fats resulting in inactivity and early death. Angelfish will do best if kept in an acidic environment, pH should be below 7.5 (note: 7.5 is still slightly alkaline - acidic is defined as below 7.0). All angelfish will prefer water with a pH of at most 7.0. Though most Pterophyllum scalare will thrive in a wide range of pH values. Even though angelfish are a member of the Cichlid family they are generally peaceful, however; the general rule "big fish eat little fish" applies. Aggressive fish should not be kept with angelfish because their flowing fins are vulnerable to fin nipping. Some smaller more aggressive fish may even nip at the fins of these fish.

Breeding

P. altum is notably difficult to breed in an aquarium environment.

Angelfish pairs form long-term relationships where each individual will protect the other from threats and potential suitors. Upon the death or removal of one of the mated pair, breeders have experienced both the total refusal of the remaining mate to pair up with any other angelfish and successful breeding with subsequent mates.

Depending upon aquarium conditions, P. altum reaches sexual maturity at the age of six to twelve months or more. In situations where the eggs are removed from the aquarium immediately after spawning, the pair is capable of spawning every seven to ten days. Around the age of approximately three years, spawning frequency will decrease and eventually cease.

When the pair is ready to spawn, they will choose an appropriate medium upon which to lay the eggs and spend one to two days picking off detritus and algae from the surface. This medium may be a broad-leaf plant in the aquarium, a flat surface such as a piece of slate placed vertically in the aquarium, a length of pipe, or even the glass sides of the aquarium. The female will deposit a line of eggs on the spawning substrate, followed by the male who will fertilize the eggs. This process will repeat itself until there are a total of 100 to more than 1,200 eggs, depending on the size and health of the female fish. As both parents care for the offspring throughout development, the pair will take turns maintaining a high rate of water circulation around the eggs by swimming very close to the eggs and fanning the eggs with their pectoral fins. In a few days, the eggs hatch and the fry remain attached to the spawning substrate. During this period, the fry will not eat and will survive by consuming the remains of their yolk sacs. At one week, the fry will detach and become free-swimming. Successful parents will keep close watch on the eggs until they become free-swimming. At the free-swimming stage, the fry can be fed newly-hatched brine shrimp (Artemia spp.) or microworms. It is generally accepted that brine shrimp are the superior choice for fast growth rates of fry.

Compatibility with other fish

Typically in pet stores the Freshwater Angelfish is placed in the Semi-Aggressive category. But that proves false with some fish. For example, Platies (platy if singular), Tetras and Plecos (Plecostomus) all are compatible with Angelfish. Although, tetras will usually nip at their long fins.

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