Order Perciformes
Family Polycentridae
Freshwater fishes from South America. The body is massive, more or less compressed laterally, quite high in some species. As a rule, they have large heads, camouflaged body coloration, and a very large, wide, protrusible mouth. True predators of striking voracity. They are capable of catching quite large prey relative to their body size, including small fish, aquatic insects, and other invertebrates. They attack selected prey, which can be up to half the size of the predator’s body, with a sudden rush from hiding spots. Their appearance makes them interesting for aquarium maintenance.
Given the above, it is advisable to keep these fish in a species tank. Most species lead a solitary lifestyle, requiring dense plant thickets, numerous hiding spots made of rocks and flower pots, and dim, diffused lighting. The fish are sensitive to water purity and do not tolerate frequent water changes. Aeration, filtration, and water replacement are necessary. They mature at 10-20 months. They live for 3-5 years.
Genus Monocirrhus.
— Amazon Leaffish — Monocirrhus polyacanthus [Heckel, 1840]. Synonym: Monocirrhus mimophyllus. (Eng.: Amazon Leaffish, South American Leaf Fish). Amazon and Rio Negro basin, Guyana. 8 cm. These fish resemble a fallen, partially decomposed tree leaf. The body not only copies the color of a dead leaf but also its shape, right down to the tip of the leaf. The body is flat, olive-brown in color with coffee-colored smudges, dark spots, and transverse stripes vaguely resembling leaf veins. When viewed head-on, the heavily compressed laterally, slender body turns into a vertical line. It also has a “petiole” – an appendage on the lower lip. The shape and coloration of the fish allow it to successfully hide from enemies.
When frightened, it does not flee to the depths like other fish, but freezes with fins spread out and sinks to the bottom, spinning like a leaf. The resemblance to a leaf is further enhanced by the fact that the fish maintains an inclined, almost lying posture. Hiding among numerous real fallen leaves, this ambush predator almost completely merges with the background, which ensures its success in hunting potential prey.
Cautiously, slightly moving its dorsal and pectoral fins, it creeps up on a school of fish; even the gill cover on the side facing the prey does not move. Pectoral fins are hard to see, and both ends of the anal and dorsal fins are equally transparent, and it is through the high-speed flickering of these fins that the fish conducts its stealthy hunt. Then a huge tube-mouth, equal to a third of its body, extends, forcefully pulling water into the mouth, and the entire school is drawn in along with the water. Their body coloration can change like a chameleon: one day they are dark brown, another day golden, and the third day covered in spots. Males are brighter, larger than females, and the ends of their unpaired fins are pointed. During the spawning period, the male is orange-yellow.
Most of the day they hang motionless head-down among plants, resembling floating leaves. An ambush predator attacking small fish. To escape predators, when in danger, it is capable of playing “ opossum play” (feigning death): it folds its fins, freezes, and falls flat or somersaults to the bottom like an old leaf, remaining motionless for 30-40 minutes. They accept only live food (bloodworms, small fish). It is incredibly difficult to wean them off live food. Without feeder fish, they quickly perish.
They should be kept in a separate aquarium only with individuals of their own species and only if you have a large supply of small fish to feed them. The aquarium should be densely planted with both broad-leaved and fine-leaved plants, featuring driftwood. They are aggressive, quarrelsome (among themselves) fish. Young fish exhibit pronounced schooling behavior, which later fades. Upon reaching sexual maturity, the fish live solitary lives.
Only large fish are suitable as neighbors, while loricariids and relatively large Corydoras serve as bottom-dwelling companions. Prefers soft and acidic water. Quite sensitive to water quality and temperature. Aeration, water filtration, and weekly water changes in small portions are necessary. A slow water current is required. Failure to maintain necessary conditions results in loss of appetite and activity.
A danger signal is the darkening of coloration: during illness, extreme exhaustion, or drastic mismatch of conditions, it turns black with emerging whitish spots (it is important not to confuse this with normal uneven coloration), and the fish become sluggish and apathetic. Do not test the resilience of your pets; provide them with the most comfortable conditions possible. They mature in 12-16 months. They live up to 8 years. dH 2-10°; pH 5.5-6.5; T 23-26°C.
Identification: Amazon Leaffish — Monocirrhus polyacanthus.
Genus Polycentrus.
— Polycentrus schomburgki [Muller & Troshel, 1848]. Synonyms: Mesonauta surinamensis, Polycentrus tricolor. Guyana, Venezuela, Trinidad – coastal caves of slow-flowing rivers. 6 cm. The body of the fish is compressed laterally and almost disc-shaped. The head is very large. Large eyes and a wide slit-like mouth stand out on the head. The mouth is equipped with numerous teeth located on the jaws, pharyngeal bones, and palate. This fish got its common name due to the colorless caudal fin and the posterior part of the anal and dorsal fins, which makes the fish look clipped off.
The shape of the fins is interesting. The dorsal and anal fins are well developed and consist of two parts: the front part is long and arched, and the rear part is much higher, extending backward at an angle of about 45°. Pectoral fins are shaped like highly elongated triangles tapering at the end, usually directed vertically downwards. Pelvic fins are heavily elongated. Adult males are almost a third larger than females, slightly slenderer, have a larger forehead, and most importantly, completely different coloration. Their body is brownish-black, with small white-blue dots scattered randomly across it.
When excited, the overall color is coal-black; when calm, dark gray, sometimes gray-brown. Depending on the fish’s mood and lighting, the coloration easily changes from light brown to velvet-black. Four dark transverse stripes of the same color run obliquely across the body, with even darker dots located on them, vaguely resembling leaf veins. Three dark spots with a light border are located on the gill cover.
Along with the darkly colored body, their caudal fin and the rear parts of the dorsal and anal fins are completely transparent, making the fish appear clipped off. The transparent fragments of the unpaired fins of males darken with age. Females are modestly colored – against a gray-brown background, bands that appear and disappear depending on the fish’s mood and regular small black spots are visible. During spawning, the female becomes light. Young fish have a light yellowish-brown coloration with a golden sheen, with spots scattered all over the body and periodically disappearing oblique stripes.
This predatory, aggressive fish externally resembles an old, rotted leaf. Usually, fish stay alone, hiding somewhere under a leaf or in other shelters. When frightened, it does not flee to the depths like other fish, but freezes with fins spread out and sinks to the bottom, spinning like a leaf. The resemblance to a leaf is further enhanced by the fact that the fish maintains an inclined, almost lying posture. Ambush predators lying in wait for prey are active at twilight and night, and stay in hiding during the day. Cautiously, slightly moving its dorsal and pelvic fins, it glides through the water, and then suddenly forcefully pulls water along with prey into its mouth, which expands into a tube equal to a third of its body.
They behave aggressively towards representatives of both their own and other species; they can swallow a fish that has reached 1/3 of their own body size, so they can only be kept together with representatives of their own species or larger individuals of other species. Anything that does not move is not food for them. They do not like bright light, trying to retreat into the shade, under a sprawling plant bush, into a hiding place, or simply into a dark corner. They also dislike strong water movement.
The presence of hiding spots is mandatory; dead-end ones are preferred, where the internal diameter should allow the fish to turn around, and the minimum depth should be at least 3/4 of the body length. Sensitive to temperature fluctuations and water changes. Fish are fed bloodworms, tubifex, and small fish. They mature in 11-13 months. Spawning is paired in a flower pot or on the underside of a broad leaf. The male cares for the eggs. They live up to 6 years. T 22-26°C; dH 3-20°; pH 6-7.2.
Description of the family Scatophagidae, Selenotoca multifasciata.
Nandus nandus, Nandus nebulosus. 
