Eustrongylides excisus in fish species caught in the Massaciuccoli Lake (Northwest Tuscany, Italy): Implications for freshwater fish quality and public health

In recent years, nematodes belonging to the genus Eustrongylides spp. have been increasingly reported in Italian lakes and in several freshwater fish species. This work aimed to investigate the occurrence of Eustrongylides spp. in 11 freshwater fish species collected from Massaciuccoli lake (Northwest Tuscany, Central Italy): Black bull-head, Ameiurus melas (Rafinesque, 1820), Goldfish, Carassius auratus (Linnaeus, 1758), Wels catfish, Silurus glanis (Linnaeus, 1758), Thinlip grey mullet Chelon ramada (Risso, 1827), Pumpkinseed, Lepomis gibbosus (Linnaeus, 1758), Common carp, Cyprinus carpio (Linnaeus, 1758), Tench (Tinca tinca) (Linnaeus, 1758), European eel, Anguilla anguilla (Linnaeus, 1758), Largemouth black bass, Micropterus salmoides (Lacepe`de, 1802), Big-scale sand smelt, Atherina boyeri (Risso, 1810), and Stone moroko, Pseudorasbora parva (Temminck & Schlegel, 1846). Overall, 4053 fish specimens (327 large and 3726 small specimens), collected in eight different samplings (July 2020-April 2021), were visually examined, and subjected to artificial digestion. A total of 476 nematode larvae were collected and microscopically identified as Eustrongylides spp. A subsample (10%) of the collected larvae was subjected to molecular analysis through the analysis of the ITS gene region and identified as E. excisus. Quantitative descriptors of the parasite population were calculated using the data collected from the six species that tested positive (A. melas, S. glanis, L. gibbosus, M. salmoides, A. boyeri, C. ramada) and discussed in the light of their dietary habits. This study reports for the first time the presence of E. excisus in S. glanis and juvenile of C. ramada in Italy. The apparent expansion of this zoonotic parasitic nematode in freshwater fish species, possibly related to changes in the lakes' ecosystems, could represent an issue for local economies. Therefore, Control Authorities and Food Business Operators must respond to this emerging hazard with appropriate control measures, to prevent potentially unfit or dangerous products from reaching the consumer.

Automated summary

In recent years, there has been an increasing occurrence of Eustrongylides spp., a nematode parasite, in Italian lakes and freshwater fish species. This study investigated the presence of Eustrongylides spp. in 11 freshwater fish species collected from Massaciuccoli lake in Italy. A total of 476 nematode larvae were identified as E. excisus, and this parasite was found for the first time in Wels catfish and juvenile Thinlip grey mullet in Italy. The expansion of this zoonotic parasite in freshwater fish species could pose economic challenges and requires appropriate control measures.