A Comparison of Alternative Approaches to Discriminate Larvae of Striped Bass and White Perch

Abstract

Striped bass Morone saxatilis and white perch M. americana are sympatric in rivers and estuaries across a broad region of eastern North America. Discrimination of their larvae is often an important but problematic component of large ichthyoplankton monitoring programs: their larvae are morphologically similar (particularly at the post-yolk-sac stage) and often co-occur. In a blind test using hatchery-reared larvae of known species identity, we compared the traditional externally based approach (method 1) with three alternatives: an approach based on interdigitation patterns of osteological features of cleared and stained individuals that has shown high potential for post-yolk-sac larvae (method 2); an approach based on premaxillary and vomerine tooth counts (method 3); and a variation of method 2 designed as a key to shorten inspection time (method 4). Method 1 provided the highest overall correct identification rates for striped bass (98.5%) and white perch (96.8%). Internal osteological features (method 2) also offered greater than 90% correct accuracy in identifying larvae but only for post-yolk-sac larvae sufficiently developed to display unambiguous development of the characters. Neither method 3 nor 4 yielded acceptable correct classification rates. These results indicate that external morphology can provide high accuracy in discriminating striped bass and white perch larvae (although wild-caught larvae might display more confounding variation).