Amazon sailfin catfish are native to Latin Arica (Siluriformes: Loricariidae: Pterygoplichthys) and are popular around the world as ornamental fish. It is well-documented that these species are highly successful invaders and very prone to forming new geographical ranges. However, once established, eradicating a new population is a very challenging task. In Bangladesh, species of the genus Pterygoplichthys are expected to spread widely and have a severe detrimental impact on ecosystem health, biodiversity and economics. Here we provide new information on the future probable establishment of non-native populations of these species in the wild using a climate-matching analysis and highlight their potential area of occurrence. The potential socio-economic consequences are also discussed, as are the public perception of these species and probable economic damages caused. Control of the import of similar species, their culture and intentional or unintentional release into open water is urgently required.

Pterygoplichthys, fish, biological invasion, modelling, climate matching, Asia

Biological invasions cause huge environmental and socio-economic losses worldwide (Bang et al. 2022). In freshwaters, numerous invasive fish species have been introduced via various pathways such as culture for human consumption, ornamental aquaculture and the pet trade, and pest control (Faulkner et al. 2020). Tropical countries are especially suitable for the establishment of new populations of many fish species such as the well-known invasive Nile tilapia Oreochromis niloticus (Linnaeus, 1758) and common carp Cyprinus carpio Linnaeus, 1758, as well as species paradoxically endangered in their native ranges such as the giant arapaima Arapaima gigas (Schinz 1822), as reported by Marková et al. (2020) and Zambrano et al. (2006). In the case of catfish, several species of Amazon sailfin catfish Pterygoplichthys spp. have been recognized in tropical, subtropical and warm-water regions as invasive (Nico et al. 2012; Rao and Sunchu 2017; Hossain et al. 2018; Orfinger and Goodding 2018; Patoka et al. 2020; Saba et al. 2020; Yen 2021).

Amazon sailfin catfishes (Siluriformes: Loricariidae: Pterygoplichthys) are native to Latin America and are very popular worldwide as ornamental species (Burgess 1989; Hoover et al. 2004; Novák et al. 2022). They are transported around the planet in huge quantities and released accidentally by irresponsible owners or even intentionally by producers for culture in new localities outside their native ranges (Hoover et al. 2014). They can quickly establish new populations where suitable climatic conditions exist and then spread and multiply rapidly (Orfinger and Goodding 2018).

Various biological and ecological characteristics allow certain Amazon sailfin catfishes species to be highly successful invaders: parental care and large eggs that generate strong hatchlings that can escape predators; nesting; extended spawning seasons; high fecundity; rapid growth; lifespans of more than five years; ability to gulp air and extract oxygen through the gut lining in hypoxic environments; and a capacity to survive several hours of desiccation in simple burrows (Armbruster 1998; Hoover et al. 2004; Gibbs and Groff 2014; Hossain et al. 2018). Their scales are hard, and their fins are equipped with sharp hard spines that are effective deterrents against predators (Quan et al. 2020; Peplinski et al. 2021). For this reason, species such as Pterygoplichthys disjunctivus (Weber, 1991) and P. pardalis (Castelnau, 1855), as well as their hybrids, are currently spreading intercontinentally as invaders in the tropics, subtropics and warm-water regions (Hill and Sowards 2015; Hossain et al. 2018; Patoka et al. 2020). Although the most non-native populations originate from aquarium releases or escapes from fish cultures, the possibility of introduction for human consumption cannot be ignored (Patoka et al. 2020). Where these species have been introduced by a combination of several pathways, they can be referred to as ‘polyvectic’ sensu Carlton and Ruiz (2005).

Invasive Pterygoplichthys species can become locally dominant fish species as they have the capacity to outcompete native species by altering the dynamics of food webs (Page and Robins 2006) and by exploiting similar trophic niches (Meena et al. 2016). Various negative impacts on habitats in invaded ranges are also known, including increased water turbidity, bank erosion and instability (Nico et al. 2009a). The grazing and burrowing behaviour of Pterygoplichthys spp. also greatly damages populations of aquatic macrophytes (Hoover et al. 2004; Nico et al. 2009b; Gibbs et al. 2010). Once a new population is established, these fish are very difficult to eradicate (Hill and Sowards 2015; Orfinger and Goodding 2018).

In Bangladesh, Pterygoplichthys spp. were imported for ornamental purposes in the 1980s but escaped into the wild during the 1990s as a result of both intentional and unintentional releases (Hossain 2020). However, no Pterygoplichthys spp. were recorded in Bangladesh until their first appearance in 2007 in northern Bangladesh (Hossain et al. 2008). Recently established wild populations (Parvez et al. 2023) and numerous records at different waterbodies have now been reported (Parvez et al. 2023; Mamun et al. 2023). Before banning all types of activities related to Pterygoplichthys spp. (suckermouth catfishes) in 2023 (Ahamad 2023), there were no legislative restrictions banning imports of these fish into Bangladesh by aquarium traders or other vectors. Explicit permission from the Bangladesh Department of Fisheries, Ministry of Fisheries and Livestock is, nevertheless, required for importing these species (MoFL 2018) and these fish are perceived as a ‘conditional’ species. Conditional non-native species are those that are thought to endanger the environment, native biota and/or humans. However, this regulation seems to be totally ineffective (a so-called ‘dead letter’; Patoka et al. 2018) as aquarium traders import and breed these fish commercially in huge quantities in local hatchery facilities without permission (Hossain 2021). These irresponsible activities and intentional or unintentional ranching in the wild may have led to these species becoming widespread in Bangladesh.

Therefore, these species are expected to become well-established in many areas of Bangladesh and to have had significant negative impacts on biodiversity, ecosystem functioning and economics. To date, the only data on the abundance and wild establishment of Pterygoplichthys spp. in Bangladesh are reports by local people and frequent newspaper articles (Mamun et al. 2023). Therefore, we decided to (i) update information on the occurrence of these fish species in Bangladesh by evaluating the establishment of non-native populations in the wild using a climate-matching model; and to (ii) observe and evaluate human attitudes towards these fish.

We found Pterygoplichthys spp. to be widely spread throughout Bangladesh. Given the recent attention focused on invasive fish species in general and on the illegal releases of Pterygoplichthys spp. in particular by both the general public and the Bangladesh government (Hossain 2020), we recommend that these findings be transmitted to all key stakeholders involved in the sustainable exploitation and conservation of the ichthyofauna of the country.

It is foreseeable that Pterygoplichthys spp. will establish populations in suitable water bodies throughout Bangladesh. Based on the climate-matching maps, we believe that further detailed monitoring is required in the regions indicated as threatened to update current knowledge of the distribution and spread of these catfish in Bangladesh, and to improve the management of water bodies. The climate analysis shows a good climate match for these species for most of Bangladesh. Judging from reports in newspapers and observations by local people, these species are now widespread in the wild in Bangladesh. However, no scientific literature other than the first record from 2007 (Hossain et al. 2008) and a recent invasion note (Mamun et al. 2023 and Parvez et al. 2023) has reported their widespread occurrence in this country or studied habitat suitability via climate-match analysis. Pterygoplichthys spp. in the Indian subcontinent and southern Asia have become established as an invasive population (Patoka et al. 2020; Sinha et al. 2010; Rao and Sunchu 2017; Saba et al. 2020) and the climate analysis and pattern of wild establishment show the suitability of habitats in Asia (Patoka et al. 2020; this study). Little geographical climate difference across the country and high aqueous connectivity through river channels and floodplains during the monsoon and flooding periods have facilitated the spreading and establishment of these species in favourable climatic conditions. The highest occurrence pattern was in 2020–2021 and in open waters (69%), which also indicates that these species are spreading in the wild. Repeated occurrence in the same or nearby localities in consecutive years could be related to well-established populations. Year-wise fluctuations might be due to the reporting pattern of individual cases.

The pathways of introduction into Bangladeshi waters include both intentional and unintentional releases from aquariums that mirror reports from other countries (Page and Robins 2006; Samat et al. 2016). For instance, in Indonesia Pterygoplichthys spp. were introduced to control the invasive water hyacinth (Patoka et al. 2020), while in Bangladesh and the Philippines they were introduced for ornamental purposes by the pet trade (Cagauan 2007). In Bangladesh, introductions mostly derive from ornamental culture facilities in households or commercial pet shops. According to newspaper reports and shop owners’ information, illegal breeding and fry production in Bangladesh (Mobin 2022) probably represents another pathway of introduction into the wild due to surplus production. Another possible pathway of the Pterygoplichthys spp. introduction into Bangladeshi waters was from India during monsoon along connected major river channels (the Gangas and the Brahmaputra rivers) (Hussan et al. 2016). Water connectivity during monsoon, the altitudinal difference from north to south, and the major river channels also facilitate the occurrence of these species in all favourable regions, as well as in those that lie outside the suitable climate-match regions in Bangladesh.

Local people, fishermen and farmers assume that these fish will compete with other indigenous fish and predate on their eggs and larvae. Fishermen and farmers mentioned the reduction in fish availability and total fish production in invaded habitats. This finding also corroborates the statements mentioned by Mamun et al. (2023) and the findings of Parvez et al. (2023). Damage to fishing nets by these catfishes has been also reported. Some interviewees also suspected that native fish species were displaced, and habitat was destroyed by Pterygoplichthys spp. The environmental impact of Pterygoplichthys spp. has been reported by several scientists from other continents (Hoover et al. 2004; Chavez et al. 2006; Wakida-Kusunoki et al. 2007; Cook-Hildreth 2008; Krishnakumar et al. 2009; Chaichana et al. 2013) and in Bangladesh they seem to possess all the characteristics of a successful invader threatening native fish populations (Hoover et al. 2004; Liang et al. 2005; Nonogaki et al. 2007; Wakida-Kusunoki et al. 2007; Krishnakumar et al. 2009; Mendoza et al. 2009). These negative impacts have also been reported by Parvez et al. (2023) via a mesocosm study and highlighted by Mamun et al. (2023) through expert opinions.

Aside from its environmental impact, the Pterygoplichthys spp. invasion has also had a socio-economic effect on local communities. Fishermen are suffering economic losses due to damage to their fishing gear and poorer catches (Chavez et al. 2006; Wakida-Kusunoki et al. 2007; Krishnakumar et al. 2009; Orfinger et al. 2019). This biological invasion of both artificial ponds and open waters reduces fish production, which ultimately affects fish farmers’ and fishermen’s livelihoods. Moreover, there is an obvious related burden on fish farmers caused by the extra cost of pond management due to, for example, the need for dyke repair and pond drainage aimed at eradicating these invaders.

Eradication attempts are not successful because these fish can survive in extremely dry conditions, grow quickly and have high fecundity (Hoover et al. 2004; Chaichanaa and Jongphadungkiet 2012; Hill and Sowards 2015; Hussan et at. 2021). In invaded habitats they destroy ponds’ potential as food sources by sequestrating the majority of the nitrogen and phosphorus and hamper primary production in water bodies (Capps et al. 2009), factors that have led directly to economic losses. People are also frightened of these fish because of the hard armoured shields and spines on the dorsal fin that can cause injury. They are even afraid of bathing in invaded waterbodies, which in turn creates unnecessary stress on people who live near these rivers and ponds and depend on them for bathing and other daily activities. Simply put, the many human activities tied to certain waterbodies are negatively affected by the invasive Pterygoplichthys spp.

In our study, the local people who catch these fish in rivers or other waterbodies throw them onto the bank or release them back into the water. Today, however, the Bangladeshi government is taking note of these invasive fish and is trying to raise awareness amongst the general public and stakeholders regarding the risks and negative consequences of this invasion. For instance, government officials have made several official announcements and came to fish the Buriganga River. All the Pterygoplichthys spp. they caught were officially buried on the bank to encourage people to follow this approach.

The invasive Pterygoplichthys spp. have easily occupied and established themselves in Bangladesh as a tropical region (climate-match result) and can withstand extreme conditions (Hossain et al. 2018). Therefore, both the mass media and government need to work continuously to create greater public awareness regarding the negative impact of these invasive species and to stop intentional releases or unintentional escapes into water bodies (Novoa et al. 2017). Adult fish, eggs and juveniles should be caught/killed in invaded regions periodically by netting or draining wherever possible. Invaded areas could be separated by net-blocking or embankments from uninvaded waters (Hussan et al. 2021) and imports for any purpose of these species should be banned by the government.

However, illegal import and breeding hamper initiatives set up by concerned people. Along with eradication and control strategies, any control measures must consider other aspects of the invasion by Pterygoplichthys spp. In our study, we found that low income and homeless people eat these fish despite the fact that pollution from contaminated rivers and streams can accumulate in their flesh (Elfidasari et al. 2020). However, pollution-free grown Pterygoplichthys spp. could be used to manufacture fish meal, poultry, and cattle feed (McLaughlan et al. 2014; Ragaza et al. 2021). Some researchers also suggest that their skin could be used in handicrafts (Cagauan 2007) and their body parts for making soap, biofuel, enzymes, collagen or natural coagulants to control water turbidity (CEC 2009; Medellín Castillo et al. 2022).

Finally, we should also state that the situation of Pterygoplichthys spp. may in fact be worse in Bangladesh than we observed. The detected frequency of occurrence of these species could be just the tip of the iceberg. The established breeding populations might be present in more localities and open waters than we observed. Thus, based on the climate-matching maps, we suggest that further monitoring of the regions highlighted as suitable for these taxa be performed to update current knowledge of the occurrence, distribution and spread of these fish species in Bangladesh. Moreover, as necessary further steps, the control of imports, culture and releases – whether they be intentional or unintentional – of similar species into open waters is urged. There is hope that the Bangladesh government will ban all types of activities related to the catching, sale, importation, breeding, and production these fish in the country (Ahamad 2023). Nevertheless, strict official monitoring of illegal culture and breeding within the country is needed to stop further spread. Currently, the effective strategy for eradication of these species from the wild still needs to be developed. In addition, the negative impacts discussed in this article and elsewhere (Hossain et al. 2008; Mamun et al. 2023; Parvez et al. 2023) focus on either P. pardalis or P. disjunctivus but not on putative hybrids. In future it will be important to clarify whether both species and hybrids have similar effects on local ecology, social life, and ecosystems. The farmers or fishermen could play a crucial role in eradication through killing unwanted fish or larvae and/or by destroying fish eggs on farms or in open waters whenever found.

MSH was supported by ‘Special Research Grant’ Project (BS-189) of Ministry of Science and Technology, Bangladesh and Research Project (ID-25) of Research Management Wing of Bangabandhu Sheikh Mujibur Rahman Agricultural University, Bangladesh. JP was supported by the Technology Agency of the Czech Republic within the project ‘DivLand’ (SS02030018).

Conceptualization: MSH and JP Methodology: MSH; SGA Formal analysis and investigation: MSH, SGA; Writing - original draft preparation: MSH, JP, SGA; Writing - review and editing: MSH, JP, SGA, MB; Funding acquisition: JP, MSH; Supervision: MSH, JP.

The study did not involve any endangered or protected species. No specific permission was required for the locations and activities involved in this study. All experimental manipulations (rearing, capture and measurements) were conducted according to the principles of the Ethical Committee of Bangabandhu Sehikh Mujibur Rahman Agricultural University, Bangladesh, and the National Research Ethics Committee (NREC) of Bangladesh.

The authors would like to appreciate the University of South Bohemia in České Budějovice, Faculty of Fisheries and Protection of Waters, South Bohemian Research Center of Aquaculture and Biodiversity of Hydrocenoses, Research Institute of Fish Culture and Hydrobiology, Zátiší 728/II, 389 25 Vodňany, Czech Republic, for financing the English editing. The authors would like to thank Mir Mohammad Ali and Abu Hanif for the photographs of the wild caught fish and of the fish with burrow. Special thanks too to Michael Lockwood for the English editing. I would like to also thank the master students for the partial data collection from fisherman. We would like to thank the reviewers for their significant feedback to improve our study. We thank the Editor also for his/her patient aid.