Abstract
Larval fish ecology is poorly characterized because sampling is difficult and tools for phenotypically identifying larvae are poorly developed. While DNA barcoding can help address the latter problem, ‘universal’ primers do not work for all fish species. The Roanoke River in the southeastern United States includes seven darters (Family Percide: Tribe Etheostomatini). We made 393 collections of larval fishes in 2015 and 2018, examined darter larvae for morphometric and pigmentation traits, developed PCR primers amplifying darter DNA, and evaluated three gear types for collecting larval darters. Amplified DNA sequences for 1351 larvae matched archived mitochondrial cytochrome oxidase I sequences for darters occurring in the ecosystem. Larval darters were classified to genus with 100% accuracy using the ratio of pectoral fin length to body length; however, identification to species using morphometrics alone was subject to a misclassification rate of 11.8%, which can be resolved by considering pigmentation patterns. Gear-types varied considerably in their capture efficacy for larval darters; most Percina larvae were collected in drift nets. Larval Percina species appeared in the drift before Etheostoma species in both study years. Application of molecular genetic and phenotypic tools to larval fish identification can advance understanding of larval darter ecology.
Highlights
Current knowledge of stream fish ecology—including such critical aspects as individual dispersal and habitat use—is based primarily on observations of post-larval stages
After visually screening all larvae and juveniles (< 10, barely past larval stage), we identified as larval darters or unknowns
While it would be useful to have real-time estimates of the phenology and species composition of emerging larvae, fisheries scientists have been limited in their ability to identify larval fishes—including darters—to species based on morphology and morphometrics
Summary
Current knowledge of stream fish ecology—including such critical aspects as individual dispersal and habitat use—is based primarily on observations of post-larval stages. While it has long been recognized that year-class strength and population dynamics are driven by larval survival in marine systems [1,2,3,4], relatively little is known in river and stream systems [5]. Spatiotemporal patterns of larval dispersal and habitat use in freshwater systems [6,7,8] are unexplored for most species, especially for species lacking economic importance. To relate abundance of larval fishes to population persistence and dynamics, we need a better understanding of the ecology of fish larvae. Studies of larval fish have been scarce due to the difficulty in collecting them effectively and identifying individuals to species [9].
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