FishMarineEasy
©AI Generated·Proprietary
Yellowstripe Cardinalfish
Ostorhinchus cyanosoma
An elegant marine reef fish characterized by a silvery body striped with bright orange or gold horizontal lines and glowing blue eyes. Ideal for small marine setups kept in closely-knit schools.
Water Temperature
22 - 28 °C
pH Value
8 - 8.5
Water type
Marine
Tank level
Bottom and middle
Adult size
8 cm
Minimum tank volume
>= 110 L
Minimum group
>= 5
GH
15 - 25 dGH
KH
8 - 12 dKH
Species description
Geographical Origin and Habitat: Apogon cyanosoma is native to the tropical Indo-Pacific, with a distribution range extending from the Red Sea and East African coast to the Great Barrier Reef, New Caledonia, and north to the Ryukyu Islands. It inhabits shallow coastal waters, sheltered lagoons, and outer reefs at depths of 1-15 meters, sheltering among the branches of Acropora corals or under rocky ledges.
Taxonomy and Morphology: Belonging to the family Apogonidae (cardinalfishes). It features a compressed, oval-shaped body with exceptionally large eyes and a wide, oblique mouth characteristic of nocturnal predators. The dorsal fins are completely separated. Adults reach a maximum length of 6-8 cm.
Social Behavior: Primarily nocturnal and highly gregarious. During the day, they form tight, stationary schools near corals or inside caves to evade predators, dispersing at night to feed on zooplankton in the water column. They have a peaceful, non-aggressive temperament towards other tankmates.
Coloration and Sexual Dimorphism: The body features a translucent silvery-blue base color marked by six distinct, bright orange-gold horizontal stripes. The eyes have a striking cobal-blue iris. There is no visible external sexual dimorphism; males are identified during spawning as they practice paternal mouthbrooding.
Care, breeding and tankmates
Aquarium Setup: Requires an established marine aquarium of at least 100 liters (approx. 25 gallons) to house a small group. Provide plenty of live rock arranged to create caves, shaded overhangs, and quiet areas away from bright light. Water current should be moderate, simulating protected reef lagoons.
Diet and Feeding: Carnivorous zooplanktivores. In the aquarium, they should be fed high-quality frozen foods such as mysis, brine shrimp, finely chopped krill, and fish eggs. They can be gradually transitioned to marine flake food or mini pellets. Feed twice daily, preferably under dimmed lighting.
Water Quality: Requires stable reef parameters: water temperature between 24°C and 28°C (75-82°F), salinity/specific gravity of 1.022 to 1.026, pH range of 8.1 to 8.4, and minimal nitrate and phosphate levels. Good water movement and efficient filtration (using a protein skimmer) are essential.
Compatibility and Cohabitation: Very peaceful, making them ideal for marine community tanks with quiet reef fish like clownfish, blennies, gobies, and small wrasses. Avoid keeping them with large, fast, or aggressive predators (such as lionfish or groupers) that could easily swallow them.
Aquarium Breeding: Known for paternal mouthbrooding. After spawning, the male collects the fertilized egg mass in his mouth and incubates them until hatching (7-10 days), during which he does not feed. Successful captive rearing is difficult and requires live rotifers.
Risks and Diseases: Susceptible to common marine parasites such as Cryptocaryon irritans (marine ich) and Oodinium ocellatum, especially when stressed by fluctuating water quality. Acclimatize slowly using the drip method, as they are sensitive to transport stress.
Geographic Origin and Distribution
Apogon cyanosoma is native to the tropical Indo-Pacific, with a distribution range extending from the Red Sea and East African coast to the Great Barrier Reef, New Caledonia, and north to the Ryukyu Islands. It inhabits shallow coastal waters, sheltered lagoons, and outer reefs at depths of 1-15 meters, sheltering among the branches of Acropora corals or under rocky ledges.
Origin
Tropical oceans and reefsCentral America and CaribbeanAfrica and MadagascarEast AsiaAustralia, New Guinea, and Oceania
Fish profile
- Temperament
- Territorial
- This species is peaceful, social, and largely nocturnal in nature. During the day, they exhibit a passive, hovering behavior, seeking shelter in caves or under ledges. While they are peaceful toward other fish, males may display minor territorial squabbles among themselves, especially in smaller tanks. They are ideal candidates for peaceful reef or community aquariums where they won't be intimidated by active swimmers.
- Diet
- Carnivore
- In their natural habitat, Yellow-striped Cardinalfish feed primarily on planktonic crustaceans and other small invertebrates. In a home aquarium, they should be offered a variety of meaty foods such as frozen Mysis shrimp, brine shrimp, and finely chopped krill. Over time, they may accept high-quality pellet or flake foods, though live and frozen foods remain preferred. Due to their large mouths relative to their body size, they should not be kept with very tiny ornamental shrimp.
- Life expectancy
- 3-5 years
- Under optimal aquarium care, the Yellow-striped Cardinalfish typically lives between 3 and 5 years. In the wild, their lifespan is considerably shorter, often around 1 year, due to intense predation and environmental factors. To maximize their longevity in captivity, it is crucial to provide a low-stress environment and maintain stable water parameters. A diverse, high-quality diet also plays a vital role in extending their lifespan.
- Adult size
- 8 cm
- The catalog's scalar value is 8 cm. The FishBase SPECIES table (v25.04 snapshot) source reports a maximum adult measurement of 8 cm for this species, recorded as total length (TL). The taxonomic record consulted is Ostorhinchus cyanosoma (v25.04); male or unsexed record. These figures are not interchangeable: the first is the profile's editorial reference, whereas the second is a published maximum under a specific measurement convention; differences among sources can reflect sex, population, life stage and measuring method.
- Sex ratio
- Group
- In the aquarium, Ostorhinchus cyanosoma can be kept in male-female pairs or small groups. If kept in a group, a social hierarchy will form, and they will generally exhibit peaceful behavior toward one another. Providing enough space and shelter is key to preventing territorial squabbles among conspecifics. A group of 5 to 6 individuals is ideal to observe their natural schooling behavior.
- Feeding frequency
- Twice daily
- Yellow-striped Cardinalfish should be fed small portions one to two times daily. Because they are naturally nocturnal, feeding them during the evening or with the aquarium lights dimmed can help encourage active feeding, particularly when they are newly introduced. Ensuring that food is distributed throughout the tank helps all individuals, including less dominant ones, receive adequate nutrition. Regular feeding helps maintain their energy levels and overall health.
- Bioload
- Low to Medium
- Yellow-striped Cardinalfish are small marine fish that reach a maximum size of about 8 cm. Consequently, their biological footprint is relatively low, making them suitable for smaller setups or community tanks. However, because they are sensitive to fluctuating water parameters, they still require reliable filtration and regular water maintenance. A well-established biological filter and moderate skimming are sufficient to keep the water clean and stable.
- Flow
- Moderate
- This species prefers low to moderate water flow in the aquarium. In the wild, they inhabit sheltered lagoons and reef areas, where they can hover without fighting strong currents. High water flow can cause stress and exhaustion, as they are not built for powerful swimming. Providing areas of calm water within the aquarium, such as behind rockwork or inside caves, is essential for their well-being.
- Jump risk
- No
- Reproduction
- Mouthbrooder
- Yellow-striped Cardinalfish are paternal mouthbrooders, exhibiting a fascinating reproductive behavior. During spawning, the female releases a mass of eggs, which the male fertilizes and then holds in his mouth. The male incubates the eggs for several days and does not feed during this entire period to protect the clutch. While they have been bred in captivity, rearing the tiny larvae requires specialized live foods like rotifers and a dedicated rearing tank.
- Compatibility & tankmates
- Peaceful
- Ostorhinchus cyanosoma is highly compatible with other peaceful reef-safe fish, such as firefish, small gobies, and peaceful wrasses. They should not be housed with large, aggressive predators like lionfish, groupers, or large wrasses that could easily view them as prey. Additionally, active and boisterous tankmates may intimidate them, keeping them hidden. They are reef-safe and will not harm corals, though they may consume very small ornamental shrimps.
- Tank level
- Middle/Bottom
- This species is typically found in the lower to middle zones of the aquarium. They prefer to hover in shaded areas, near caves, rocky overhangs, or branching corals. During the day, they will rarely venture near the surface, preferring the safety of sheltered spots. In a reef setup, they are often seen associating with the lower portions of the rockwork or near sea urchins.
Scientific Parameters & Models
FishBase
Window to the official scientific data of the species
Data synced on: 06/15/2026
- Trophic level
- 3.6 ± 0.56 se
- Resilience
- High (less than 15 months)
- Phylogenetic uniqueness (PD50)
- 0.5
- Bayesian Length-Weight
- a = 0.01349, b = 3.11
- VulnerabilityLow vulnerability (10 / 100)
Image gallery
Licensed images linked to the species or, when marked, to the closest representative taxon.
Related species
Recommendations grouped by close relatives, companion choices, and similar care.
