Hemigrammus erythrozonus, also known as the glowlight tetra, is a small tropical fish found in the wild in the Essequibo River, Guyana, South America. It is silver in colour and a bright iridescent orange to red stripe extends from the snout to the base of its tail. The front part of the dorsal fins are the same color as the stripe. Other fins are silver to transparent. The Glowlight tetra is a peaceful, shoaling fish. It is slightly larger than the neon tetra, and its peaceful disposition makes it an ideal, and popular, community tank fish. It should be kept with similar sized, non-aggressive species.
H. erythrozonus is a medium size tetra growing to 4 to 5 cm (1.6 to 2 inches), notably larger than both neon tetras and cardinal tetras. It has a life span of 2 to 4 years when kept in good conditions.
It is an omnivore and in the aquarium eats small live, frozen and dry foods and flake foods. The feeding of vegetable matter is suggested to vary the diet.
It is readily available and usually very inexpensive. In some areas, golden and albino varieties are sold.
Glo light, glo-light tetra, and glolight are alternative common names. Hemigrammus gracilis is an older scientific name. The Red-line rasbora ( Rasbora pauciperforata) of Malaysia and Indonesia has markings and coloring very similar to H. erythrozonus, but is a member of Family Cyprinidae rather than a close relative.
They are best seen in the aquarium if kept in subdued lighting with a dark substrate. The water should be soft to slightly hard. d°GH of 6° to 15°. Use a slightly acidic pH of 6.8 in the range 6.0 - 7.5. They prefer a temperature of 25 °C in the range of 22° - 28° °C (72° - 82 °F). The hardiness of this fish allows it to easily adapt to harder water, although soft water is essential for captive breeding.
Like all small tetras, H. erythrozonus are happiest, most active, and most aesthetically pleasing when in a shoal. A minimum aquarium length of 60 cm will make them more comfortable when swimming. They prefer a well planted tank for hiding, but with some open water for free swimming. They should be a group of at least four with eight or more to make them feel secure. They tend to swim in smaller groups when a potential predator is present and swim freely when comfortable. They are often bought by aquarium owners to play a 'second fiddle' role to the neon tetra. Although they generally shoal separately from neons and cardinal tetras, they will often shoal alongside the latter, making an arresting visual spectacle.
Like most tetras, females are larger and more fat bodied than the more slender male. It may be hard to tell male from female until the fish are fully mature and females fill with eggs.
H. erythrozonus breed similarly to most egg-scattering small fish. They have been bred in captivity with a moderate level of difficulty. Breeding tank set up: A small 40L all glass tank with soft water (hardness up to 8°dGH and carbonate hardness should not be higher that 2°dCH). Water temperature should be kept between 26° and 28 °C (78 F to 82 F) . Adding peat to the tank or filter will soften water and make it slightly acidic. The tank should have dim or no lighting. They spawn over fine-leaved plants. Java moss (Vesicularia dubyana) or Fontinalis are suggested but not mandatory, or a spawning mop made of woolen thread. 1 cm glass beads or a spawning grate will help at the bottom to protect eggs from being eaten by adults.
Parents conditioning: Feed the pair kept separately with a variety of live foods, frozen food or dry food for a few weeks. When the female is well rounded transfer the pair to the breeding tank in the late afternoon hours. The spawning will occur in the following morning or the next day, if no spawning behavior is shown after 3 days start over the conditioning of the pair.
Spawning behavior: The male will swim around in a quick manner locking his fins when near the female. During the spawning act both fish roll over, when the female is the upside down position she ejects the eggs while the male fertilises them. Usually 120-150 eggs are dropped in plants and on the bottom. When the pair is done, they will be grazing for the eggs, they should be then removed.
Raising the fry: The eggs are light sensitive, so the breeding tank should be as dark as possible. Some believe the light contributes greatly to the eggs succumbing to fungal infections, though this has more to do with cleanness of tank and water conditions. The fry will hatch in 20 to 25 hours. They should look like small slivers of glass. Fry can be fed with infusoria, paramecium culture, crushed flakes, and rotifers after they have used all the yolk sack. By the 4th day should be introduced very small portion of newly hatched brine shrimp. The young consume relatively large pieces of live food such as nauplii of brine shrimp. Later microworms can be added to the diet.
Care of the breeding tank: Bottom sediment should always be removed and regular water changes done during the rearing period in order to avoid an accumulation of ammonium and nitrates which can be toxic to the fry. Although large quantities of fry will incubate in waters of low hardness, most of the fry may soon contract non-infectious, constitutional dropsy, and die within a short time. Those who survive will grow well. By the 12th day, they will show signs of a silver coloring. At three weeks of age, the fry will start showing their characteristic orange line and will be a size of about 1 cm. By two months they will be about 2 cm.