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There are five Hawaiian amphidromous fishes (Gobiidae: Lentipes concolor, Awaous guamensis, Sicyopterus stimpsoni, Stenogobius hawaiiensis; Eleotridae: Eleotris sandwicensis). Amphidromous adults deposit eggs on the stream bottom. After hatching, larvae drift to the ocean for growth followed by postlarval migration back into the streams. Postlarvae were collected to construct a dichotomous identification key based on 12 morphological measures and ray counts from four fins. Overall, the presense of fused pelvic fins, standard length (SL), and fin ray numbers were the most useful in species separation. Gobies were separated from the eleotrid by the former having fused pelvic fins. Within the gobies, S. stimpsoni had the largest SL [mean (SD) = 20.5 (1.0) mm] with A. guamensis [15.8 (0.6)mm] smaller and L. concolor [13.7 (1.3) mm] and S. hawaiiensis [13.3 (1.0) mm] the smallest. Although SL alone could not separate L. concolor and S. hawaiiensis, the former had 5 first dorsal fin rays compared to 6 in all other gobies. Nineteen pectoral fin rays separated S. stimpsoni from A. guamensis, and SL along with anal and second dorsal fin ray number, separated A. guamensis from S. hawaiiensis. Canonical discriminate function analysis was used as an exploratory approach to confirm the dichotomous key. With all morphological features entered into the analysis, three significant discriminate functions were generated with the most highly correlated morphological variables within each function the same as those used in the dichotomous key. Additionally, regression models were generated for predicting SL from total length (TL) of three postlarval species. Measures of TL do not require excessive handling or killing specimens; however, SL is usually the preferred measure for body size. The ability to identify migrating postlarvae under a variety of conditions aids in data acquisition under circumstances where preservation may or may not be necessary for the research objectives.

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University of Guam



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