Yellow Finned Hillstream Loach – (Gastromyzon Viriosus)



Gastromyzon Viriosus is also known as “Yellow Finned Hillstream Loach” or “Striped Borneo Sucker” is a member of the Gastromyzontidae family. Tatau River in Malaysia’s Sarawak region is the natural habitat of this fish.

Gastromyzon Viriosus is an endemic species which belongs to Malaysia. The name consists of the combination of the Greek words “gaster (stomach) ” and “myzo (to suckle)” and the Latin word “viriosus (strong).”
Gastromyzon Viriosus lives in the hills of Borneo, approximately 1350 meters above sea level, in shallow oxygen-rich waters. When suitable conditions are provided, they can live up to 3-4 years.



Gastromyzon Viriosus can grow up to approximately 5.5 cm in length. The dominant color on the skin of the fish is dark brown. Besides, it has 8-10 cream-colored lines. The tail and upper fin are yellow and include black rounded and striped patterns. In stressful environments, skin colors may fade, and spots may become invisible. The most distinctive feature of the fish is its body structure that narrows from the head to the tail. Adult females are slightly larger than adult males.

Behavior and Compatibility

Gastromyzon Viriosus is quite peaceful and can live in harmony with suitable tank mates. However, it is known that they have problems with species that are larger, aggressive, or have regional ownership. When environments similar to their natural life are created and kept in groups, they will display an even more calm attitude. Therefore, it is recommended to create groups of 4 or more fish in the same tank. On the other hand, in some cases, it has been reported that some individuals display regional protection behaviors, especially at feeding points. But, these behaviors are not causing any serious fights and injuries to the fish.

Water Parameters

Temperature: 20-24 ° C
pH: 6,5 – 7,5
Hardness: 1-12 dGH

Gastromyzon Viriosus can live in warmer waters as long as the dissolved oxygen level in the water is maintained. Fading in the colors of the fish is a sign that the water temperature is higher than necessary. It also likes higher water flows while compared to other fish.

Proper Tank Conditions

If only one fish is to be raised, 30 liters, if a group is grown, 80 liters and above aquariums are sufficient. The most important point in the healthy growth of this fish is the oxygen level in the water. Gastromyzon Viriosus requires clean and oxygen-saturated waters. For this reason, it is necessary to use a slightly stronger filter with a high filter media capacity. Make sure that the filter system is doing 10-15 turnovers per hour. Replacing 25 percent of the water in the aquarium weekly is also critical to maintaining the water quality.

Gravel, sand, rocks, or mixtures of these can are proper to use as the substrate in the aquarium. This fish lives in high current waters in its natural environment. Therefore, creating a high flow water environment is best to comfort for fish. The point that should not be forgotten most aquarium plants are not good with high flow water. Therefore, plants such as Java Fern and Anubias can be placed as decorations in the aquarium to create a natural habitat. Another advantage of using plants is that they increase the amount of oxygen in the water that the fish need.

One of the usual behaviors of this fish is to climb the aquarium glass. For this reason, it is significant to take precautions by covering the aquarium top. Lighting is not critical for this fish, but high-intensity light can be used to maintain the healthy growth of plants and algae in the aquarium.

Gastromyzon Viriosus make good tank mates with smaller, calm, and peaceful aquarium creatures. Danios, Barbs, Gobies, Swordtails, freshwater snails, nerite snails, and black devil snails are some that can live in harmony with this species. If keeping with dwarf shrimps is planned in the aquarium, it should be remembered that Gastromyzon Viriosus may accidentally eat the shrimp fry. They should not be in the same environment with crayfish and freshwater crabs since they can catch and kill them.

What should be noted is that the death ratios are very high in newly established tanks due to the unavailability of the food sources such as algae and biofilm. They must be kept in well-established and cycled tanks.


Feeding these fish can be problematic. In newly established tanks, if they cannot find enough food, they will eventually die. If a long-term and healthier diet is planned, the best solution is growing algae in the aquarium. The aquarium must be well established and cycled with algae growth maintained over the surfaces before adding this fish for best. Also, algae can be grown in a different container and fed as a nutrient to the main tank. Some veggies such as spinach, cucumber, or zucchini and frozen bloodworms, algae wafers, or high-quality dry foods are also ideal for feeding this fish. The most significant point on that is to deliver the food to the tank bottom for the fish to reach it. In case of many surface swimming fish exist in the aquarium, they will eat all the food before sinking to the bottom. While keeping this fish in a community tank, keepers must consider the feeding accordingly.


Unfortunately, there is not very clear information about the breeding of this fish. The closest information comes from an article written by the German aquarist Philipp Dickmann in 2011. This article includes G. scitulus and G. monticola, which are the same family species.


He put a pair of G. scitulus in a 30 liters tank with no filter and substrate but high aeration. Various plants were used as decoration material. He applied a rich diet of live foods and frozen mosquito larvae before breeding occurs. Along with the rich diet, the water temperature was maintained at 28°C for a period of 8 weeks and 32°C for 2-3 weeks. After observing courtship behaviors in these parameters, the temperature was lowered to the standard level of 25°C, and as a result, fish spawned at that lower water temperature. When it was seen that approximately 100 tiny eggs were released, parent fishes were removed from the breeding tank. After 3 days, the eggs hatch and the fry started to emerge. But, all the fry died within 3 weeks due to low water quality.

According to the latest experiences and information about this fish family, the spawning occurs in well-aerated tanks with well-conditioned pairs. The fish spawns in the water column, and the water flow washes away the eggs. Later the eggs drop to the gaps in the gravel or the pebbles and hatch there. The fry is tiny and very sensitive to water quality, even minimal pollution. The survival of the juvenile depends entirely on the water parameters and biofilm growth in the tank. On the other hand, Gastromyzon Viriosus does not exhibit parental behavior, and the fry grows alone by feeding on the biofilm and algae.

In conclusion, this fish has peaceful behavior and is preferred by aquarists in most community tanks. They should be raised in groups of 4-6 individuals to show social behavior. Some special parameters that are necessary for a healthy life make them difficult to maintain. For this reason, it is not suitable for beginner aquarists. The specialist knowledge of reproduction is not sufficient, and successful breeding experiences are limited.

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