The revenue from fisheries and aquaculture in Thailand accounts for 10% of all agricultural sectors and 1% of the country’s GDP (Fishery Economics Group 2019). The projection in growth of aquaculture in Thailand from 2016 to 2030 is estimated at 36% (FAO 2018), indicating the continued expansion of this sector in the near future. Thai aquaculture relies not only on finfish species, but also shellfish, of which the introduced Pacific white shrimp, Penaeus vannamei Boone, 1931, and black tiger shrimp, Penaeus monodon Fabricius, 1798, dominate coastal aquaculture (Boyd et al. 2017), while the giant freshwater prawn Macrobrachium rosenbergii (De Man, 1879) is raised in inland farms (Kwangkhang et al. 2019). In addition, the Australian redclaw crayfish (RCC) Cherax quadricarinatus (von Martens, 1868) was introduced for culture in Thailand around the year 2000 for the aquarium trade, domestic consumption and export (Soowannayan et al. 2015; Chaichana and Wanjit 2018).

Other non-indigenous crayfish species, e.g., Procambarus clarkii (Girard 1852) and Cherax destructor (Clarke 1936), have previously been introduced to Thailand for ornamental purposes, but their presence in the natural environment has never been reported. However, RCC has been found extensively in some rivers and reservoirs in recent years, although the reports haven’t yet suggested any established populations (Chaichana and Wanjit 2018; Musikasinthorn 2020). A high proportion of introduced crayfish species have shown the ability to thrive and develop self-sustaining populations in new environments, including RCC (Gherardi 2012; Haubrock et al. 2021; Yonvitner et al. 2020). The characteristics of RCC as a large and physically robust omnivorous species with moderate fecundity and broad tolerance to environmental conditions also imply that this crayfish can invade and become established in natural habitats of Southeast Asia, as has occurred already in Singapore and in Indonesia, where RCC has dispersed throughout the country (Ahyong and Yeo 2007; Patoka et al. 2018; Zeng and Yeo 2018; Akmal et al. 2021). Haubrock et al. (2021) reported that RCC has established wild populations in 6 out of 9 countries where it has been introduced in Africa, 7 out of 16 countries in the Americas, and 2 out of 18 countries in Europe. Snovsky and Galil (2011) note that RCC can wander into nearby ponds and drainage canals if there is no appropriate barrier to contain them. Concerns over escaped RCC include their impacts on native species, in particular via predation, alteration of community structure and spread of pathogens; these outcomes already been experienced in many countries (e.g., Ahyong and Yeo 2007; Marufu et al. 2014; Hsieh et al. 2016; Tapia-Varela et al. 2020). Studies of other introduced crayfish species revealed that once they establish in new environments, they may disperse rapidly, which makes their eradication or control extremely difficult and expensive (Gherardi 2012; Patoka et al. 2018).

The potential of an introduced species to become invasive depends on how well it grows and survives in the new environment. If environmental conditions are suitable, biotic resistance may still provide a means to inhibit establishment or spread of the introduced species. Biotic resistance can be either from the biodiversity of the ecosystem (i.e., the higher the biodiversity, the more the resistance against non-native species), or from predators or strong competitors of the introduced species (Britton 2012; South et al. 2020). The presence of predators can result in sub-lethal, long-term effects on the invasive species such as reduction in growth, reproduction and survival (Gherardi 2012). A successful invasive species must further outcompete trophically and functionally analogous native species for limited resources. . Competition between the invader and native species, as well as interspecific competition among invaders, can be examined by additive and substitutive experiments with different density combinations (Britton et al. 2011).

Lynas et al. (2007) hypothesized that RCC could outcompete Macrobrachium prawns, which are both ecologically and economically important, in inland water bodies in Thailand. Moreover, the negative effects of RCC on paddy fields are a serious concern in Thailand, in particular due to its ability to damage developing seedlings and consequently reduce production (Anastácio et al. 2015). Ngamniyom et al. (2019) reported that RCC that inhabit natural freshwaters in Thailand may harbor endoparasites such as metacercaria of the trematode Pseudolevinseniella anenteron, and ecto- and endosymbionts, such as temnocephalans Diceratocephala boschmai and Temnosewellia sp. Moreover, laboratory results in Thailand showed that RCC is susceptible to yellow head virus and white spot syndrome virus, which can be transmitted to native shrimp species such as the black tiger shrimp, one of country’s most valuable coastal aquaculture products (Soowannayan et al. 2015). Chaichana and Wanjit (2018) reported that Thai farmers who raised RCC had a basic knowledge of its biology and culture practices, but little awareness or understanding of the impacts of this crayfish once escaped into natural waters. As a precautionary approach, the Department of Fisheries of Thailand implemented zoning and registration of all RCC farmers in October 2015 to restrict the culture of this crayfish.

Haubrock et al. (2021) reviewed the invasive potential of RCC in tropical and subtropical biodiversity hotspots and pointed out the need for empirical studies to address the potential impacts of this crayfish. Although predicting the potential impacts of an exotic species is quite complicated (Larson and Olden 2012), knowledge of its growth performance and feeding competition is instrumental in understanding how successful they might be in a novel environment (Gherardi 2012). Understanding the risks of RCC is quite important in Thailand, where at least 23 exotic aquatic animal species have already become established in natural habitats (Musikasinthorn 2020). Given that several non-indigenous crayfish species are known to have established populations in a variety of habitats and geographical locations, this work aims to (a) evaluate the growth performance of RCC in near-natural conditions relative to RCC raised in captive conditions, and (b) investigate how successfully escaped RCC can compete with native species present in the limited area and vice versa, using a biotic resistance test and an additive–substitutive experiment, respectively.

All experiments were conducted at the fish farm of Ubon Ratchathani University, Ubon Ratchathani Province, Thailand. Ubon Ratchathani has a tropical wet and dry climate and consists of 3 seasons, namely summer (from March to June), rainy season (from July to October) and winter (from November to February). The annual mean maximum and minimum temperatures are around 35 °C and 20 °C, respectively (Lebel et al. 2020).

At the end of the growth experiment, mean length and weight of RCC (Figure 1) from the earthen pond treatment were greatest (15.4 ± 0.8 cm and 97.3 ± 4.8 g), followed by the concrete tank (13.8 ± 0.6 cm and 65.4 ± 3.6 g) and the natural treatment (10.9 ± 1.5 cm and 32.4 ± 4.5 g). The estimated LWRs (Figure 2) for all RCC groups all had high coefficients of determination (R² > 0.90). The “b” coefficients of LWRs for RCC grown in culture treatments (pond, tank) were greater than 3, indicating positive allometric growth. In contrast, negative allometric growth was found for the natural system (b < 3). ANCOVA was based on length because this parameter showed less variation than weight in each month, and the assumptions of ANCOVA were met. Regressions between month and length for all three treatments showed homogeneity of regression slope (P = 0.054) and variance (P = 0.072). The ANCOVA results revealed significant difference in length among the three RCC groups (P < 0.001). The Bonferroni post-test showed no statistical difference between the samples from concrete tank and earthen pond treatments (P = 0.080), but the natural treatment differed from the two culture systems, i.e., concrete tank (P < 0.001) and earthen pond (P < 0.001).

There was no significant difference in the initial weight of RCC reared as invaders at 30 days (before introduction) in each treatment (F_4,10 = 1.355, P = 0.316). There was also no statistical difference in %SGR of these RCC among treatments (F_4,10 = 0.896, P = 0.501; Figure 3A) at 30 days, with the overall average %SGR of 3.84 ± 3.11%. These RCC were then introduced according to their assigned treatment and raised for 60 more days. The %SGRs of the introduced RCC differed significantly among treatments at the end of the experiment (Figure 3B; F_4,10 = 49.758; P < 0.001) and ranged from 2.06 ± 0.25% (interspecific competition at high density) to 3.40 ± 0.09% (control). Three of the four orthogonal contrasts in this experiment (Table 3) showed significant differences in %SGR. The interspecific treatments showed significantly lower %SGR of introduced RCC than intraspecific treatments (Figure 3B; Table 3; F_1,10 = 48.13; P < 0.001). Significant difference in %SGR of introduced RCC between high and low densities was found in interspecific treatments but not in intraspecific treatments (Figure 3B; Table 3).

For the additive–substitutive experiment, there was no statistical difference among treatments, either in terms of weight of crabs at start (average weight of 2.05 ± 0.05 g [F_4,10 = 1.223, P = 0.361]) or %SGR after 30 days of initial rearing (average %SGR of 2.91 ± 0.14% [F_4,10 = 2.433, P = 0.116; Figure 4A]). The %SGR of the crabs differed significantly among treatments at the end of the experiment (Figure 4B; F_4,10 = 30.442; P < 0.001) and ranged from 0.72 ± 0.01% (intraspecific competition at high density) to 1.58 ± 0.01% (control). Specific growth rate of crabs in the control was significantly higher than the in other treatments (F_1,10 = 58.33, P = < 0.001; Figure 4B; Table 4). The difference in %SGR between interspecific and intraspecific competition was significant, with slower growth when competition was with the same species. Results also showed that %SGR was lower at higher density, both for interspecific and intraspecific competition (P < 0.05; Figure 4B; Table 4).

Certain crayfish species including RCC are ranked among the top invasive aquatic animals globally, and are capable of negative impacts to native residents, habitats and ecosystems due to their plasticity in feeding and other behaviours. Although RCC has become popular as a farmed freshwater crustacean in many countries, Larson and Olden (2012) revealed the high potential of this species to establish populations beyond its native range, particularly in the tropical belt zone (Haubrock et al. 2021). This study, therefore, demonstrates the growth performance of RCC and its potential for competition, as well as likely impacts to native animals that share the same niche (i.e., freshwater crab).

Female and male RCC have similar relative growth, and differences between the sexes are more in body shape than size (Rodríguez et al. 2014; Purnamasari et al. 2018). RCC can grow to marketable size (~30 g) within four months, and males and females can reach 100 g and 70 g within 12 months, respectively, under suitable pond conditions and best farming practices (Jones and Ruscoe 2000). This study reveals that the grow-out system using earthen ponds was most suitable for RCC, which is consistent with the common practice in commercial operations, where broodstock adults are always raised in earthen ponds (Ghanawi and Saoud 2012). Jones (1990) reported that concrete tanks may also be an option for rearing RCC, which is supported by our results, demonstrating no significant difference in growth of RCC between earthen pond and concrete tanks. In contrast, growth of the RCC in the near-natural system was very poor, which could be due to the different availability and quality of food and shelter. The commercial feed used in the culture systems is formulated to be suitable to each stage of RCC growth (Saoud et al. 2013), while the food provided in the near-natural treatment was limited in availability and of possibly lower quality. Growth of RCC observed in the near-natural treatment of this study implies that most of the RCC that have been found in the natural waters in Thailand and Indonesia were about one year old, since their typical sizes were around 10 cm TL (Patoka et al. 2016; Chaichana and Wanjit 2018). The low stocking density treatment in this study shows that crowding may not be the factor limiting growth in the near-natural conditions. Nonetheless, many studies reported that stocking density significantly affected growth of RCC, with higher stocking densities resulting in lower average weight of individuals (Jones 1990; Jones and Ruscoe 2000). Morrissy (2002) mentioned that poor growth of RCC in the wild or intensive outdoor systems could be attributed to the lack of available natural food and/or inadequate artificial feeds. As a consequence of moulting during the early months of life, inappropriate habitat complexity and shelter could hinder the growth of RCC, because social interactions would make them more stressed and vulnerable (Aiken and Waddy 1992; Barki et al. 2006). This idea is supported by the slow increase in length of RCC in the near-natural system of this study compared to the two culture systems.

The regression coefficient “b” from the LWR for RCC in the natural treatment indicates negative allometry (b < 3), unlike the culture systems, which both show positive allometry (Austin 1995; Rodríguez et al. 2002). Negative allometry generally implies that the bodies of large individuals have changed in shape to become more elongated, or that the animals are thinner due to less available food resources or habitat (Damchoo et al. 2021). Purnamasari et al. (2018) showed that RCC from a lake in West Sumatra, Indonesia, also had negative allometry, and that there was no significant difference in LWR between males and females from all stations and all periods of study. Weya et al. (2017) reported that of the four Cherax crayfishes in Papua, Indonesia, only C. snowden had negatively allometric growth, while the remaining three species (C. monticola, C. albertisii and C. communis) showed positive allometry. The authors concluded that the differences were caused by food supply and suitability of the habitat.

Successful invasion of non-indigenous crayfish into a new territory is common because they are often more aggressive and grow faster than the native residents (Hossain et al. 2019; Lopez et al. 2019; Kouba et al. 2021). Studies have shown that many non-indigenous crayfish species have greater resource holding potential and the ability to win agonistic interactions with native residents, with consequent negative effects on the feeding and survival of the native species (e.g., Fořt et al. 2019; Hossain et al. 2019). The resistance of freshwater crabs toward crayfish invasions varies according to geographical area and species involved (South 2020). In this study, the experiments with E. dugasti crabs and RCC showed that the presence of the crabs retarded growth of RCC when reared together, although agonistic interactions between the two species were not clearly observed. This may be due to the less aggressive behavior of these two species compared to other crabs and crayfish (Ng 2017). It is also noteworthy that the RCC occupied the provided shelter more often than the crabs during feeding, which suggests a greater opportunity of the crabs to approach the food. The outcome of agonistic contests between freshwater crabs and crayfish can be predicted by the resource holding potential of each species, which is related to chelae strength (South et al. 2020). Potamiid crabs showed more aggressive and higher resource holding potential than the invasive crayfish P. clarkii in Europe (Mazza et al. 2017), and similar results were found for pseudothelphusid crabs and the invasive RCC in Latin America (Bortolini et al. 2007). South et al (2020) examined the chelae closing force of the potamiid crab and two crayfish species (RCC and P. clarkii) and found that the crab showed significantly stronger maximum chela closing force than the crayfishes.

Higher resource holding potential of native crabs than crayfish might help to control the invasion of RCC in Thai inland waters. However, Zeng et al. (2019) pointed out the matter of body size, in which larger crabs can outcompete smaller RCC and vice versa. They also showed that the competition success of RCC could be predicted by the relative aggressiveness and size difference between the RCC and native crab residents. Potential risk of pathogen transmission from host crayfish to crabs may also reduce the competitiveness of native crab residents (Putra et al. 2018). Besides freshwater crabs, a number of native freshwater fishes in Thailand such as Osphronemus goramy and Anabas testudineus may prey on RCC, which may limit the invasiveness of RCC (Chaichana and Wanjit 2018).

Invasive potential of the RCC is of concern worldwide, as it is now the second-most economically important crayfish after P. clarkii, and has been widely translocated (Haubrock et al. 2021). Besides its culture for human consumption, RCC is also popular in the ornamental pet trade in many countries including Thailand (Chaichana and Wanjit 2018; Putra et al. 2018; Musikasinthorn 2020). This study revealed that RCC can grow in natural conditions, though at a significantly reduced rate compared to RCC raised in aquaculture systems. However, the freshwater crab, used as a representative native resident, was able to outcompete the RCC in terms of growth, and could limit the spread of RCC in Thai waters. Acknowledging the importance of food production and income of crayfish farmers, strict controls are imperative to prevent escapes and invasions of RCC. Preventative measures such as limiting the number of farms and traceability regulations are desired to protect the aquatic biodiversity and integrity of local ecosystems.

Research conceptualization: T. Jutagtae and S. Saowakoon; sample design and methodology: T. Jutagtae; investigation and data collection: T. Jutagtae and W. Kwangkhang; data analysis and interpretation: T. Jutagtae and S. Saowakoon; draft manuscript preparation: T. Jutagtae. All authors reviewed the results and approved the final version of the manuscript.

The study was followed the Ethics statements Animal care and all experimental procedures (Animal use license number: U1-03817-2559).