Sundasalanx

This fish is strikingly miniature, even tiny. Adults grow to only 2 cm in length. Sexual dimorphism is weakly expressed, and it is almost impossible to distinguish males from females externally. Sundasalanx has an elongated body and a very small head. Its main distinguishing feature is not so much its coloration as its absence, as the fish is almost completely transparent. Through the body, the skeleton and internal organs are clearly visible, gathered in a small, silvery “sac.”

Its natural habitat is the island of Borneo: the type locality lies in the Kapuas River basin, and the species is known from both the Indonesian and Malaysian parts of the island. These fish prefer murky waters with slow currents or stagnant water. During the day, they usually stay near the silty bottom, and at night and dusk, they may rise closer to the surface.

These peaceful schooling fish, however, due to their tiny size, have a very limited choice of aquarium mates. It is advisable to keep them separately from other fish species.

Thanks to their modest size, adult Sundasalanx fish can feel comfortable in nano-aquariums of about 20 liters. When decorating such an aquarium, it is recommended to use a soft sandy substrate, driftwood, and low-growing aquatic plants that can thrive in low light. It is important to provide an efficient filtration system to maintain high water quality, and to regularly clean the aquarium. When choosing a filter, opt for models that do not create excessive current and whose water intake openings are reliably protected to prevent accidental suction of the fish into the cleaning system. Weekly partial water changes (20–30% of the total volume) are also an essential procedure to prevent the accumulation of organic waste.

In natural conditions, the diet of these fish consists mainly of microorganisms such as invertebrates, crustaceans, and annelids. In a home aquarium, they should be offered similar products, for example, Artemia nauplii or Daphnia. It is also possible that they will accept specialized foods developed for fry.

Breeding has not been described. No sexual differences have been recorded for this species; in the related S. malleti and S. megalops males are told by a more intense dark marking on the lower lobe of the caudal fin. The species has essentially not appeared in the aquarium trade and seems to travel extremely badly.

No diseases that affect only this species have been described. Under suitable conditions — clean water, a balanced diet and calm tank mates — health problems usually do not arise. The most common cause of illness is a decline in conditions: it weakens the immune system, and the fish becomes vulnerable to infections that are always present in an aquarium. At the first signs of trouble — lethargy, wasting, refusal of food or clamped fins — check the basic water parameters and the levels of ammonia, nitrite and nitrate first. Restoring acceptable conditions often lets the fish recover on its own.

This species is extremely rare in retail and is practically not represented in the aquarium trade. When purchasing, it should be noted that the fish are very sensitive to transportation and keeping conditions, so it is extremely important to assess their general condition in the store. Healthy individuals should be active, exhibit schooling behavior, and show no visible damage or signs of emaciation. Due to their small size and specific dietary requirements, it is recommended to check with the seller in advance what the fish are fed and how they have been adapted to captivity.