**Rasbora sarawakensis**, commonly known as the Sarawak Rasbora or Sarawak Scissortail Rasbora, is a beautiful, small, and peaceful freshwater fish species belonging to the family Cyprinidae. It originates from the rivers and streams of Sarawak, Malaysia, and nearby regions of Borneo. While it is not as widely known as some other Rasbora species, it is highly appreciated by aquarists for its graceful swimming and attractive coloration.

### Appearance
Rasbora sarawakensis has a slender, elongated body that tapers towards the tail, giving it a streamlined appearance. The fish is generally silver to gold in color with a subtle iridescence that reflects light beautifully. A distinctive black horizontal stripe runs along the length of its body from the nose to the tail, which adds to its elegance. The fins are often transparent or lightly tinted, and the forked tail, resembling a pair of scissors, gives it the nickname "Scissortail." This feature is especially prominent when the fish is swimming, as it makes quick, darting movements through the water.

### Size
Sarawak Rasboras are relatively small, typically growing to about 2 to 2.5 inches (5 to 6 cm) in length when fully mature. Their small size makes them ideal for community tanks and nano aquariums.

### Behavior and Temperament
Rasbora sarawakensis is a schooling fish that thrives in groups of six or more. These fish exhibit much more natural behavior when kept in groups, as they swim together in tight formations, creating a mesmerizing display of synchronized movement. They are peaceful and non-aggressive, making them excellent tank mates for a variety of other community fish. As mid-level swimmers, they spend most of their time darting through the water column, rarely interacting with the substrate.

In a well-planted tank with dimmer lighting, they tend to display their best colors and remain active, making them a great addition to a natural-looking freshwater aquarium.

### Habitat and Tank Requirements
In their natural habitat, Rasbora sarawakensis can be found in slow-moving rivers, streams, and forested swamps with clear water. To replicate their environment in captivity, here are some essential tank requirements:

1. **Tank Size**: A minimum of 15-20 gallons (55-75 liters) is recommended for a small group. Larger groups will benefit from more space.
2. **Substrate**: A dark, sandy substrate can help bring out their colors and create a more natural look. Fine gravel is also suitable.
3. **Water Parameters**:
- Temperature: 72-79°F (22-26°C)
- pH: 6.0-7.0
- Hardness: Soft to moderately soft water (2-10 dGH)
- They prefer well-oxygenated water with gentle currents.
4. **Decor**: Provide plenty of live plants such as Java fern, Anubias, and floating plants like duckweed to create shaded areas and offer a sense of security. Driftwood and rocks can also be used to simulate their natural environment.
5. **Lighting**: Moderate to low lighting will help them feel more comfortable, and their iridescence tends to show better under subdued lighting conditions.
6. **Filtration**: A gentle filtration system is ideal, as these fish are accustomed to calm waters. Overly strong currents can stress them.

### Diet
Rasbora sarawakensis is an omnivore with a preference for small, live or frozen foods. In the wild, they feed on small invertebrates, plankton, and plant matter. In captivity, they will readily accept high-quality micro pellets, flakes, and freeze-dried or frozen foods like daphnia, brine shrimp, and bloodworms. To maintain optimal health and coloration, it's best to provide them with a varied diet that includes both plant-based and protein-rich foods.

### Breeding
Breeding Rasbora sarawakensis in captivity is possible but requires some attention to water conditions and spawning behavior. Like many Rasboras, they are egg scatterers. To encourage breeding, raise the temperature slightly (around 77-80°F) and provide fine-leaved plants or spawning mops for the fish to lay their eggs on. The female will scatter eggs, and the male will fertilize them, but parents do not guard their eggs. In fact, it’s common for them to eat the eggs, so removing the adults after spawning is recommended.

The eggs typically hatch in 24-48 hours, and the fry can be fed infusoria or very fine commercial fry food initially, moving on to baby brine shrimp as they grow.

### Common Health Issues
Rasbora sarawakensis is generally a hardy species, but like all aquarium fish, they are sensitive to poor water quality. Maintaining a clean tank with regular water changes is essential to prevent stress and disease. They are particularly prone to bacterial infections and fin rot if kept in suboptimal conditions, so it’s important to monitor water parameters regularly.

### Tank Mates
Given their peaceful nature, Rasbora sarawakensis can be housed with a wide variety of other community fish species. Ideal tank mates include:
- Other small Rasboras (such as Harlequin Rasboras or Lambchop Rasboras)
- Tetras (Neon Tetras, Ember Tetras)
- Dwarf gouramis
- Small corydoras catfish
- Small peaceful loaches (such as Kuhli Loaches)

Avoid keeping them with large, aggressive, or fin-nipping species like barbs or cichlids, as Rasboras can easily be stressed or outcompeted.

### Summary
Rasbora sarawakensis is a delightful species for freshwater aquarium enthusiasts. Its elegant appearance, schooling behavior, and easy-care requirements make it an excellent choice for peaceful community tanks. When provided with the right environment, good water quality, and a balanced diet, these fish can live for several years, bringing constant beauty and activity to any aquarium setup.