Schyzocotyle acheilognathi, known as the Asian fish tapeworm (AFT), was first identified in the intestine of Acheilognathus rhombeus from Lake Ogura in Japan (1). Since its initial discovery, the taxonomic classification of this species has remained complex. It has been assigned various synonymous names, likely due to the presence of conspecific cestodes that share a characteristic heart- or arrow-shaped scolex with narrow, deep attachment grooves known as bothria. These morphological traits are also common to the genus Clestobothrium within the family Bothriocephalidae. These morphological similarities have led to the description of different species across various genera, hosts, and regions (2), including Botriocephalus opsalichthydis, B. fluviatilis, B. gowkongensi, B. (Clestobothrium) kivuensis, B. sinensis, B. phoxini, B. aegyptiacus, Ptychobothrium chelai, P. khami, P. duscusae, P. phuloi, P. rojanapaibuli, Capoorai barilii, and Coelobothrium oitense (2–7). The most commonly used name is Bothriocephalus acheilognathi; however, a comprehensive molecular phylogenetic analysis of the family Bothriocephalidae indicated that this species belongs to a separate genus, S. acheilognathi (8).

The cestode species Schyzocotyle acheilognathi is a parasite native to East Asia that has recently spread extensively across all continents except Antarctica (9). This spread is mainly attributed to the import of common carp (Cyprinus carpio) and grass carp (Ctenopharyngodon idella) for aquaculture proposes (2). Moreover, the unregulated trade of ornamental fish and minnows (families Cyprinidae and Leuciscidae), often used as bait, has contributed to the rapid worldwide dispersion of Schyzocotyle acheilognathi (10, 11). Since its first report in Japan, S. acheilognathi has spread to various countries in Asia, initially reaching China (3) and Sri Lanka in 1960, where it was identified as B. gowkongensis in Systomus sarana (12). It was later documented in India, Korea, Nepal, Malaysia, the Philippines, Thailand, Turkey, and Uzbekistan (13–20). In Europe, S. acheilognathi was first recorded in Cyprinus carpio in Ukraine (21), followed by its spread across nearly the entire continent (2). In North America, the first record dates back to 1975 in the United States (Arkansas), where it was found in two cyprinid species, Notemigonus crysoleucas and Pimephales promelas. It is suggested that the introduction of the alien species S. acheilognathi in the continent probably occurred through the importation of grass carp (Ctenopharyngodon idella) from Malaysia and Taiwan in 1963 (22). Subsequently, its presence was reported in other places such as Mexico, Canada (16), and Central America, specifically in Guatemala, Honduras, and Panama (23, 24). In South America, the distribution of the AFT is limited to Patagonia in Argentina and Brazil, specifically in the species Cyprinus carpio (25, 26). However, a recent study has documented the first record of the AFT in a native Brazilian species, the scaleless Rineloricaria pentamaculata (Siluriformes) (27).

Since its initial identification, S. acheilognathi has been recognized as a significant pathogen in Asian and European fisheries (28), causing considerable economic losses of captive-raised juvenile fish (29, 30). The host fish species of the AFT are distributed across tropical, subtropical, and temperate regions. The cestode species S. acheilognathi is considered thermophilic, with an optimal reproduction temperature ranging from 25 to 30°C (31). However, it has also been reported in areas with lower temperatures, where development occurs notably slower below 12°C (2) (Figure 1).

The AFT follows a simple bothriocephaliid heteroxenus life cycle involving two hosts (Figure 2): planktonic copepods (Copepoda: Cyclopidae) as intermediate hosts and freshwater fish as definitive hosts. A diverse range of fish species has been reported as definitive hosts (2), with the number increasing over recent decades (32). In addition, the AFT has been documented in other vertebrates, including amphibians, reptiles, and birds. There have also been reports of parasite eggs in human feces (33). However, these cases should be interpreted with caution as they might have resulted from post-cyclic or accidental transmission (2).

The life cycle of S. acheilognathi is completed in approximately one month. The adult parasite attaches to the intestine of freshwater fish and releases non-embryonated, operculated eggs into the water through feces. Depending on the water temperature, within a few days, an embryo (oncosphere or six-hooked hexacanth) forms inside the egg (9). The hexacanth embryo is enveloped within a ciliated embryophore called a coracidium, whose surrounding ciliated cells enable active movement in water until it is ingested by copepods of the genera Acanthocyclops sp., Cyclops sp., Macrocyclops sp., Megacyclops sp., Mesocyclops sp., Thermocyclops sp., and Tropocyclops sp. (34). Upon ingestion by copepods, the coracidium sheds its ciliated cells, penetrates the gut into the coelom, and develops into a larval stage called plerocercoid. The duration of plerocercoid larvae development depends on water temperature, taking approximately 21–23 days at 28–29°C and approximately 1.5–2 months at lower temperatures of 15–22°C (31).

The life cycle continues when fish ingest copepods infected with plerocercoids. Once inside the fish’s intestine, the plerocercoids attach to the intestine wall and complete their development into the adult stage, producing eggs over a period of approximately 20 days (31).

Colombia is home to a rich diversity of freshwater fish, but their conservation is threatened by multiple factors, including deforestation, pollution, and mining activities. In addition, the introduction of exotic/alien species (neozoans) has further exacerbated the situation (45). These species can significantly affect native fish through direct competition, predation, and habitat alteration. They can also influence disease dynamics (39) by introducing new parasites and pathogens (46). This is the case with Cyprinus carpio, a species that, in addition to altering the ecological characteristics of aquatic ecosystems (47, 48), is considered the primary vector responsible for the global spread of the parasite S. acheilognathi from Asia to the rest of the world. Furthermore, its presence in Colombia, where it is considered one of the most abundant invasive species in the region (49), especially in the Grande River, a tributary of the Porce River, may have contributed to the introduction of S. acheilognathi into the country.

The detection rate of S. acheilognathi in the Porce River basin is particularly alarming. This river flows 247 km northward before merging with the Nechí River, the Cauca River, and the Magdalena River, which ultimately empties into the Caribbean Sea. The Magdalena-Cauca basin is the most representative river system in the northern Andes, with 238 recorded fish species (50). At a global level, it hosts a high degree of ichthyofaunistic endemism, driven by the diverse climatic conditions to which these species have adapted (51). As the main axis of social, economic, and industrial development in the country, this basin faces multiple pressures that impact both the conservation of aquatic ecosystems and fish populations (52). In addition, the first record of the Asian tapeworm (S. acheilognathi) in the Porce River basin poses an additional threat to native species. Considering that S. acheilognathi has spread rapidly, it is highly likely that this parasite will disperse from the Porce River to the entire Magdalena-Cauca basin, thereby exposing fish to a pathogen known for its high transmission rate and adaptability to different thermal zones and hosts. Furthermore, S. acheilognathi is recognized as an important pathogen in aquaculture, capable of causing mortality in farmed species, making it a potential threat to the health of native ichthyofauna in the Magdalena-Cauca basin. The closest report of S. acheilognathi to Colombia is from Panama, supported by morphological evidence and sequence data from the ITS-1 region of the rRNA genome. The AFT case report was conducted on two species of cichlid fish, Aequidens coeruleopunctatus and Cryptoheros panamensi. Although these findings represent the geographically closest reports of S. acheilognathi to Colombia, transmission to the Porce River basin, where it was detected in Colombia, is not feasible due to the geographic isolation between the two basins. Therefore, direct transmission from Panama to Colombia is not possible.

Accurately identifying S. acheilognathi has historically been challenging, since some genera within the family Bothriocephalidae share morphological traits, leading to frequent misclassification of species from different genera and the assignment of incorrect scientific names. However, advancements in research and molecular parasitological identification techniques now allow for more precise verification of these findings. In this study, genetic sequences that showed high similarity percentages with previously reported S. acheilognathi sequences were obtained (8, 53), corresponding to the following markers: ssrDNA, small subunit (18S) nuclear rDNA with 98.55% similarity; lsrDNA, partial large subunit (28S) nuclear rDNA with 99.94% similarity; and rrnL, partial large subunit (16S) mitochondrial rDNA with 99.93% similarity. These genetic sequences were analyzed to confirm the identification of S. acheilognathi. As a result, this research presents the first published sequences of S. acheilognathi from Colombia.

By combining both morphological and molecular evidence, this study documents the first record of the invasive parasite S. acheilognathi in Colombia and its initial detection in the native fish species Parodon magdalenensis. Although this species is currently classified as Least Concern on the IUCN Red List, the potential threat posed by S. acheilognathi highlights the need to integrate parasitological data into conservation policies for this species. Future research should focus on mapping the geographic distribution of S. acheilognathi in Colombia, assessing the genetic variability of its populations across different hosts and locations, and evaluating its impact on the health of native species.