Tropical Fish Hobbyist

The country of Burma (also known as Myanmar) has become one of the hotbeds of new aquarium fish discovery. Recent discoveries include the celestial pearl danio (previously known as the galaxy rasbora) Celestichthys margaritatus ROBERTS 2007 and the rose danio Danio roseus FANG & KOTTELAT 2000. This country has also produced many of the very small fish of interest to nano-tank hobbyists, including Microrasbora erythromicron ANNADALE 1918 and Indostomus paradoxus PRASHAD & MUKERJI 1929.

In the mid 1980s, a very small fish was described from the Irrawaddy (Ayeyarwady) River Basin, so small that it is considered to be one of the tiniest vertebrate organisms on the planet. This fish—Danionella translucida ROBERTS 1986—grows to just over a centimeter in length, and is less than a millimeter thick. There are currently two identified species in the genus Danionella, along with a few undescribed types. D. translucida is almost completely transparent (hence the common name micro glassfish) except for its eye and some distinctive black

spots on the lower half of its body. Those dots are so small, however, that seeing them without the aid of macro photography is difficult. The fish also lack scales, barbels, and a lateral line.

In the Wild and
in the Aquarium

D. translucida is found among the roots of floating plants and is a micro-predator that targets very small invertebrate organisms for food; about the largest food that an adult can handle is live Artemia nauplii. The water in their natural habitat is usually muddy, making these fish even harder to see. There is a hypothesis that the species produces a sound with a specific set of bones to help mates find one another in the turbid water. The water chemistry in the river is moderately soft at 100 to 200 ppm total dissolved solids, with a KH less than 3, and a neutral to slightly alkaline pH.

The species is not hard to accommodate in the aquarium—the only important thing is to avoid housing them with fish that might consider them an easy meal, which could be just about any other fish. Ideally, they

are best kept in a species-only tank. Water chemistry in the aquarium is not critical, so long as extremes are avoided. Very small tanks are appropriate, and a breeding group of 10 to 20 adults can be easily maintained in a 2½-gallon tank. Filtration should be gentle, so a small air-driven sponge filter will suffice. Power filters are a poor choice, since the fish can be sucked into the intake tube. A temperature between 72° and 80°F is acceptable.

Breeding

Breeding occurs daily. Females will produce three to eight relatively large eggs that can be seen in the abdomen as they develop. The addition of food equals eggs: a morning meal of baby brine shrimp or microworms, which are visible in the stomach of the fish, will create the day’s load of eggs that evening. They probably breed at night, because the females will be thin again by morning, waiting for another feeding to start making new eggs.