Diamond Tail Cory (Gastrodermus hastatus)

Common Name

Tail-spot Pygmy Cory, Hastatus Cory

Origin and Habitat

Gastrodermus hastatus occurs in South America across parts of the Amazon and Paraguay river basins, with records from Brazil, Bolivia, Paraguay, and northeastern Argentina. In the wild it favors very shallow marginal creeks, vegetated swamps, backwaters, and floodplain ponds where fine sand or mud is covered by grasses, leaf litter, and submerged stems. Water may be clear to tea stained with gentle flow and abundant micro life among plants. Large groups often form in midwater over plant beds rather than hugging the bottom.

Temperature and Water Conditions

Preferred temperature is 22 to 26°C, which is 72 to 79°F. Wild sites are typically soft to moderately hard and near neutral, with reported pH from about 6.0 to 7.5. In the aquarium, stability matters most. We do not recommend chasing numbers or altering chemistry except for special breeding projects. Keep oxygen high, current gentle, and nitrogen waste very low.

Appearance and Size

A tiny silver cory with a thin dark lateral line and the namesake black spearhead spot at the base of the tail, bordered by pale crescents. Females grow deeper bodied and a little larger, while males remain slimmer. Adults commonly reach about 2.5 to 3.0 cm, which is 1.0 to 1.2 inches, with exceptional individuals reported a bit larger.

Diet in the Wild

Tail-spot Pygmies pick at micro prey in and above plant beds. Their natural food includes tiny crustaceans such as cladocerans and copepods, insect larvae, and other zooplankton along with fine detritus sifted from surfaces and the water column.

Feeding in Captivity

Offer very small sinking foods and frequent micro live or frozen items. Crushed high quality flakes, micro pellets, and fine granules cover the staple. Supplement with baby brine shrimp, cyclops, daphnia, microworms, and finely chopped bloodworms. Feed in several small portions so food reaches midwater and the substrate without spoiling.

Behavior and Tank Setup

This species is peaceful and strongly shoaling, and it spends much of its time cruising midwater in a tight group. Keep a large school for confidence and natural behavior. A footprint oriented aquarium with open swimming space, fine sand to protect barbels, and dense stems, mosses, or floating plants for cover suits them well. Use gentle filtration with abundant oxygen. Ideal tank mates are small, calm fish such as ember tetras, tiny rasboras, ricefish, and other peaceful nano species.

Breeding

Gastrodermus hastatus follows the classic cory breeding pattern. Well conditioned fish spawn after cool, clean water changes and rich micro foods. During the T position the female holds a few eggs between her pelvic fins while the male fertilizes them. She then places the adhesive eggs on glass, fine leaves, or spawning mops in small batches over several hours. Adults will eat eggs, so either move the group after spawning or collect eggs from leaves and mops. At typical tropical temperatures the eggs hatch in several days. Start fry on infusoria or commercial liquid fry foods, then transition to newly hatched baby brine shrimp and microworms as they grow. Dense plants, moss clumps, and fine leaf structures help hide eggs and give fry safe foraging surfaces.

Quick Facts

• Scientific name: Gastrodermus hastatus
• Origin: Amazon and Paraguay river basins in South America
• Size: About 2.5 to 3.0 cm, which is 1.0 to 1.2 inches
• Temperature: 22 to 26°C, which is 72 to 79°F
• pH: Commonly 6.0 to 7.5 in the wild, stability is more important than exact value
• Temperament: Peaceful, highly shoaling, often midwater
• Diet: Micropredator of zooplankton and tiny benthic invertebrates
• Breeding: Adhesive egg layer, T position spawning on leaves, glass, or mops

Tropical Fish Co. Notes

Tail-spot Pygmies are different from many Corys because they spend so much time schooling in midwater, which adds lively movement to a planted nano tank. Keep a generous group, give them fine sand, and think small with foods. If you want to breed them, rotate spawning mops or broad leaves, collect eggs after lights out, and hatch them in a separate container with gentle aeration. With clean, stable water and steady micro feeding, a thriving colony will reward you with constant, captivating activity.