Background. The paternal mouthbrooding Banggai cardinalfish, Pterapogon kauderni Koumans 1933, has an exceptionally restricted endemic range for a marine fish, is traded internationally as a marine ornamental and listed as endangered in the IUCN Red List. This paper aims to contribute to the body of knowledge regarding the biology of this species, based on studies on the endemic population in the Banggai Archipelago and the introduced population in Palu Bay, Central Sulawesi Province, Indonesia. Materials and methods. Length frequency data collected over the period 2004–2012 (n = 23230) were analysed using the ELEFAN approach (FiSAT software). A length–weight relation was derived from measurements of 1002 individuals from the Banggai Archipelago. Specimens from the Palu Bay population were used to study reproductive parameters (n = 80), morphometric relations (n = 54) and feeding habits (n = 30). Results. The ELEFAN analysis suggested an annual recruitment peak (September to December) and VBGF parameter estimates of L∞ = 7.1 cm (SL), K = 0.74 year–1 and t0 = –0.11 year, suggesting first maturity at 1 year, and longevity of 3–5 years. Total mortality (Z) and natural mortality (M) estimates of 4.4 year–1 and 2.2 year–1 yielded fishing mortality F = 2.2 year–1 and exploitation rate E = 0.5. Length–weight relation parameters were: a = 0.18; b = 2.15. There was no significant morphological difference between sexes. Gonad maturation began at 2.9–3.5 cm SL, all specimens ≥ 4.2 cm SL were sexually mature. Mean observed fecundity (59, n = 21) and number of eggs brooded by males (59, n = 17) were similar. Observed sex ratio was 1.67 males per female. Gut content indicated an omnivorous, predominantly carnivorous diet. Copepods and decapod larvae were the most abundant components in adult (SL ≥ 4.2 cm) and sub-adult (SL ≤ 4.2 cm) diets respectively. Adult diet appeared to be more varied. No empty guts were observed. Conclusion. This study provides data for a major reassessment of Pterapogon kauderni life history parameters in FishBase, the global database of fishes. P. kauderni spawning is associated with the lunar cycle; the seasonal recruitment peak is probably related to improved reproductive success during the calm season. With strong indications of a decline in the endemic population due to habitat degradation and loss (independent of fishing pressure), current exploitation levels may be unsustainable. Research is required to further refine life-history parameters (e.g. sex ratio) and elucidate issues such as fasting in brooding male Banggai cardinalfish and ontogenetic differences in diet.

growth, mortality, length-frequency, ELEFAN, length–weight relation, maturity, reproduction, diet and feeding habits