(Sphaeramia nematoptera) is a popular and hardy aquarium fish that belongs to the Apogonidae family. They are also commonly known as the Threadfin Cardinalfish due to their long, delicate fins. These fish are native to the Indo-Pacific region, including the waters around Indonesia, the Philippines, and Malaysia.

In the wild, Onespot Cardinalfish are found in shallow reefs, lagoons, and other areas with clear, warm water. They typically grow to about 2 inches in length, making them a relatively small fish. Their body is elongated and slightly compressed with a pointed snout, while their fins are very long and delicate. They have a single black spot near the base of the tail, which is where they get their name.

The coloration of Onespot Cardinalfish is relatively uniform, with a silver-gray body and a black stripe that runs through their eye and down their back. They also have iridescent blue spots that shimmer in the light. Their fins are translucent, with long, threadlike extensions that give them an elegant appearance.

Onespot Cardinalfish are generally peaceful and can be kept in groups in aquariums that are at least 30 gallons in size. They are not picky eaters and will readily accept a variety of prepared and frozen foods, such as brine shrimp, bloodworms, and pellets. These fish prefer subdued lighting and plenty of hiding places, such as rocks, caves, and coral structures.

In terms of breeding, Onespot Cardinalfish are relatively easy to spawn in captivity. They are mouthbrooders, meaning that the female will carry the fertilized eggs in her mouth until they hatch. Breeding can be induced by slowly raising the water temperature and increasing the amount of light in the aquarium. Once the eggs are laid, they can be removed to a separate tank or left with the adults, who will protect them until they hatch.

Overall, Onespot Cardinalfish are a great addition to any community aquarium. They are hardy, peaceful, and relatively easy to care for, making them a good choice for both beginner and experienced aquarists. Their delicate fins and iridescent coloration also make them a visually stunning fish to observe.