RESUMO

The common snook Centropomus undecimalis is one of the main commercial fish species in the Caribbean region, including Colombia, where its populations have drastically decreased due to overfishing and environmental degradation. Thus, there is a market imbalance between the availability of snook products and their demand by consumers, which creates an opening for fraudulent actions such as species substitutions. Legislation in Colombia (and most Caribbean countries) lacks effective tools for the easy and rapid detection of frauds. Furthermore, there are very few studies published in scientific journals addressing this issue, of which none include C. undecimalis as the target species. Therefore, in order to investigate the existence of mislabeling in common snook products in Santa Marta, the present study analysed 44 frozen snook fillets from the five commercial brands available in the city. Moreover, 15 fresh snook fillets from six of the main fish markets were also analysed. To discover the frequency of possible frauds in labeling, samplings were carried out in July, September and November of 2019. Sample analyses involved the identification of each fillet at species level through molecular barcodes (16S-rRNA and COI), whose sequences were verified using BLAST and BOLD, and corroborated by a phylogenetic analysis. As a result, an astonishing 98% of the supermarkets fillets were found to be fraudulent, contrasting with a single case registered in the fish shop samples. The species used to substitute snook include the Pacific bearded brotula Brotula clarkae (38 samples), the Nile perch Lates niloticus (4 samples) and the acoupa weakfish Cynoscion acoupa (1 sample). Based on these results, there is a high rate of fraudulent labeling in the marketing of common snook in the city of Santa Marta, which calls for urgent actions to be taken by the corresponding authorities.

RESUMO

La entomología forense es una disciplina que utiliza insectos para obtener información útil en la determinación del intervalo postmortem (IPM). Las moscas de la familia Calliphoridae son muy utilizadas en entomología forense, sin embargo, su identificación a nivel de especie puede dificultarse cuando el individuo se encuentra incompleto o en estadio inmaduro. En el presente trabajo, se evaluó el potencial de la región ITS2 del genoma nuclear para la identificación de especies de Calliphoridae en Colombia utilizando tres aproximaciones: comparando distancias genéticas utilizando la metodología de códigos de barra, haciendo una reconstrucción filogenética, y con enzimas de restricción (PCR-RFLPs). Se secuenciaron un total de 520 pb en 44 individuos pertenecientes a 16 especies. Se calcularon los valores de distancia intraespecífica e interespecíficas utilizando el modelo K2P. Los valores de distancia intraespecífica oscilaron entre 0 y 0,252 %, mientras que las distancias interespecíficas fluctuaron entre 3,6 y 18,9 %, evidenciándose que esta técnica puede ser utilizada como código de barras genético en la identificación de especies de la familia Calliphoridae. Tanto en los análisis de Neighbour-Joining como en los análisis bayesianos el 90 % de los géneros presentan una monofilia sustentada en probabilidad posterior de 0,89 a 1. En todos los casos la especie Blepharicnema splendens agrupa con el género Lucilia. Con base en las secuencias obtenidas se utilizó la aplicación NEBCutter para identificar cuatro enzimas de restricción las cuales se probaron en el laboratorio y se comprobó su utilidad para la identificación rápida de especies de Calliphoridae en Colombia.

Forensic entomology is a discipline that uses insects to obtain useful information for the determination of the postmortem interval (PMI). Flies of the family Calliphoridae are extensively used for this purpose, however, the identification of these flies can be difficult when the individual is not an adult or when it is incomplete. In the present work, we tested the utility of the ITS2 region of the nuclear genome for the identification of Calliphoridae species in Colombia using three approaches: comparing genetic distances using the barcoding methodology, with a phylogenetic reconstruction, and with PCR-RFLPs. We sequenced 520 bp in 44 individuals belonging to 16 species of califorids. Intraspecific and interspecific distance values were calculated using the K2P model. The intraspecific distance values ranged between 0 and 0.252 %, while the interspecific distance values ranged between 3.6 and 18.9 %, indicating that this gene can be used as a genetic barcode for the identification of species of the Calliphoridae family. Both the Neighbour-Joining and Bayesian analyses recovered 90 % of the genera as monophyletic, with pp values between 0.89 and 1. Blepharicnema splendens was always recovered within the Lucilia genera. Based on the obtained sequences we used the NEBCutter application to identify four restriction enzymes that cut in a differential way and generated useful patterns for the identification of the species. The enzymes were successfully tested and confirmed the utility of this technique as a fast way to identify species of Calliphoridae in Colombia.