Evaluation of Silver Carp Ages Derived from Seven Bony Structures in Midwestern U.S. Rivers

To our knowledge, there has not been a consensus on which bony structure should be used for aging the invasive silver carp Hypophthalmichthys molitrix.  Therefore, we analyzed the processing times and precision of seven different bony structures (commonly used for aging).  A total of 120 silver carp were collected from six different locations throughout the Midwestern U.S. (Illinois, Missouri, Mississippi, and Ohio rivers) via electrofishing.  Ages were evaluated for scales, vertebrae, opercles, pectoral fin rays, postcleithral bones, lapilli otoliths, and asterisci otoliths using methods provided by previous studies. Asteriscus otolith, opercle and scale annuli were difficult to discern and therefore not evaluated.  We found that pectoral fins rays, postcleithral bones, and lapilli otoliths, had similar processing and handling times; whereas, vertebrae processing was much more time intensive.  All structures with discernible annuli (pectoral fins rays, postcleithral bones, vertebrae, and lapilli otoliths) exhibited similar age assignments; however, lapilli otoliths provided more distinguishable annuli on older fish.  From this, we recommend use of lapilli otoliths for aging silver carp, because processing time was similar to other structures and yielded consistently older ages.  We recommend future efforts to validate the accuracy of lapilli otoliths.