Barcoding nemo: DNA-based identifications for the ornamental fish trade

Abstract

Background: Trade in ornamental fishes represents, by far, the largest route for the importation of exotic vertebrates. There is growing pressure to regulate this trade with the goal of ensuring that species are sustainably harvested and that their point of origin is accurately reported. One important element of such regulation involves easy access to specimen identifications, a task that is currently difficult for all but specialists because of the large number of species involved. The present study represents an important first step in making identifications more accessible by assembling a DNA barcode reference sequence library for nearly half of the ornamental fish species imported into North America.

Methodology/principal findings: Analysis of the cytochrome c oxidase subunit I (COI) gene from 391 species from 8 coral reef locations revealed that 98% of these species exhibit distinct barcode clusters, allowing their unambiguous identification. Most species showed little intra-specific variation (adjusted mean = 0.21%), but nine species included two or three lineages showing much more divergence (2.19-6.52%) and likely represent overlooked species complexes. By contrast, three genera contained a species pair or triad that lacked barcode divergence, cases that may reflect hybridization, young taxa or taxonomic over-splitting.

Conclusions/significance: Although incomplete, this barcode library already provides a new species identification tool for the ornamental fish industry, opening a realm of applications linked to collection practices, regulatory control and conservation.

Figure 1. Half-logarithmic dot plot of genetic distances within each species against genetic distances to nearest-neighbor.

For each species, there is a black dot showing intraspecific K2P distance and a red dot directly above or below it which shows the distance to its nearest neighbor. Sorting by intra- and interspecific distance allows the relative distances for each species to be seen. This graph indicates that few species have nearest-neighbor distances that are less than the mean intraspecific distance for that species. A line drawn at 1% separates most intraspecific from interspecific values.

Figure 2. Provisional splits of recognized species with intraspecific distances above 2.0% threshold species with groups associated with spatial differences.

(A) Pseudanthias squamipinnis, (B) Centropyge heraldi, (C) Chrysiptera cyanea and Chrysiptera starcki, (D) Valenciennea puellaris and Valenciennea wardii. Branch colors correspond to countries of specimen origin.