Pleuronectiformes Bleeker 1859
Creators: name: Pillai, Honey Unnikrishna
name: Dutta, Sayani
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Actinopterygii

description: Results and Discussion
The term “flatfish” was first introduced by Willughby in 1686 in his work L’Historia Piscium (Willughby, 1686). Artedi (1792) reported the occurrence of one flatfish genus, namely, Pleuronectes and included all the flatfishes under that genus. Later, Lacepede (1801) subdivided the genus Pleuronectes into four subgenera and recorded 29 species of flatfish without assigning any particular name to them. Dumeril (1806) updated the taxonomic status of flatfishes to the family level, followed by the work of Quensel (1806), who divided flatfishes into two genera - Pleuronectes and Solea. Muller (1846) provided the name of a new order named Anacanthinii, which included Pleuronectoids, Gadoids and Ophidoids. Cantor (1849) included flatfishes under the family Pleuronectidae within the order Anacanthinii. Kyle (1900) divided the order Heterosomata into two families namely Pleuronectidae and Soleidae, which were further divided into seven sub-families. Nelson et al. (2016) recognized 772 valid species under 14 families of flatfish in the order Pleuronectiformes. According to Fricke et al. (2024), a total of 815 species represented by 124 genera and 14 families of flatfish have been found distributed across the world oceans.
Based on the literature review conducted within India, this study documented 108 flatfish species from 35 genera across 10 families, out of the global count of 815 species spanning 124 genera and 14 families. The most prevalent families globally and in India are Soleidae, Bothidae, and Cynoglossidae (refer to Table 1). Comparative analysis of valid flatfish genera and species globally versus in India has revealed that about 13% of the globally reported species have been recorded from India. Across the four studied biogeographic regions in India —namely, the Arabian Sea, Bay of Bengal, Andaman and Nicobar regions, and Lakshadweep waters—the dominant families identified were Cynoglossidae, Bothidae, Soleidae, and Paralichthyidae. The family Psettodidae was consistently present across all regions, while others such as Citharidae, Pleuronectidae, Samaridae, Poecilopsettidae, and Paralichthodidae exhibited minimal and scattered distributions (see Table 2).
The Bay of Bengal recorded the highest number of species, followed by the Arabian Sea, Andaman and Nicobar regions, and Lakshadweep waters. Four species were ubiquitously found across all locations. However, 11 species were exclusive to the Arabian Sea and 20 to the Bay of Bengal. Additionally, six species were uniquely reported from the Andaman and Nicobar regions and two from Lakshadweep. In terms of conservation status according to the IUCN, approximately 71 species were categorized as “Least Concern”, 34 as “Data Deficient”, two species— Cynoglossus macrostomus (Norman) and Glyptocephalus cynoglossus (Linnaeus) —as “Vulnerable”, and one species, Paralichthys lethostigma (Jordan & Gilbert), as “Near Threatened”. The IUCN status of Paraplagusia blochii (Bleeker) remains unassessed (Table 3).
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Note: DD—Data Deficient; LC—Least Concern; NT—Near Threatened; VU—Vulnerable; NE—Not Evaluated; NA— Not Applicable, +— present; - — absent
The impetus for assembling this comprehensive document on flatfishes from India stems from the critical ecological and economic roles these species play. Flatfishes are integral to the benthic ecosystem, providing essential services that sustain environmental balance (Link et al. 2021). They are vital components of commercial, recreational, and artisanal fisheries around the world (Astarloa et al. 2002; Nair 2011; Nair and Gopalakrishnan 2014). However, intensified fishing practices such as trawling and dredging have disrupted seabed ecosystems and altered the habitats of benthic organisms on a global scale. These activities have significantly affected flatfish populations, influencing their distribution, survivability, and dietary patterns due to their close association with benthic environments (Auster and Langton 1999). In India, overfishing and intensive trawling activities are major disturbances to the seabed, negatively impacting benthic communities, including flatfish populations. This persistent disruption compromises the health and stability of these ecosystems, as highlighted in several studies (Thomas 2016; Das 2018; Sahayaraju and Jamet 2021; Dasmahapatra 2023).
When comparing different geographical zones, it was evident that the Bay of Bengal region reported a higher number of flat fish species (84) compared to other zones such as the Arabian Sea (69), Andaman and Nicobar regions (36), and Lakshadweep waters (12). Madhupratap et al. 2001 reported that among the northeastern and southeastern regions of Arabian Sea along the west coast of India, the northern zone is dominated by carnivorous fishes, whereas the southern zone sustains more planktivorous fishes. Similarly in a recent study (Vijith et al. 2023), which assessed the geographical distribution of carnivorous and planktivorous fishes in the western Bay of Bengal showed that the southwestern Bay of Bengal was rich in fisheries and more planktivorous compared to the northwestern Bay of Bengal, which was more carnivorous. Additionally, global studies (Amezcua et al. 2003; Statkus 2006; Raedemaecker et al. 2012; Spinner et al. 2016) showed that flatfishes tend to prefer muddy and sandy bottoms, specific sediment nature, grain size, and food type. The unique geographic features of the Bay of Bengal, with significant input of organic silt from major riverine systems and the presence of extensive deltaic coverage, dunes, and mudflats (Das 2018), could be the important factors for the greater diversity of flatfish in this area.
One of the most discussed species under the “Data Deficient” category from India is Psettodes erumei (Bloch), which has been reported as heavily exploited within the fishing zones of the tropical waters. Nair and Gopalakrishnan (2014) reported that the landings of this species drastically decreased in India during the period 2005 to 2012. The biology and fishery of Psettodes erumei in India were addressed by Pradhan (1962) and Devadoss et al. (1977). Also, the dimorphic forms of Psettodes erumei were observed by Das and Mishra (1989a and b).
Two species Cynoglossus macrostomus and Glyptocephalus cynoglossus, were categorized as “Vulnerable” in IUCN status. Cynoglossus macrostomus is one of the most common and commercially important flatfish species available in India (Manojkumar 2006), and the present study noted its distributional records in both Bay of Bengal and Arabian Sea (Barman et al. 2007a and b; Thomas et al. 2016; Mogalekar et al. 2018). Additionally, several studies (Khan and Nandakumaran 1993; Jayaprakash 1998; Jayaprakash 1999; Jayaprakash 2000; Jayaprakash 2001; Manojkumar 2006; Nair 2007) on the population dynamics, stock assessment, fishery and biology of this particular species were conducted along the west coast of India. It was noted that the other species Glyptocephalus cynoglossus had a limited spatial distribution in Indian waters, found to be recorded only from the southern region of the Bay of Bengal (Mogalekar et al. 2018). Paralichthys lethostigma, which was listed as ‘‘Near Threatened’’ is a recently recorded species from Andhra Pradesh (Venkatrayulu and Venkateswarlu 2023).
description: Published as part of Pillai, Honey Unnikrishna & Dutta, Sayani, 2024, A Review of Flatfish (Order: Pleuronectiformes) Diversity in Indian Waters: A Literature Overview, pp. 337-353 in Zootaxa 5523 (3) on pages 338-347, DOI: 10.11646/zootaxa.5523.3.2, http://zenodo.org/record/13949443