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Over the past decade, the use o molecular tools for taxonomic identification have increased in response to limitations of morphological identification. Despite considerable efforts, larval identification remains one of the major factors limiting the answer to questions that can be addressed regarding ichthyoplankton studies, such as larval distribution, spawning locations and seasons. These limitations are especially acute within certain regions, for certain taxonomic groups and during the earliest stages of larval development. For fishes the techniques that have been most frequently used, involve the use of polymerase chain reaction (PCR), followed by sequencing or restriction fragment length polymorphism (RFLPs), or PCR of specific primers. In the present study the goal of using PCR-sequencing was to verify the identity of distinct larval types of Engraulidae. Plankton samples were collected at the Upper Gulf of California in March 2011. Zooplankton samples were collected with a surface net, which were fixed-preserved in 80% ethanol. Five Engraulis mordax and five Cetengraulis mysticetus-type larvae were identified using morphometric and meristic data. Adult specimens of seven Engraulidae species were also collected and identified. For molecular identification, genomic DNA was extracted, two mitochondrial DNA fractions, 16 S rRNA (?650 bp) and COI (?750 pb), were amplified using universal primers, and PCR products were sequenced in both directions. Sequences of larvae and adults were compared to estimate genetic distances among them, using the sequence of Anchovia macrolepidota as outgroup. Genetic distances and Neighbor-Joining trees corroborated that five E. mordax-type larvae were effectively such species, but the five C. mysticetustype larvae were not that species, indicating a misidentification of these larvae within the Engraulidae family. In fact, three C. mysticetus-type larvae, showed the same sequence as E. mordax-type larvae. The other two larvae did not matched to any available sequence from our samples or from the GenBank. This is a first report of the presence of E. mordaz larvae at the Upper Gulf of California during March, possibly indicating the expansion of its distribution range and/or reproductive period at the northern Gulf of California. The possible explanation of E. mordax larvae presence in this region is discussed.

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