Banggai Cardinalfish

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 [https://www.youtube.com/watch?v=eEUYPFm_Pzs& (Banggai cardinal fish, Secret Bay, Bali)]

The Banggai cardinalfish is the only member of its family that is diurnal. It is a demersal tropical marine fish that forms stable groups of about 9 individuals in shallow water, being most common at 1.5 to 2.5 m in depth. It inhabits a variety of shallow habitats, including coral reefs, seagrass beds, and open areas of sand and rubble. It is most common in calm habitats on the protected side of larger islands.

hosting juvenile Banggai cardinalfish, at the Vancouver Aquarium.]] It is often found associated with the seagrass Enhalus acoroides and the long spined sea urchin Diadema setosum. They are capable of hiding among the spines of sea urchins without being stung.

. Wakatobi National Park, Indonesia.]] The Banggai cardinalfish is a paternal mouthbrooder. The female plays an active role in courtship and pair formation, which occurs a few hours to a few days before spawning. Mating pairs establish spawning territories several meters away from the main group and vigorously defend them. The eggs are about 2.5 mm in diameter. The young remain in the male's mouth cavity for an undetermined period after hatching. Unlike many other species of marine fish, the Banggai cardinalfish lacks a planktonic stage in its life history. The species has a short lifespan, reaching around 4 years in optimal conditions in captivity, and perhaps 1 to 2 years in the wild.

Banggai cardinalfish are sexually monomorphic. The pairs form up to 2 weeks prior to spawning. The female courts the male from pair formation until spawning. The female's size determines the fecundity and egg size, but the male's size determines the reproductive output, or the number of the eggs that the pair produces. Therefore, pairing tends to occur among individuals of similar sizes, so the male is able to care for all the eggs that the female produces.

In Banggai cardinalfish, courtship behavior is usually initiated by the female. Upon choosing a mate, the female isolates her potential mate from other individuals in the colony by creating a spherical spawning site that is about 50–60 cm in diameter. The general movement that the female exhibits is called'side by side trembling' which is when the female approaches the male from behind with a vigorous trembling motion while the male stays motionless. Then she places herself alongside him and tilts her body thirty degrees outward from its vertical plane, when the male and female's caudal and anal fins come into contact. The female repeats this movement until the male responds with sporadic 'mouth opening,' a sign of receptiveness. Such courtship behavior may last from several hours to 2–33 days. When an intruder interrupts a female's courtship behavior, the female would rapidly and aggressively chase the intruder away if the intruder is of the same sex. However, when the secondary male, or the intruder male approaches, he, instead of the female, exhibits trembling behavior, and also helps to defend the female and primary male's isolated territory. If the primary male does not respond to female's trembling, the female leaves periodically to visit the secondary male and displays trembling behavior which often results in mating.

Although the females initiate courtship, female and male cardinalfish are mutually selective. Females have been observed courting larger males more intensively. Females have also been observed producing larger eggs for larger, hence more 'attractive,' males. Females are also able to increase egg size even after the onset of egg maturation if they encounter a new, larger male to brood its eggs. The 'side by side trembling' described in the previous section can be subcategorized into two different movements: 'rush' and 'twitch'. 'Rush' refers to the first part of the movement when the females approaches the male, folding her pelvic, dorsal, and anal fins together and quickly swimming past the male for a distance of 10–40 cm. Then she performs the 'twitch' by twitching or trembling her body close to the male. The intensity of the 'rush' behavior is important for the male in predicting the female's potential reproductive effort, as the intensity of the behavior correlates positively with clutch weight. However, the number of twitches performed per day strongly associates with how close to spawning the female is. By forming a pair with a female with more mature eggs, or closer to spawning, a male can increase his reproductive rate. Furthermore, he can match his readiness to spawn to females' by observing her 'twitch' behavior.

When the male accepts female courting, the female expels eggs from her urogenital papilla. Female Banggai cardinalfish produce a relatively small clutch, consisting of no more than 90 eggs that are 2–3 mm in diameter. Once about three-fourths of the egg mass protrudes from the female, the male takes the eggs from her. This process is immediate, taking no more than 2 seconds. Eggs may be lost in the process if the male drops them, as they are usually immediately consumed by other fish in the area. Males also have the ability to detect dead eggs and expel them from their mouths. The male broods the eggs in his mouth up to 30 days, during which he does not feed. After spawning, the female stays with the brooding male for at least a few days. Females aggressively defend their territory by immediately chasing any intruders that approach the brooding males. They also exhibit a relaxed form of 'side-by-side trembling', and confine the males to a small space.

Juvenile Banggai cardinalfish do not go through any pelagic larval phase. Instead, they experience a high growth rate. Although the free embryos maintain their size difference after hatching, they increase several times in weight while being brooded inside their father's mouth. Therefore, at release, juveniles are many times heavier than they were at hatching. Juveniles settle directly within the parents' habitat upon release from their father's mouth.

aquarium]] The Banggai cardinalfish is a popular aquarium fish among fishkeepers. The fish is collected by local fishers and sold into the aquarium trade. This species first appeared in the international trade around 1995 or 1996. By 2001, 600,000 to 700,000 fish were exported annually. Trade estimates for 2001 through 2004 are 700,000 to 900,000 fish per year with collection occurring throughout the archipelago. Surveys identified significant (>90%) declines in two populations that were fished from 2001 to 2004, including the extinction of a population off of Limbo Island.