Order Synbranchiformes
Suborder Mastacembeloidei
Fishes of this suborder have an eel-like body shape, but the presence of spines in the fins, skeletal structure, and other features indicate that they belong to the perciforms. Mastacembeloids are distributed in the fresh waters of tropical Africa and Southeast Asia.
Family Mastacembelidae
Representatives of this family (about 50 species) inhabit fresh and brackish waters of Tropical Africa, India, Southeast Asia, the Malay Archipelago, and China, where the northern limit of their range reaches Beijing. Several African species are endemic to lakes Tanganyika and Victoria. Spiny eels mostly inhabit calm backwaters of rivers and lakes with muddy or sandy bottoms densely overgrown with aquatic vegetation. These are typically nocturnal fishes; during the day they hide in thickets under driftwood and stones or burrow into the substrate.
Many species burrow completely, leaving only their eyes and the snout—crowned with sensitive nostril tubes—exposed. At the same time, the fishes remain on guard all the time, constantly moving their snout, which acts as an olfactory locator, and observing everything happening around them. At dusk, they go out hunting, feeding mainly on benthic organisms, and do not disdain planktonic forms either; larger species eat fish larvae and fry, as well as small crabs. They can travel out of water for about an hour.
Fishes of this family are characterized by a long, eel-like body with fine scales and reduced pelvic fins, a closed swim bladder, and an elongated snout ending in a mobile proboscis with olfactory pits. Spiny eels are characterized by the fact that their dorsal and anal fins merge with the caudal fin (if present) or with each other. In macrognathus, the unpaired fins are separated, while in mastacembelus they usually merge with each other. Males are smaller and more slender.
Spiny eels can be kept in a community aquarium, though they feel more at ease in darkened species tanks. All are predatory and should be kept with large fishes so they cannot be eaten. They are nocturnal. Most of them are very territorial. The aquarium should have plenty of hiding places and shelters consisting of caves, plants, and driftwood. Despite the fact that spiny eels are primarily bottom-dwelling fish, the aquarium with them must be tightly covered with glass. At night and in stressful situations, they are able to find the smallest opening (especially in the corners of the aquarium) to escape outside.
They do not have high demands on water quality, nevertheless, it should always be transparent and chemically as little polluted as possible. It is important to constantly monitor the oxygen regime; water aeration must be continuous. The main thing is that the body of water should not be cramped (the larger the bottom area, the better). They spend most of their time at the bottom, often completely burying themselves in the substrate, where they look for food.
They need a soft substrate made of fine sand, preferably without silt. Therefore, regular cleaning of the substrate is recommended. Without soil baths and in old water, the fish’s normal mucus secretion is disrupted, their skin becomes covered with ulcers, acquiring a bluish marbled appearance that turns into ulcers and a moss-like coating, with mucus falling off in flakes.
In case of fish diseases, the salinity of the water should be gradually increased (up to 10%) with a simultaneous increase in temperature (up to 32°C); frequent water changes and complex therapy with erythracycline (25-50 mg/l) and griseofulvin (10 mg/l) in the early stages ensure complete recovery of affected individuals. These bottom-dwelling fish feed mainly on worms. Food should be strictly live; larger species can eat fish larvae and fry. Part of the food should be given before turning off the lights.
They mature in the second year of life. Females ready for spawning have a large belly, with a mass of eggs clearly visible through the body wall. Macrognathus spawn in plant thickets, while mastacembelus spawn by crawling along the bottom and gathering in balls inside ceramic and plastic tubes. pH 7.0-8.0; dH 6-15°; T 22-28°C.
Macrognathus aculeatus, circumcinctus, pancalus, siamensis.
Syngnathus abaster, spicifer, typhle. 
