Sex Ratio dan Pemangsaan terhadap Rekrut pada Ikan Hias Banggai Cardinalfish (Pterapogon kauderni)
The Banggai cardinalfish (P. kauderni, Koumans, 1933) is endemic to the Banggai Archipelago in Central Sulawesi, Indonesia. A paternal mouthbrooder with direct development, Indonesia made a commitment to ensure the conservation of this species, listed as Endangered in the IUCN Red List, at the 14th Conference of the Parties to CITES in 2007. Data are still limited on several aspects of the reproductive biology of this endangered species. The research reported here aimed to elucidate two phenomena related to the reproductive capacity of P. kauderni. Firstly, sex ratio is an important parameter as the reproductive capacity of P. kauderni is heavily dependent on the availability of males to brood the eggs and larvae. Secondly, it was suspected that predation, including cannibalism, would be a significant factor in the reproductive success of wild P. kauderni. A total of 120 specimens with a standard length > 40 mm (30 specimens from each site) were captured at random from Kadongo in Palu Bay (introduced population) and 3 sites in the Banggai Archipelago (Matanga, Tinakin Laut and Monsongan). Sex was determined through dissection and observation of gonads in the laboratory. Sex Ratio (SR) data for each site were compared and a t-test used to determine whether or not the sex ratio was significantly different from 1. Operational sex ratio (OSR) at each site was estimated based on the numbers of adult specimens of each sex available for breeding (excluding brooding males and fish with spent or immature gonads). Predation of recruits was studied through observation of brooding males and recent recruits in the waters of Palu Bay and Bone Baru, Banggai Island and analysis of data from a survey of P. kauderni populations and ecosystems (2011-2012), and linked to observations made in captivity (2010). Observed SR was 1.8, male-biased and significantly different from 1 (P<0.01), but OSR was not significantly different from 1 (P>0.5). Cannibalism of recruits by adult P. kauderni was observed in the wild. There was a statistically significant negative relationship between the observed percentage of adult P. kauderni and recruits (17 sites), and we consider that cannibalism is an important determining factor in the population dynamics of this species. Predation of recruits was observed in the wild by fish from the Scorpaenidae, Cirrhitidae, Labridae and Serranidae Families. The distribution patterns and survival of recruits seemed to be linked to the staged release of recruits observed in captivity and we suspect that filial cannibalism of recruits at the time of their release rarely occurs in the wild. Protective microhabitat (especially sea anemones) plays an important role in P. kauderni reproductive success.