.
Wakatobi National Park, Indonesia. The Banggai cardinalfish is a paternal
mouthbrooder. 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. 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. 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. 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. == In captivity ==