Single-species PCR assays accurately measure eDNA concentration. Here we test whether multi-species PCR, i.e., metabarcoding, with an internal standard can quantify eDNA of marine bony fish. Replicate amplifications with Riaz 12S gene primers were spiked with known amounts of a non-fish vertebrate DNA standard, indexed separately, and sequenced on an Illumina MiSeq. Fish eDNA copies were calculated by comparing fish and standard reads.