Life History Characteristics of a Small Cardinalfish, Ostorhinchus rubrimacula (Percoidei: Apogonidae), from Koro, Fiji

We describe aspects of the life history of the small cardinalfish Ostorhinchus rubrimacula from a single, large collection taken at Koro, Fiji. We determined size at maturity and batch fecundity, examined otolith microstructure to construct a vonBertalanffy growth curve, described a length-weight relationship, and performed a dietary analysis. Ostorhinchus rubrimacula is a gonochore that matures at 35 mm standard length (SL). Batch fecundity is related to body size by the equation: eggs spawned 1⁄4 0.0013(SL). Assuming each otolith ring corresponds to 1 day in age, the oldest individual in our collection lived 274 days. Growth is described by the equation: SL 1⁄4 40.84[l e 0:014ðage in days 22:45Þ]. Total body mass (mg) 1⁄4 4.806 10 (SL). Ostorhinchus rubrimacula feeds primarily on harpacticoid copepods, but isopods (mostly gnathidean) and polychaetes were also important dietary components. Perhaps because they are usually unimportant in food or aquarium fisheries, the life histories of small, cryptic reef fishes are largely unknown. However this is often the most abundant and speciose group of fishes found on coral reefs. As reef-fish ecologists attempt to generalize about factors that structure reef-fish communities, it becomes increasingly important to understand the life history characteristics of all members of the coral-reef fish community. The high numerical abundances, small body sizes, small home ranges, and presumptive short life spans make small cryptic fishes ideal candidates for field experiments evaluating the importance of ecological processes by examining their effects on population demography. The first step in any such study requires a description of basic demographic parameters of the model species. The family Apogonidae (cardinalfishes) contains over 200 species from 22 genera (Nelson 1994). Apogonids typically rank second or third of all reef fish families in abundance and species diversity (Bellwood 1996). Most cardinalfishes feed on invertebrates found on coral reefs or open sand during the night (Chave 1978) and repeatedly return to the same shelter site on the reef during the day (Marnane 2000), usually in multispecific aggregations in caves or branching corals (Greenfield and Johnson 1990). Thus these fishes may influence trophic pathways by concentrating energy and nutrients, in the form of fish biomass and waste products, to predictable locations on coral reefs (Marnane 2000). We describe the reproductive patterns, age and growth, and diet of a population of a Pacific Science (2006), vol. 60, no. 2:225–233 : 2006 by University of Hawai‘i Press All rights reserved 1 This paper is funded in part by a grant/cooperative agreement from the National Oceanic and Atmospheric Administration, Project No. R/FM-8, which is sponsored by the University of Hawai‘i Sea Grant College Program, SOEST, under Institutional Grant No. NA16RG2254 from NOAA Office of Sea Grant, Department of Commerce. The views expressed herein are those of the authors and do not necessarily reflect the views of NOAA or any of its subagencies. UNIHI-SEAGRANT-JC03-09. This work was also supported by NSF (DEB 0102745 to D. W. Greenfield and J. E. Randall) and NIH (RR03061 to the University of Hawai‘i Biological Electron Microscope Facility). This is contribution 2005-009 of the Pacific Biological Survey and Hawaii Institute of Marine Biology contribution No. 1202. Manuscript accepted 2 June 2005. 2 Hawai‘i Institute of Marine Biology, P.O. Box 1346, Kāne‘ohe, Hawai‘i 96744 and Department of Zoology, University of Hawai‘i, 2538 The Mall, Honolulu, Hawai‘i 96822. 3 Current address: Bishop Museum, 1525 Bernice Street, Honolulu, Hawai‘i 96817 (e-mail: klongenecker@