If you assume that:

No it isn't perfect... But it does provide a hypothesis when species ID is not known a priori...

Maybe this article can help. - https://www.ncbi.nlm.nih.gov/pubmed/15726991

Mitochondrial cytochrome b DNA sequence variations: an approach to fish species identification in processed fish products. Pepe T, Trotta M, di Marco I, Cennamo P, Anastasio A, Cortesi ML. J Food Prot. 2005 Feb;68(2):421-5

Regards,

Hi Abhay 

It is. Apart from cytb other mtDNA and nuclear regions can provide you with information about intra- and inter-specific variability.

The proteomics approach is developing very quickly, but the current information is still limited.

best regards

If you assume that:

No it isn't perfect... But it does provide a hypothesis when species ID is not known a priori...

In addition to what Tyler writes (and I subscribe), empirically it seems to me that marine fishes are often successfully identified with barcodes, linking eggs and larvae to adults, etc.

However, this is not always the case with freshwater fishes. I know of several perfectly good species that are not told apart by gene COI.

DNA barcoding is a useful tool, but it doesn't always provide definitive results. If you are conducting a relatively detailed taxonomic assessment of a particular group, then barcoding can be useful for identifying lineages and for flagging potentially cryptic species within the group. If you are just comparing your barcodes with entries in online databases, you need to be careful - some sequences are from misidentified species. Furthermore, if you have any new (undescribed) species in your sample, they might show a close match with congeners in these databases.