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Snakeheads of Sri Lanka: A Taxonomic and Biogeographic Review

Purpose : Fish species of the family Channidae, commonly known as snakeheads, represent biggest and most caught native freshwater species in Sri Lanka. Despite importance for biodiversity and fisheries in Sri Lanka, members of this family are one of the least studied on taxonomic status and geographic distribution. Research Method : As an initial step of a study to revise the taxonomy and biogeography of freshwater fish in the family Channidae based on molecular phylogenetic and morphological relationships and biogeographical affinities, authors reviewed all the available published information and examined the specimens available at the National Museum of Sri Lanka. Findings : Six valid species have been recorded; Channa ara (Deraniyagala, 1945), C. marulius (Hamilton, 1822) C. kelaartii (Gunther,1861), C. orientalis Bloch and Schneider 1801 C. punctata (Bloch, 1794) and C. striata (Bloch, 1793). Current review suggests the exiting knowledge on the phylogeny and biogeography of Channidae in Sri Lanka is far from complete, identifying specific gaps to be prioritized in future research. Limitations : Current regional studies on the family Chanidae highlight the importance of a complete systematic revision of Sri Lankan species with an integrative approach. Literature review shows the necessity of a fresh analysis on the distribution data with ecological niche modeling and molecular phylogenetic studies to understand biogeographical and evolutionary history of the family. Originality / Value : Provides a consolidated account of the current knowledge on the taxonomy and biogeography of the Sri Lankan members of the family Channidae.


INTRODUCTION
Snakeheads are described as a group of freshwater fish belonging to family Channidae, characteristically identified by their prominent snake-like head with large scales and the distinct mouth with sharp teeth (Jayaram, 1999;Gurumayum and Tamang, 2016). They are predatory in nature and carnivorous as adults reach comparatively large sizes (i.e. Talwar and Jhingran (1991) was recorded 122cm lengh for Channa marulius) except for few species, vivid colourations in many, and inhabit most countries in Asian region. These characters earned them a reputation as hardy fish easy to grow, and a highly valued, both in food fish industry and ornamental trade worldwide. Same characters are also attributed to their invasive nature in introduced habitats (Courtenay and Williams, 2004). They are characterized by peculiar morphological features, such as an elongated cylindrical body, long and entirely soft-rayed dorsal and anal fins, a large mouth with well-developed teeth on both upper and lower jaws, vomer and palatine bones of the skull, and an accessory air-breathing apparatus known as the suprabranchial organ, as it is situated in the suprabranchial cavity in the head (Talwar and Jhingran, 1991;Jayaram, 1999). The snakeheads (Actinopterygii: Perciformes: Channidae) comprise more than 40 valid species in three genera; Channa, Parachanna and Aenigmachanna (Li et al., 2006;Serrao et al., 2014;Britze et al., 2019;Praveenraj et al., 2019;Sudasinghe et al., 2020a). Snakeheads of the genus Channa are distributed mainly in tropical Asia, and Parachanna in tropical Africa, while Aenigmachanna with only a single species recorded from South India (Li et al., 2006;Britze et al., 2019).
Some members of the genus Channa including C. striata, C. marulius and C. micropeltes are main edible fish across most of the Asia (Willey, 1910;Talwar and Jhingran, 1991;Li et al., 2006;Wimalasena and Jayasuriya, 2013). Being edible, some members of this genus have even been introduced to new geographical areas in Asia as food fish, while a few has been accidentally released into biogeographically new locations via ornamental fish trade. For example, Channa striata has been introduced to Fiji, Papua New Guinea, New Caledonia and Hawaii as a food fish (Li et al., 2006). Mustafa et al., (2013) and Wimalasena and Jayasuriya (1996) have studied the aquaculture and nutritional value of Channidae. Further, genus Channa has been studied not only for its nutritional value, but also for the medicinal value (Mustafa et al., 2012;Mustafa et al., 2013).
The main objective of this review was to comprehensively assess the current status of the family Channidae of Sri Lanka using all available data on the morphological, molecular phylogenetic and distributional aspects of Sri Lankan Channids. Further, it was intended to identify gaps in knowledge related to the taxonomy, and molecular phylogenetic and biogeographic relationships in Sri Lankan members of the family Channidae.
All literature publish on the family Channidae in Sri Lanka were reviewed and discussed in this paper as an initial step of a study to revise the taxonomy and biogeography of Channids. Taxonomic reviews, monographs, species descriptions and other related literature were used to determine the current status of knowledge on the family. Further, we examined the specimens of Channids available at the National Museum of Sri Lanka. Additional details of the review when and where relevant are provided below,

Taxonomy of the Family Channidae in Sri Lanka
Previous work on the taxonomy of family Channidae in Asia including Sri Lanka recognized two genera; Channa Scopoli 1777 and Ophicephalus Bloch 1793. Members of the genus Channa were distinguished from those of the genus Ophicephalus by not having pectoral fins, which however is present only in a single species of Channa, i.e. C. orientalis. In current taxonomic treatments Ophicephalus Bloch 1793 is considered as a synonym of Channa (Pethiyagoda, 1991;Kotteilat, 2013). According to the current and historically published literature on freshwater fishes of Sri Lanka including Gunther (1861), Duncker (1912), Deraniyagala (1929Deraniyagala ( , 1932Deraniyagala ( , 1945Deraniyagala ( , 1952Deraniyagala ( , 1963, Munro (1955), Mendis and Fernando (1962), Senanayake (1980), Pethiyagoda (1991), Goonatilake (2012), De Silva et al., (2015), Goonatilake et al., (2020), and Sudasinghe et al., (2020a) and Sudasinghe et al., (2020b) the genus Channa is represented in Sri Lanka by six valid species viz. Channa ara (Deraniyagala, 1945), Channa marulius (Hamilton, 1822), Channa kelaartii (Gunther,1861), Channa orientalis Bloch and Schneider 1801, Channa punctata (Bloch, 1794) and Channa striata (Bloch, 1793). According to the recent national literature on Sri Lankan Channidae (Goonatilake, 2007, De Silva et al., 2015, Goonatilake et al., 2020, Sudasinghe et al., 2020a, two species of snakeheads, Channa ara, and C. orientalis, are considered as endemic to the island. Lateral line scales, the number of rays in fins, number and size of scales, cephalic scales, absence or relative size of pelvic fins, teeth, relative body lenghth sizes and colourtaion are major taxonomic characteristics which had been used in the taxonomy of Channidae (Gunther, 1861;Deraniyagala,1929Deraniyagala, , 1932Deraniyagala, , 1945Deraniyagala, , 1952Jayaram, 1999;Britz et al., 2017;Sudasinghe et al., 2020a andSudasinghe et al., 2020b). In his treatment of the fishes of Sri Lanka, Deraniyagala (1952) provided the review of the Family Channidae including a key to all Sri Lankan species, also providing an illustrated guide to the scale pattern on the head, which can be used to species level identification ( Figure 01). However, Deraniyagala's (1952) cephalic scalation has not yet been followed up since then, with neither any critiques nor further improvements.. In the description of Channa orientalis (the type species of the genus) by Bloch & Schneider in 1801, its type locality is given as "Habitat in India Orientale", which is in confusion with Sri Lankan endemic status of the species. According to literature, neither Bloch nor Schneider has visited Sri Lanka or India personally, and their work was based on about fifteen hundred specimens in a collection owned by M.E Bloch (Karrer et al., 1994). Bloch has received specimens from all over the world. Hence, it is quite possible that the type specimen of Channa orientalis originally being collected from Sri Lanka may have been received by him with an Indian collection. It can also be argued that he might also have had a doubt about the type locality as it is given with the suffix "Orientale" after India, which represented the entire south and southeast Asian region at that time (Sclater, 1858;Wallace, 1876). Furthermore, in addition to its type locality being confused with India, recently published records of specimens phenotypically presumed by authors as Channa orientalis, from peninsular India questions its endemic status in Sri Lanka (Sarrao et al., 2014;Sharma et al., 2015). However, Mishra et al., (2014) shows that Indian specimens that were treated as Channa orientalis do not belong to the same species and confirmed the restriction of C. orientalis to Sri Lanka. Sudasinghe et al., (2020b) has recently revised the status of Channa gachua of Sri Lanka and south India and re-erected Channa kelaartii as a valid species which is restricted to Sri Lanka and Southern India.
Further, Sudasinghe et al., (2020a) has recently revisited the Channa marulius group of Sri Lanka, where they distinctly identified the population of Mahaweli river as a valid species. The name Channa ara has been assigned referring to the subspecies description of Ophicephalus marulius ara by Deraniyagala (1945). Further, the northern dry zone population of that group was confirmed to remain as Channa marulius, while the southwestern wet zone population has been treated as a taxonomic ambiguity.
Further, a multitude of colour varieties have been recorded from geographically disjunct populations within the island, Channa ara and Channa orientalis needs further investigation at local geographic scale within Sri Lanka. All in all, a considerable level of taxonomic ambiguity exists within the genus Channa in Sri Lanka (e.g. population of Channa ara in the south western part of Sri Lanka has not been included into any valid species, even after the taxonomic revision by Sudasinghe et al., (2020a).
Sri Lankan species of Channa and their current taxonomic status can hence be summarized as follows;

Ophicephalus marulius Hamilton, 1822
Type locality: Gangetic provinces, India Ophicephalus marulius ara (Deraniyagala 1945) Type locality: Ceylon Channa cf. ara Sudasinghe et al., 2020 Type locality: Southwestern wet zone of Sri Lanka Further taxonomic studies, especially those involving molecular techniques are needed to clarify the status of the southwestern wet zone population of Channa cf. ara (Sudasinghe et al., 2020a). Further a detailed reassessment of the taxonomic history and biogeographic limits of C. ara and C. marulius would result in taxonomic stability of the C. marulius group in Sri Lanka.

4.
Channa orientalis Bloch and Schneider 1801, Type locality-India "orientale", Although, few Indian publications (Jayaram, 1999;Sharma et al., 2015) have mentioned the occurrence of Channa orientalis in Indian mainland, molecular genetic studies have revealed the species as a distinct lineage endemic to Sri Lanka (Conte-Grand et al., 2017). Multiple authorships exist for the species C. orientalis in previous publications, i.e. in Mendis and Fernando (1962) as 'Bloch' and in Jayaram (1999) as 'Schneider'. Karrer et al., (1994), reviewed the original work by Bloch and Schneider and suggested authorship for the taxon as "Bloch and Schneider 1801".

Ophicephalus punctatus Bloch, 1794
Type locality-Malabar Coast A common freshwater species in Sri Lanka and widely distributed from Afghanistan to southern China including India, Pakistan and Bangladesh. According to Conte-Grand et al., (2017), this species is characterized by deep intraspecific divergences and hence could be split into multiple lineages. Further, Sri Lankan population of C. punctata is yet to be genetically evaluated to ascertain its identity.

Geographical distribution of the Family Channidae in Sri Lanka
Genus Channa is distributed from Iran, Afghanistan, Pakistan in west, to China, Cambodia, Thailand, Vietnam and Philippines in the far-east, as well as to Sri Lanka, Nepal, Burma India and Bangladesh in the south (Pethiyagoda, 1991;Talwar and Jhingran, 1991;Conte-Grand et al., 2017). Genus Parachanna which is restricted to northeast Africa consists only of three species (Serrao 2014). The node separating the Genus Parachanna from Channa was estimated to be about 50 MYA (Benziger et al., 2011), which, corresponds to the timing of earliest Channid fossils (Archichanna and Eochanna) recorded from early Eocene by Roe (1991). Britze et al.,  (Benziger et al., 2011;Jayaram, 1999). Hora's (1949) Sathpura hypothesis on the dispersal of Malayan fauna and flora to peninsular India, proposed to explain the patterns of distribution in the Indo-Sri Lankan freshwater fishes, has suggested biogeographic links between Indian and Malayan regions, and it requires further investigation. The genus Channa is also found in both these regions, while it is interesting to note the high diversity of the genus in north-east India (Gurumayum and Tamang, 2016), which indicates a transition zone between the Indian and Malayan regions. However, the complete picture of the biogeographical affinities, dispersal & vicariance processes and speciation events within the family Channidae in the Indian sub-continent including Sri Lanka is yet to be understood.

Distribution of the family Channidae within Sri
Lanka is reviewed and presented here, for which we have examined all the available distribution records for the valid species of Sri Lankan Channids, on a template of the ichthyological zones of the island (Senanayake and Moyle, 1982). The results of this comprehensive distribution review are summarized in Figure 2, while the Supplementary Appendix 1 provides a comprehensive database of all records up to date.
In addition to the distribution data from historical field surveys on Sri Lankan freshwater fishes by Senanayake (1980) and Pethiyagoda (1991) and the most recent distribution study by De Silva et al., (2015), our compilation of Channa distribution records include other available localities of opportunistic records of such specimens by Deraniyagala (1929Deraniyagala ( , 1952, Radda (1973), Ranasinghe and Ratnayake (1992), Maduranga (2005) and Perera et al., (2014), as well as the currently available verified Channa specimens examined from the National Museum of Natural History, Colombo. Further, new localities presented in Sudasinghe et al., (2020a) have also been included in this distribution review. However, due to (a) the inability to assign historical distribution records available in above literature to one of the recently revised species of Channa marulius group (i.e. C. marulius, C. ara and C. cf. ara sensu Sudasinghe et al., 2020a) and (b) the taxonomic ambiguities in the said group, we have assigned all available distribution records for C. marulius group into a single distribution map, together with all historical distribution data for C. marulius. All distribution maps provided by Senanayake (1980), Pethiyagoda (1991), De Silva et al., (2015) and Sudasinghe et al., (2020a), were georeferenced and geographic coordinates were assigned to all distribution localities using the Calculate Geometry tool in ArcGIS 10.4.2 software by the Environmental Systems Research Institute (ESRI). Other distribution points provided in references without a map or geographic coordinates were navigated using a location search in Google Earth and indicated in maps with a different symbol indicating the uncertainty of exact locality (see Figure 2; Supplementary online appendix 1).

(e) Channa orientalis
Senanayake ( Senanayake and Moyle (1982) have identified four ichthyological zones within Sri Lanka based on the distribution patterns of freshwater fish at the level of river basins, namely the Mahaweli zone, Dry zone, Southwestern zone and a Transition zone (in between the boundary of headwater regions of the Mahaweli zone and the other three zones). Distribution data from Senanayake (1980) and Pethiyagoda (1991) have recorded Channa marulius, C. striata, C. punctata and C. kellartii (C. gachua) from the South-western, Dry as well as the Mahaweli ichthyological zones. On the other hand, according to the most recent data by De Silva et al., (2015), Channa marulius, C. orientalis and C. punctata are restricted only to the South-western Ichthyological Zone of Sri Lanka (see Figure 2). Several authors have provided evidence for population declines and local extinction of freshwater fishes of Sri Lanka (Senanayake & Moyle, 1982;Pethiyagoda 1994), but none particularly on Channids as yet. However, all aforementioned surveys have had their focus on the entire freshwater fish fauna of the island, which could have undoubtedly diluted the efforts on searching for individual species or groups in each and every major river basin.
Overlooking Channa species in such general surveys are obvious due to their nocturnal and specialist carnivore habits. Hence it is important to conduct an island wide survey particularly targeting the species in the genus Channa, representing all major river basins of the island.
Although the icthiological zones are established for Sri Lanka, those are primarily delimited based on intuitive discernment upon extensive field expertise as of many such initial works elsewhere in the world (Perera et al., 2011) and have not yet been proven through a subsequent numerical analysis (as in Perera et al., 2018), while a substantial attempt has not yet been received to predict the distribution of freshwater fish species including Channids in Sri Lanka. Therefore, it is believed that an ecological niche modeling attempt could pave the way to better understand the biogeography and distribution of Channids in the Indian sub-continent including Sri Lanka, while supporting a future numerical confirmation of the intuitively delimited ichthyological zones. Cobos et al., (2019), discussed the applicability of Maxent for ecological niche modeling and  shows the importance of Maxent as a presence-only modeling method, which follows the same approach used in traditional/intuitive ichthyological zonation in Sri Lanka, but with a rigorous processing of available data both on the species occurrence as well as predictor environmental variables. The species incidence and environmental data sets available for an ecological niche modeling exercise using Maxent to predict the possible distribution of Channiade in Sri Lanka needs to be tested for their completeness and resolution. This software uses a set of environmental grids and occurrence localities (species incidences) and the model expresses a probability distribution where each grid cell has a predicted suitability of conditions for the species (Steven et al., 2019). We argue that, although not at a fine grain of resolution, the Channid incidence data available for Sri Lanka supplemented with new findings from a rapid survey covering all major river basins of the island would yield a much better understanding to their evolution and biogeography. A reevaluation of the Ichthyological zones of Sri Lanka with results from ecological niche models would certainly shed new light to Sri Lankan freshwater biogeographical studies. Further, such complete data sets including modeled distribution would support analyses on patterns of endemism (Ramdhani et al., 2010;Perera et al., 2018;Perera et al., 2019) necessary for scientific conservation planning.

Molecular Systematics of family Channidae
Molecular Phylogenetic studies are being increasingly and rigorously used in fish taxonomy to determine the species limits and their status, describe new species, resolve taxonomic puzzles and investigate phylogenetic relationships (Benziger et al., 2011;Khare et al., 2014;Conte-Grand et al., 2017;Adamson and Britz, 2018;Sudasinghe et al., 2020a;Sudasinghe et al., 2020b). Starting with single gene sequence analysis of ribosomal DNA, mitochondrial and nuclear DNA approaches are dominated in molecular systematics today (Ward et al., 2005). DNA sequence analysis has been used for many years to assist species identifications, but different gene sequences have been used for different taxonomic groups and in different laboratories (Hebert et al., 2003). To solve these dissimilarities in molecular taxonomy and species demarcation, first, mitochondrial gene cytochrome c oxidase I (COI) was introduced for the global bio-identification system for animals which is also known as DNA barcoding and later cytochrome b (cytb) was also introduced (Hebert et al., 2003, Hellberg et al., 2014 Due to the possible presence of mobile introns and low PCR success in CO1 based barcoding in some cases, another mitochondrial DNA; NADH dehydrogenase subunit 2 (ND2), has been successfully used as a secondary or alternative barcoding gene in fish (Kocher et al., 1995, Mohapatra et al., 2018. However, nuclear genes such as the internal transcribed spacers (ITS) of rRNA genes have also been used for testing phylogeographic patterns of closely related species due to their high evolutionary rates (Presa et al., 2002).
Several studies have been conducted to investigate molecular biology and phylogeny of genus Channa during the past few decades including preliminary barcodingg studies (Serrao et. al., 2014;Conte-Grand et al., 2017). Some researches (Benziger et al., 2011;Conte-Grand et al., 2017) have studied the inter-species genetic variation of Channa, while few others (Jamaluddin et al., 2011, Bhat et al., 2014 have worked on the population genetics of the species. Phylogenetic studies have also helped resolving several taxonomic issues within the family Channidae. For example, Benziger et al., (2011) revalidated the species status of Channa diplogramma. This species was first described in 1865 from India, but remained a taxonomic puzzle until the phylogenetic study was carried out by Benziger et al., (2011). Further, DNA barcoding studies on snakeheads by Conte-Grand et al., (2017) revealed that the records of Channa orientalis from India were misidentifications, confirming the species' endemicity to Sri Lanka.
Further, previous studies have revealed the high intraspecific divergence of the several Channid species including those found in Sri Lanka; Channa striata and C. punctata (Conte-Grand et al., 2017), across the region. In a study by Abol-Munafi et al., (2007), authors analysed the partial sequences of the mitochondrial gene Cytochrome b on six Channid species; Channa marulioides, C. melasoma, C. lucius, C. gachua, C. micropeltes and C. striata to determine their phylogenetic relationships. They found that Channids are a taxonomically difficult but monophyletic group that have a single common ancestral design, but with a considerable morphological diversity. According to their study mitochondrial and ribosomal genes of Channa shows high interand intra-specific sequence variability.  Li et al., (2012) to examine the molecular phylogenetics of several Channa species.
There is no universal protocol for the number of samples of each species required for a particular molecular phylogenetic or phylogeographic study. Literature shows varied number of sampled individuals even within the same research Adamson and Britz, 2018). For example, barcoding Australian fish species project had been used one to 15 samples from each species with a mean number of 3.66 (Ward et al., 2005). Therefore, we propose at least three samples/specimens from each region or river basin or from each population belonging to a given species for a molecular biological study on the Channidae in Sri Lanka.

CONCLUSIONS AND RECOMMENDATIONS
Literature on taxonomy and biogeography of family Channidae in Sri Lanka as well as the south and soth-east Asian region indicate an incomplete knowledge including unresolved areas in species limits, their inter-and intra-specific phylogenetic relationships and the biosystematics as a whole. Taxonomy of Sri Lankan species of Channidae still depend on traditional morphology based taxonomical characterization and, have not been adequately supplemented by genetics based studies. Studies on molecular genetics, phylogenetic relationships, phylogeography and DNA barcoding of family Channidae are still in their initial stages in Sri Lanka, while being somewhat established on Indian species as well as in other regions of their range. Further, recent publications on Sri Lankan Channids (Sudasinghe et al., 2020a;Sudasinghe et al., 2020b) are filling some gaps in taxonomy and molicular systematics. Hence, the above findings integrated with ongoing baseline studies on Sri Lankan taxa is expected to shed new light on the current understanding of the family Channidae in Sri Lanka.
Due to the paucity of understanding on the origins and phylogenetic relationships among the Sri Lankan Channid species and their congeners, an initial DNA barcoding exercise to delimit species and an examination on their origins through a multilocus phylogeny is timely. Furthermore, a multiple gene based integrated molicular systematic study involving at least three specimens representing different ichthyological zones of all "putative" Channid species in Sri Lanka is an urgent requirement, which could lead to the development of a resolved phylogeny of the family Channidae. All in all, many taxonomic ambiguities within the genus Channa in Sri Lanka elaborated above demands a complete taxonomic reevaluation for the entire genus in Sri Lanka, involving a combination of morphological and molecular techniques, leading to a revision of the genus within the island.
The incompleteness of the knowledge on the distribution patterns of the Channid species in Sri Lanka, needs to be rectified based on a complete all island field survey to search for potential species of snakeheads representing all the major river basins of the island. In addition to the field surveys to document the distribution ranges, a GIS based species distribution mapping and distribution modelling study using the ecological niche modelling techniques (e.g. Maxent) is also a priority need for Channidae in Sri Lanka, so that field searches could be narrowed down and evidence-based conservation actions could be facilitated.
Snakeheads represent one of the biggest and the most exploited native freshwater species for food fish in Sri Lanka, and their use in ornamental trade is economically significant. These uncontrolled, unsustainable harvests from the wild, together with other anthropogenic pressures, would foreseeably trigger a sharp decline in snakehead populations in the country. Enhancing these stocks for extractive uses i.e. consumption and ornamental use as well as conservation, needs (a) clear identification of species and (b) a concise knowledge on their biogeographic limits. Any efforts made in this regard would be futile or even catastrophic without such knowledge as population decline and genetic degradation are imminent.