Spotted Danio

Adults reach only 4 cm long. Females are somewhat larger than males but less sleek and less brightly coloured. The body is silvery, decorated by a characteristic horizontal stripe of blue and white (sometimes blue and yellow) running from head to tail. Below this stripe, blue spots are scattered across the body.

This fish comes from Southeast Asia, specifically central Myanmar. Its range undergoes significant seasonal change. From November to April, the climate is relatively cool and dry by tropical standards, causing partial drying of water bodies. Then from May to September comes heat and heavy rain, flooding large lowland areas. The fish prefers small rivers, streams and ponds with rich bankside vegetation, and can be found in ditches and rice fields during the rainy season.

This is a very peaceful and active fish, though quite shy by nature. Tank mates should be similar in size and temperament. Keep them in a school of at least 8–10 individuals; in a group they become much less timid. Moreover, male spotted danios display brighter colours in a school as they compete to attract females.

A school of these fish needs at least 60 litres. Use a rocky substrate of fine pebbles, small stones and a few smooth boulders. Provide hiding places such as driftwood, roots and branches. Plants are best placed along the sides and back. A standard setup includes a heater, air pump, filter and light. When choosing a filter, consult a specialist to find one that cleans water effectively without creating strong internal flow. The spotted danio tolerates strong currents poorly; in nature it prefers calm water. A tight-fitting lid is essential, as these fish can jump. The water should be slightly acidic with low dGH. The temperature range is broad enough that supplementary heating is usually not needed in warm months. Change part of the water weekly and regularly clean the substrate and glass.

These fish are not fussy eaters and readily take dry, frozen or live food. Remember that diet directly affects colour intensity. Combine different foods, such as supplementing flakes and granules with bloodworm or daphnia.

The spotted danio is an egg-scatterer: females scatter eggs among plants while males fertilize them. This species is less fertile than other danios; one pair may produce no more than 50 eggs per breeding season. Parental care is weak, so after spawning the fish may eat their eggs and fry. However, some individuals can form stable pairs lasting several seasons. For successful breeding, use a separate breeding tank to protect the offspring from adults. Keep the setup simple, focusing on the substrate: use fairly large particles such as small stones or decorative glass beads that do not fit snugly together, creating gaps. As eggs sink, most fall into these gaps and become inaccessible to adults. A similar effect can be achieved with fine mesh on the bottom. Another method is to use low-growing, fine-leaved plants or moss such as floating riccia or Java moss covering most of the substrate—any substrate type works in this case. Dense plant growth provides reliable shelter for eggs. A breeding tank is usually 15–20 litres, filled halfway. Use an air pump, heater and simple small sponge filter to avoid sucking in eggs or fry. Spawning occurs in dim light, so a light source is not needed at first. Trigger breeding by maintaining water near the upper limit of 24–25 °C with slightly acidic pH, and feeding live or frozen bloodworm, daphnia and brine shrimp daily. After a time females visibly round out while males brighten and actively court. Now prepare a separate tank filled with water from the main aquarium, then move several females and the brightest males there. To initiate spawning, add small amounts of cool water every few hours, gradually lowering the temperature to about 20 °C. If done toward evening, spawning usually finishes by morning. Spawning ends when females become slimmer. Return the fish to the main tank. Fry hatch in 24–36 hours and start swimming freely a day later. Feed them specialized microscopic food for aquarium fish fry.

Balanced nutrition and correct conditions are the best prevention of disease in freshwater fish. If signs of illness appear, such as colour or behaviour changes, first check water parameters and quality. If needed, bring all values to normal before treating.

When buying, choose active, mobile fish with clean fins and no visible damage or coating on the body. Avoid fish showing signs of emaciation, sunken bellies or unnatural behaviour such as constantly hanging at the surface or in a corner. Ideally buy a school of 8–10 individuals at once to reduce stress during adaptation, as in the shop these fish may look pale and timid due to lack of shelter and stressful conditions.