An accurate, comprehensive reference sequence library maximizes information gained from environmental DNA (eDNA) metabarcoding of marine fishes. Here, we used a regional checklist and early results from an ongoing eDNA time series to target mid-Atlantic U.S. coastal fishes lacking reference sequences. We obtained 60 specimens representing 31 species from NOAA trawl surveys and institutional collections, and analyzed 12S and COI barcode regions, the latter to confirm specimen identification. Combined with existing GenBank accessions, the enhanced 12S dataset covered most (74%) of 341 fishes on New Jersey State checklist including 95% of those categorized abundant or common. For eDNA time series, we collected water samples approximately twice monthly for 24 months at an ocean and a bay site in New Jersey. Metabarcoding was performed using separate 12S primer sets targeting bony and cartilaginous fishes. Bioinformatic analysis of Illumina MiSeq fastq files with the augmented library yielded exact matches for 90% of the 104 fish amplicon sequence variants generated from field samples. Newly obtained reference sequences revealed two southern U.S. species as relatively common warm season migrants: Gulf kingfish (Menticirrhus littoralis) and Brazilian cownose ray (Rhinoptera brasiliensis). A beach wrack specimen corroborated the local presence of Brazilian cownose ray. Our results highlight the value of strengthening reference libraries and demonstrate that eDNA can help detect range shifts including those of species overlooked by traditional surveys.

Here we describe GoFish, a strategy for single-species environmental DNA (eDNA) presence/absence assays using nested PCR. The assays amplify a mitochondrial 12S rDNA segment with vertebrate metabarcoding primers, followed by nested PCR with M13-tailed, species-specific primers. Sanger sequencing confirms positives detected by gel electrophoresis. We first obtained 12S sequences from 77 fish specimens for 36 northwestern Atlantic taxa not well documented in GenBank. Using these and existing 12S records, we designed GoFish assays for 11 bony fish species common in the lower Hudson River estuary and tested seasonal abundance and habitat preference at two sites. Additional assays detected nine cartilaginous fish species and a marine mammal, bottlenose dolphin, in southern New York Bight. GoFish sensitivity was equivalent to Illumina MiSeq metabarcoding. Unlike quantitative PCR (qPCR), GoFish does not require tissues of target and related species for assay development and a basic thermal cycler is sufficient. Unlike Illumina metabarcoding, indexing and batching samples are unnecessary and advanced bioinformatics expertise is not needed. From water collection to Sanger sequencing results, the assay can be carried out in three days. The main limitations to this approach, which employs metabarcoding primers, are the same as for metabarcoding, namely, inability to distinguish species with shared target sequences and inconsistent amplification of rarer eDNA. In addition, the performance of the 20 assays reported here as compared to other single-species eDNA assays is not known. This approach will be a useful addition to current eDNA methods when analyzing presence/absence of known species, when turnaround time is important, and in educational settings.