Discordance in the identification of juvenile pink shrimp (Farfantepenaeus brasiliensis and F. paulensis: Family Penaeidae): An integrative approach using morphology, morphometry and barcoding

It is most difficult to identify the coexistent commercial pink shrimps Farfantepenaeus brasiliensis and Farfantepenaeus paulensis during the juvenile stage, when secondary sexual characteristics are still in the developing period. Differences in width and/or shape of the dorsal furrow on pleonite six has traditionally been the primary character used to discriminate juveniles of these two taxa, but is unreliable. This study aimed to test the hypothesis that the taxonomic morphological characteristics traditionally used to discriminate between these species are not effective for juveniles. Molecular analyses showed that the COI gene is an efficient marker for separating these two species and that traditional characteristics do not allow for the correct identification of juveniles of these species. In addition, we found that only 64% of juveniles identified a priori based on traditional morphological traits and subsequently verified molecularly were identified correctly. After molecular identification of the species, we searched for new morphological traits that could be used for reliable identification of juvenile and adult stages using morphometry and comparative morphology. The carapace length (CL) ranged from 12.5 to 26.9 mm in F. brasiliensis and from 9.4 to 49.5 mm in F. paulensis. We affirmed the efficiency of COI as a molecular marker and identified a new morphological trait that will aid in the discrimination of juveniles of F. brasiliensis and F. paulensis. Contrary to our expectations, the characters identified by morphometric analysis were subtle and difficult to apply in field identification situations. However, when analyzing the external morphology of juveniles, it was possible to identify differences between the species in the anterior margin of gastrofrontal carina in relation to the rostrum teeth. In addition to corroborating the difficulty in identifying these two species, our study confirms the importance of the association between molecular and comparative morphology analyses in a fisheries and biodiversity context. Furthermore, we extended the geographic distribution of Farfantepenaeus subtilis through a new record from southern Cananéia, on the southern coast of São Paulo State.