The Banggai Cardinalfish (Pterapogon kauderni) is a small tropical cardinalfish in the family Apogonidae. It is the only member of its genus. This attractive fish is popular in the aquarium trade. It is among the relatively few marine fish to have been bred regularly in captivity, but significant numbers are still captured in the wild and it is now an endangered species.
With its striking patterning and elegant, elongated fins, it is easy to understand why the Banggai cardinalfish has become extremely popular with the aquarium trade. The shiny, silvery body is distinctively marked with three vertical black bars, one running down the head and the other two down the fish’s flanks. Between the bars on the body, the Banggai cardinalfish is marked with white dots, which form a pattern unique to each individual. The front dorsal fin, is tasselled, and the second dorsal fin, anal fin and caudal fin are elongated. The fins all have black markings and, with the exception of the front dorsal fin, are also marked with white dots.
This species is restricted to the Banggai Islands of Indonesia. This species has an extremely limited geographic range (5,500 km²) and small total population size (estimated at 2.4 million). The Banggai cardinalfish is composed of isolated populations concentrated around the shallows of 17 large and 10 small islands within the Banggai Archipelago. A small population also occurs off Central Sulawesi, within Luwuk harbor. One additional population has become established in the Lembeh Strait (North Sulawesi), 400 km north of the natural area of the species distribution, following introduction by aquarium fish traders in 2000. Small populations seen (May 2014) in Secret Bay, north west Bali (Banggai cardinal fish, Secret Bay, Bali)
The Banggai cardinalfish occupies shallow coastal waters at depths between 1.5 to 5 metres, but is rarely found deeper than 2.5 m, and water temperatures ranging from 28 to 31 degrees Celsius. It generally prefers calmer waters, though some populations live in areas with strong surges and currents. Living near the seabed, this species is most commonly found around coral reefs, but also around seagrass beds and, less commonly, over small, open patches of rubble. Within these environments, it is normally found in association with various bottom-dwelling organisms, such as sea urchins, sea anemones, and branching corals.
The Banggai cardinalfish is remarkable among marine fishes for the extreme levels of genetic diversity found between its populations. Populations as little as five kilometres apart are as genetically distinct as separate species, a consequence of the Banggai cardinalfish’s highly limited dispersal capability, the strong currents and deep channels between the islands preventing interaction with populations at other sites.
Banggai cardinalfish live in small groups of usually between 1 and 6 individuals, though a group of 500 has been recorded. Reproduction in the Banggai cardinalfish begins with the female choosing a male; the pair then separate from the group and establish a territory, aggressively defending it from other fish that come too close. The female then initiates an unusual courtship ritual, swimming alongside the male, bodies touching, and making a trembling motion. This behaviour occurs repeatedly on both sides, with the only signs of the male’s receptivity being a darkening of the lower jaw and an occasional opening of the mouth. After several hours of this behaviour, the female spawns a mass of up to 75 large eggs (a very small number for a marine fish). These are quickly swallowed by the male, and brooded in a special pouch inside the mouth. The eggs take about 20 days to hatch, after which, the newly hatched embryos continue to develop in the male’s mouth pouch. After a further 10 days, when the young have reached around five to six millimetres in length, they are released. During the 30-day brooding period the male does not eat, and attends to the brood by frequently turning the eggs and expelling dead eggs and embryos. Once the brood are released, the male does not interact with them anymore. The small juveniles are most commonly found sheltering around sea anemones for protection. However, older juveniles and adults are more commonly found around branching corals and sea urchins.
The Banggai cardinalfish feeds principally upon tiny planktonic crustaceans, with copepods, in particular, making up about 80 percent of the diet. Nevertheless, this species is an opportunistic feeder, and will take a variety of small organisms from the water column and the seabed, including marine worms, molluscs and fish larvae. In addition, it plays an important role in its environment by preying on the larval stages of coral reef fishes’ parasites. The Banggai cardinalfish is preyed upon by various species, such as the crocodile-fish (Cymbacephalus beauforti), various lion-fish species (genus Pterois) and the grouper (Epinephelus merra). This species may live for two years in the wild.