Age at recruitment of Hawaiian freshwater gobies

Synopsis Very little is known about the dynamics of native Hawaiian stream fishes. Five species are restricted, as adults, to freshwater streams and estuaries on the major islands of the Hawaiian archipelago. This paucity of information is partly due to difficulties inherent in determination of age and subsequent determinations of life history characteristics. In the present study, we determined the age of newly recruited Hawaiian gobies,Stenogobius genivittatus andAwaous stamineus using otolith microtechniques. Internal otolith increments were enumerated using scanning electron microscopy (SEM). Increments of newly recruited juveniles were deposited on a daily basis as validated through a marking study. Results showed recruitment at an average age of 135 and 161 days for these two species, respectively, with more rapid growth following recruitment to freshwater. Chemical analyses of otolith carbonate of the Hawaiian gobies by electron microprobe for strontium and calcium concentrations provided valuable insights into a fish's past history. A combination of structural and chemical analyses makes it possible to link growth and recruitment to nutritional and environmental factors. Such information developed as a broad model would be applicable to the management of Hawaiian gobies and would greatly improve the quality of information available for these unique fish populations and other fish populations