Commonly known as suckermouth armored catfishes or pleco, Pterygoplichthys spp. are a group of invasive fishes that are widely distributed in several countries, including Mexico. This paper reports the first records of suckermouth armored catfishes in the Candelaria River, thereby expanding its distribution within the Yucatan Peninsula. Fifteen individuals were collected from three sites in the upper and middle parts of the basin. They represented two phenotypically distinct species of catfishes: (vermiculate) Pterygoplichthys disjunctivus (Weber, 1991) and (spotted) Pterygoplichthys pardalis (Castelnau, 1855). Adults and juveniles were caught in lotic ecosystems in 2023 during the dry and rainy seasons. Results suggest that the invasive process of the Candelaria River is linked to the San Pedro River upper basin, in El Petén, Guatemala, through floodings enhanced by hurricanes, allowing these species to disperse. These records highlight the importance of connectivity between adjacent watersheds for the dispersal and expansion of these invasive fishes, mainly from rivers neighboring Guatemala. However, further research is necessary to explore the dynamics and connectivity between aquatic ecosystems and the possible mechanisms that promote the invasion of these fishes in this region.

alien species, Candelaria River, connectivity, dispersion, Guatemala, Mexico

The suckermouth armored catfishes are freshwater fishes native to Costa Rica, Panama, and South America and representing the Loricariidae family, the most diverse of the Siluriformes (see Nelson et al. 2016). Several species of loricariids are commercialized and are of economic interest as aquarium fishes (Courtenay and Stauffer 1990; Hoover et al. 2014). They are commonly known as pleco or loricariids, and including the genus Pterygoplichthys Gill, 1858 (see Mendoza et al. 2009). These suckermouth armored catfishes are invasive species that have been introduced into various freshwater ecosystems in different countries. Their establishment and dispersal have been promoted through aquaculture, aquarium practices, and even by biocontrol efforts, causing diverse ecological, economic, and social impacts in aquatic ecosystems (Mendoza et al. 2009; Hoover et al. 2014).

In Mexico, the first record of the suckermouth armored catfish was in 1995 in the Mezcala River in the Balsas basin in Michoacán; subsequently, its presence was recorded in other localities in the Grijalva, Usumacinta, and Balsas River basins (Mendoza et al. 2007). Currently, Pterygoplichthys spp. are widely distributed, mainly in the southeastern part of the country. High abundance and wide distribution of these species have been reported in aquatic ecosystems in the Usumacinta River basin (Soria-Barreto et al. 2018) and in the lower part of the Grijalva–Usumacinta basin in the state of Tabasco (Sánchez et al. 2015). In these aquatic ecosystems, the suckermouth armored catfish has successfully established itself, modifying the riverbanks to construct its nests (Lienart unpublished¹).

The suckermouth armored catfish was absent from the Yucatan Peninsula until 2006 (Wakida-Kusunoki and Amador-del Angel 2008). The first records were in effluents of the Usumacinta River: the San Pedro and San Pablo River, which is the western limit of the Yucatan Peninsula, and in the delta of the Palizada River at Laguna de Términos (Wakida-Kusunoki and Amador-del Angel 2008). Later, its presence was recorded in the Pom–Atasta fluvial lagoon system in Laguna de Términos (Ayala-Pérez et al. 2014). In these aquatic ecosystems, suckermouth armored catfishes are an abundant component of the ichthyofauna (Wakida-Kusunoki and Amador-del Ángel 2011) and have established reproductive populations (Ayala-Pérez et al. 2014). They have exhibited changes in density associated with seasonal changes in the area. For example, during the rainy season, the overflow of the Palizada River allows young suckermouth armored catfishes to colonize nearby pools, in which it interacts with local fish fauna (Escalera-Vázquez et al. 2019).

In recent years, there has been evidence of the eastward dispersion of the armored suckermouth catfishes in the Yucatan Peninsula. For instance, in the Hondo River (Mexico–Belize), the dispersion and establishment of P. pardalis was documented over one year. The invasion process was favored by flooding and inter-basin connectivity, mainly from Lake Petén in Guatemala (Schmitter-Soto et al. 2015). Similarly, Álvarez-Pliego et al. (2015) reported that the armored suckermouth catfish is already present in the Chumpan River basin. The invasion source seems to be associated with the Grijalva–Usumacinta basin, a nearby watershed, through an eastward dispersal process across Laguna de Términos. Thus, it is necessary to increase sampling efforts in unexplored aquatic ecosystems to verify the presence of these invasive species, as well as to evaluate their possible effects on environmental variables and the aquatic communities it invades. Therefore, a fish survey was conducted in the Candelaria River basin, the largest basin in the Yucatan Peninsula, to document the presence of suckermouth armored catfishes.

Study area. The study area was in the Candelaria River in the Yucatan Peninsula, Mexico. The Candelaria River is a basin shared by Guatemala and Mexico. It originates in El Petén in northern Guatemala, flows through the western portion of the state of Campeche in Mexico, and drains into the Natural Protected Area for Flora and Fauna Laguna de Términos, a large brackish lagoon in the Gulf of Mexico. In Guatemala, the river runs for approximately 50 km, and the basin covers 1158 km² of its surface area (Gunn et al. 1995). In Mexico, the river is 150 km long, and the basin has a surface area of 10525 km² (CONAGUA 2018). The basin is in a semi-karst zone of the Yucatan Peninsula, characterized by the presence of lagoons, rivers, cenotes, and groundwater sources (Gunn et al. 1995). The river flows through rainforest areas and wetlands to the coastal zone, which is characterized by the absence of significant topography (Hudson et al. 2005). This area presents a mean elevation of 200 m AMSL, surrounded by hills up to 380 m AMSL on the eastern side (Gunn et al. 1995). The climate is warm and subhumid with summer rains. The air temperature recorded in the town of Candelaria ranges from 24–28°C, and annual precipitation ranges from 1200–2000 mm (INEGI 2010). The Candelaria River is the most important and largest river in the Yucatan Peninsula. The river flows from the southeast to the north and has important tributaries, such as the Rivers Caribe, La Esperanza, and Las Golondrinas (Gunn et al. 1995). According to data from the CONAGUA hydrometric station 30181 Candelaria, from 2012–2020 the flow of Candelaria River varied from 3.2–395.4 m³ · s^–1, with a mean volume of 40.5 m³ · s^–1, with a mean water temperature of 28.4°C and mean dissolved oxygen concentration of 5.5 mg · L^–1. The main channel, the Candelaria River, flows with the Mamantel River into the Panlau Lagoon to the Candelaria–Panlau fluvial lagoon system (Ayala-Pérez et al. 1998; Hudson et al. 2005). In this lagoon system, water temperature ranges between 23.9 to 30.7°C, dissolved oxygen between 3.6 to 6.7 mg · L^–1, and surface salinity between 2.4‰ and 18.2‰² (Ramos-Miranda et al. 2006). Candelaria River plays a key ecological role based on the amount of water it supplies due to the conservation status of its vegetation, the presence of natural reserves, and the low population density (Kauffer 2010).

Sampling and laboratory methods. Sampling was conducted during the dry and early rainy seasons of 2023. Six sites were selected along the Candelaria River (Fig. 1). At each site, temperature [°C], dissolved oxygen concentration [mg · L^–1], conductivity [mS · cm^–1], total dissolved solids (TDS) [mg · L^–1], and salinity [‰] were recorded with a YSI model 556 multiparameter instrument. Fish were caught during the day, using cast nets (2 m diameter and 1 cm mesh; five throws at each site) and gill nets (55 m long × 2.5 m high, 2.5–9.0 cm mesh; four hours at each site). Caught fish were preserved in a cooler box until they were placed in freezers at the Laboratorio en Ecología Acuática y Monitoreo Ambiental (LEAMA) at CEDESU. In the laboratory, each fish was weighed with an Acculab VIC-303 precision balance. The standard (SL) was recorded using a 0.1 mm precision Vernier caliper. The ventral coloration pattern of the vermiculate or spotted allowed taxonomic determination of the species as Pterygoplichthys disjunctivus (Weber, 1991) and Pterygoplichthys pardalis (Castelnau, 1855), respectively (Armbruster and Page 2006). According to the minimum spawning size reported for the Usumacinta River basin, fishes smaller than 195 mm SL were considered juveniles (Lienart unpublished). Subsequently, the specimens were preserved in formalin solution, then washed with running water, and preserved in 70% ethyl alcohol to be deposited in the fish collection of El Colegio de la Frontera Sur (ECOSC) with the following catalog numbers: 14894, 14895, and 14896.

Figure 1. 

Sampling sites of Pterygoplichthys spp. in the Candelaria River basin, Mexico; including Pterygoplichthys records in the Chumpan River basin (Álvarez-Pliego et al. 2015) and aquatic ecosystems in Guatemala (Gaitán et al. 2020).

A total of 15 fish specimens were caught. Eleven fish were caught in two tributaries: ten individuals in the La Esperanza River (17.81768557°N, 90.36463064°W) and one individual in the Caribe River (18.172344°N, 90.738351°W). Four individuals were caught in the main channel of the Candelaria River (18.19723276°N, 91.11979406°W). Fish measured 126.2–257 mm in SL and weighed 39–330 g. Based on ventral pattern five fish were identified as P. disjunctivus and ten as P. pardalis (Table 1, Fig. 2). Adults and juveniles of both species were caught: one adult (reproductive female) and four juveniles of P. disjunctivus; and five adults and five juveniles of P. pardalis.

Figure 2. 

Variation of the ventral pattern of Pterygoplichthys spp. in the Candelaria River basin, Campeche. Vermiculate coloration pattern (P. disjunctivus) (A, B), spotted coloration pattern (P. pardalis) (C–E).

Individuals were caught in environments with rocky and muddy bottoms. The temperatures varied from 28.2 to 30.2°C, salinity from 0.7‰ to 1.3‰, dissolved oxygen concentrations from 2.2 to 6.3 mg · L^–1, electrical conductivity from 1.6 to 2.7 mS · cm^–1, and TDS from 962 to 1772 mg · L^–1 (Table 2).

This work confirms the presence of Pterygoplichthys spp. in the Candelaria River. In Mexico, suckermouth armored catfishes are invasive species, especially in the lower part of the Grijalva–Usumacinta basin (Sánchez et al. 2015; Soria-Barreto et al. 2018). Recently, they have been reported in the Chumpan (Álvarez-Pliego et al. 2015) and Hondo rivers in the Yucatan Peninsula (Schmitter-Soto et al. 2015). Their presence in the Candelaria River suggests a range extension within the Yucatan Peninsula. Only 15 individuals were caught, which suggests that the abundance of these species remains low in the basin. However, the presence of adults in the reproductive stage could facilitate its establishment and fast dispersal (Mendoza et al. 2009).

The habitats showed freshwater conditions, with high values of electrical conductivity and total dissolved solids (TDS), which may be a result of the semikarstic nature of the Candelaria River basin (Gunn et al. 1995). Similar values have been reported by CONAGUA at hydrometic station 30181 Candelaria, and in the lower part of the basin (Álvarez-Pliego et al. 2015). Some sites had a low oxygen concentration (~2 mg · L^–1). However, this parameter is not a limiting factor for these invasive species due to their anatomical and physiological characteristics, which allow them to obtain oxygen from the air (Mendoza et al. 2009; Hoover et al. 2014).

In the Palizada River, the fish gonad maturation is associated with the flooding pulses (Ayala-Pérez et al. 2014). In other aquatic environments, sexual maturation of suckermouth armored catfishes varies between habitats; however, they are likely to breed at smaller sizes (Hoover et al. 2014). For instance, the size at gonadic maturity for 50% of the population reported in the Las Ilusiones Lagoon in the Grijalva River basin was less than 195 mm SL (Hernández unpublished³

). Therefore, it is important to evaluate the population structure and dynamics in the Candelaria River basin.

The ventral vermiculate or spotted coloration patterns is a key feature to determine organisms as P. disjunctivus or P. pardalis, respectively (Armbruster and Page 2006). However, recent mitochondrial DNA studies have indicated that, although suckermouth armored catfishes have highly variable coloration patterns, all the individuals from the Grijalva–Usumacinta basin belong to the same haplotype and correspond to P. pardalis or for a hybrid origin (Vargas-Rivas et al. 2023). Therefore, it is important to compare genetically individuals to confirm its taxonomy and possible hybridization in this area.

The distribution of the suckermouth armored catfish in the Candelaria River ranges from the middle to the upper part of the basin (Fig. 1). Dispersal and invasion into the Candelaria River basin seem to occur through connectivity with other nearby aquatic ecosystems. In 2014, there was the first record of the suckermouth armored catfish in the Chumpan River, an adjacent basin to the Candelaria River, which flows into the Laguna de Términos. Authors suggested that these species dispersed from the Grijalva–Usumacinta basin, via Laguna de Términos, enhanced by the seasonal variation in salinity and the tolerance to estuarine conditions of Pterygoplichthys (see Álvarez-Pliego et al. 2015). Although, the Panlau Lagoon has low salinity (2.6 ‰) during the nortes season (Ayala-Pérez et al. 1998), which could facilitate its dispersal. Conversely, it seems unlikely that it arrived in the same way as in the Chumpan River. Here salinity in the freshwater–seawater mixing zone has been reported to be higher than 18‰ (Ramos-Miranda et al. 2006), while Pterygoplichthys spp. salinity tolerance is down to 10‰ (Capps et al. 2011). In addition, the suckermouth armored catfish is absent in the lower part of the basin (Álvarez-Pliego et al. 2015).

The highest abundance of suckermouth armored catfishes was recorded in La Esperanza River, near the Guatemala border (Fig. 1). Local fishers and inhabitants mentioned that this invasive fish appeared around 13 years ago, after the hurricane Richard through the Yucatan Peninsula in 2010. This suggests that natural invasion occurs through the hydrological connectivity upstream and allows the dispersal of Pterygoplichthys spp. through this region. Given the topography of the Guatemalan Petén (Gunn et al. 1995), it is likely to get flooded by extreme rainfall caused by hurricanes and connected adjacent watersheds. This could enhance the dispersal process and invasion of Pterygoplichthys spp., through the inter-basin connectivity, as it has been reported for the Hondo River (Schmitter-Soto et al. 2015). If invasion and dispersal are favored by these hydrological events, the presence of suckermouth armored catfishes in the Candelaria River may be a result of the connectivity of aquatic ecosystems, particularly the San Pedro River in Guatemala. Since 2000, the presence of Pterygoplichthys spp. has been reported in Guatemala, and its records have increased; it currently has established populations in five sub-basins in northern Guatemala, including the nearby San Pedro basin (Gaitán et al. 2020) (Fig. 1).

The first record and presence of the invasive fish Pterygoplichthys spp. is reported in the Candelaria River basin, although its abundance is low, it is distributed in the upper and middle part of the basin. Its invasion and dispersal have occurred naturally, promoted by the presence of hurricanes and connectivity between watersheds in the Petén in Guatemala; the San Pedro River is the most likely source. Considering Pterygoplichthys spp. dispersal capacity and its negative effect on aquatic communities and environments, more sampling efforts and studies are required to understand those dispersal mechanisms in this region of Mexico, including spatiotemporal monitoring across the Candelaria basin. Finally, it is important to evaluate its possible effects on aquatic ecosystems and, consequently, on local fisheries.

We thank the Ejidos authorities for access and support during sampling activities at the study sites. We are grateful to Sergio E. Padilla Paz and Mauricio González Soria for generating Figure 1 and Figure 2, respectively. Thanks to Alfonso González for an early revision. MSB thanks CONACYT for the postdoctoral grant. We thank an anonymous reviewer for helpful comments on the manuscript.