Bigger? Fatter? Or is faster growth better? Considerations on condition in larval and juvenile coral‐reef fish

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Abstract Analyses of condition data are conspicuous by their paucity in the extensive tropical reef‐fish literature. Researchers typically quantify abundance at settlement, with little regard for the demonstrably variable quality of newly settled fishes. Condition may be functionally classified by indices of growth (e.g. the RNA‐DNA index or peripheral growth increments of the otolith), starvation (e.g. height of midgut mucosal cells), storage (e.g. lipid content), or morphometry (e.g. dry weight/length’), all of which are variably correlated with each other. At present all indices are species‐, stage‐, technique‐ and therefore often investigation‐specific, as laboratory‐reared larvae for calibrating field‐collected condition indices are often specific to the rearing procedure. RNA indices are particularly appropriate for estimating larval condition. In pelagic juveniles, or in recently settled juveniles, the width of peripheral growth increments of the otolith estimates average growth rate in length or dry weight during the previous few days, which discerns increasing from decreasing condition. Increment width changes in otoliths are particularly responsive to starvation events, and are correlated with RNA indices. Growth indices have great potential for determining which individuals were growing faster, thereby reducing their pelagic duration, and thus increasing their survival potential. The recent debate regarding whether bigger larvae have better survival could be re‐addressed, by determining if larvae with faster growth indices have relatively enhanced survival.