An evaluation of sexual macroscopic staging applied to Gulf of Mexico fishes
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An evaluation of sexual macroscopic staging applied to Gulf of Mexico fishes

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    "During 2011, a congressionally supplemented fisheries survey was conducted in the northern Gulf of Mexico (using 6 vessels) from April to October. All fish captured on hook-and-line gear were macroscopically sexed and staged for reproductive condition. Gonads were dissected and histologically examined for a subset of randomly selected fish, as well as all female red snapper (Lutjanus campechanus). To obtain further detail on a hermaphroditic species, macroscopic and histological data on red grouper (Epinephelus morio) were extracted from NOAA archives. During the survey, most gonochorists (9 species) were sexed correctly (97%) in contrast to hermaphrodites (7 species, 68% correct). The red grouper data set, which afforded a larger sample size from more experienced readers also indicated some error in assigning 'field' sex to a hermaphrodite in that 81% (n = 2,153) were sexed correctly. Almost all errors were due to misidentifying males as females. Rarely were histological females misidentified. This result may occur because testes of protogynous fish retain the ovarian form. Macroscopic classification of reproductive stage (males and females) ranged from 55-68% correct in gonochorists and 53-55% for protogynous hermaphrodites. Although spawning females were often classified correctly more errors were associated with inactive, spent and maturing stages. These findings may reflect the difficulty in discerning early development and atresia of oocytes with the naked eye. Spawning males, especially hermaphrodites, were often misclassified as maturing which may indicate that the histological readiness to spawn may not always equate with 'running ripe' condition (extruded milt) in the field. Additional training may help reduce error in macroscopic staging. However, we believe these results indicate a need for routine collection and fixation of reproductive tissues by on-board observers which will enable histological assessment of spawning condition (fraction etc.) and sex ratio of our most economically important stocks."
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