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FAMILY Dorosomatidae Herklotsichthys quadrimaculatus (Rüppell, 1837); Native; Bluestripe Herring; Found in wetlands and river basins across the Philippines; USNM 190251; Kottelat 2013; LC Sardinella tawilis (Herre, 1927); Endemic; Freshwater, Bombon Sardinella; Endemic to Lake Taal, Luzon Island; Whitehead, 1985, Aquilino et al. 2011, Kottelat 2013; EN

FAMILY Pristigasteridae Pellona ditchela Valenciennes, 1847; Native; Indian Pellona; Found in wetlands and river basins across the Philippines; Herre 1953; LC, Published as part of Jamandre, Brian Wade, 2023, Freshwater fishes of the Philippines: a provisional checklist, pp. 151-181 in Zootaxa 5301 (2) on page 164, DOI: 10.11646/zootaxa.5301.2.1, http://zenodo.org/record/8030274, {"references":["Herre, A. W. C. T. (1953) Check list of Philippine fishes. Fish and Wildlife Service Research Report, 20, 293 - 295."]}

Jamandre, Brian Wade (2023): Freshwater fishes of the Philippines: a provisional checklist. Zootaxa 5301 (2): 151-181, DOI: 10.11646/zootaxa.5301.2.1, URL: http://dx.doi.org/10.11646/zootaxa.5301.2.1

Hata, Harutaka, Mandagi, Ixchel F., Masengi, Kawilarang W. A. (2023): Resurrection of nominal species previously regarded as junior synonyms of Thrissina baelama (Fabricius, 1775) and their re-descriptions (Teleostei: Clupeiformes: Engraulidae). Raffles Bulletin of Zoology 71: 279-302, DOI: 10.26107/RBZ-2023-0022

Chan, Jeffery C.F., Tsang, Alphonse H.F., Yau, Sze-man, Hui, Tommy C.H., Lau, Anthony, Tan, Heok Hui, Low, Bi Wei, Dudgeon, David, Liew, Jia Huan (2023): The non-native freshwater fishes of Hong Kong: diversity, distributions, and origins. Raffles Bulletin of Zoology 71: 128-168, DOI: 10.26107/RBZ-2023-0012

Coilia grayii (Richardson) Distribution. Plover Cove Reservoir (Man & Hodgkiss, 1977; Man & Hodgkiss, 1981; Lai, 2011; GBIF.org, 2021; current survey); Tai Lam Chung Reservoir (Lai, 2011; AFCD, 2021c). Native range. East and South China seas, and the Indian Ocean (East Asia). Remarks. Based on the presence of juveniles and adults, there is likely a breeding population at Plover Cove Reservoir. It was first recorded in Plover Cove Reservoir in Hong Kong in 1967 (the year the reservoir was completed) where it was suspected to originate from water piped from Shenzhen Reservoir in Guangdong (Man, 1974)., Published as part of Chan, Jeffery C. F., Tsang, Alphonse H. F., Yau, Sze-man, Hui, Tommy C. H., Lau, Anthony, Tan, Heok Hui, Low, Bi Wei, Dudgeon, David & Liew, Jia Huan, 2023, The non-native freshwater fishes of Hong Kong: diversity, distributions, and origins, pp. 128-168 in Raffles Bulletin of Zoology 71 on page 133, DOI: 10.26107/RBZ-2023-0012, http://zenodo.org/record/7815765, {"references":["Man HSH & Hodgkiss IJ (1977) Studies on the ichthyo-fauna in Plover Cove Reservoir, Hong Kong: feeding and food relations. Journal of Fish Biology, 11 (1): 1 - 13.","Man HSH & Hodgkiss IJ (1981) Hong Kong Freshwater Fishes. Urban Council Publication (Hong Kong Government), Hong Kong, 76 pp.","Lai SYH (2011) Reservoir fishes of Hong Kong with remarks on conservation options. Memoirs of the Hong Kong Natural History Society, (27): 63 - 82.","Man SH (1974) Studies on the ichthyo-fauna in Plover Cove Reservoir: with special reference to Tilapia mossambica (Peters). Unpublished PhD Thesis. University of Hong Kong, Hong Kong, pp. 1 - 8."]}

CT scans of a couple Harengula jaguana

Sardinops sp. Fig. 13G Remarks This single otolith from the Landrum Member of Texas can confidently be assigned to the recent genus Sardinops, but the single available specimen does not allow any precision at the species level. Stratigraphic and geographic distribution Bartonian: Landrum Member, Texas., Published as part of Lin, Chien-Hsiang & Nolf, Dirk, 2022, Middle and late Eocene fish otoliths from the eastern and southern USA, pp. 1-122 in European Journal of Taxonomy 814 on page 43, DOI: 10.5852/ejt.2022.814.1745, http://zenodo.org/record/6484355

Neoopisthopterus weltoni sp. nov. urn:lsid:zoobank.org:act: 023E1875-E9C9-4E5A-A087-E1F1DF4FF1C4 Fig. 13E–F Diagnosis OL/OH = 1.64–1.68, OsL/CaL = 1.00–1.07. Otoliths trapezoid, thin, with large rostrum. Sulcus wide and shallow. Ostium opens widely. Cauda straight and wide. Etymology This species is dedicated to Bruce Welton, who provided us a lot of otoliths, and as an appreciation of his extensive work on the fossil shark teeth from the Gulf Coast area. Material examined Holotype UNITED STATES OF AMERICA • Left otolith; Texas, Crockett; Landrum Member of the Cook Mountain Formation; Fig. 13E; IRSNB P 10018. Paratypes UNITED STATES OF AMERICA • 2 otoliths, of which one is figured: Fig. 13F; Texas, Stone City Bluff, Brazos River; “ Stone City beds”; IRSNB P 10019. Type locality and horizon United States of America, Crockett (Texas), Landrum Member of the Cook Mountain Formation. Dimensions of the holotype Length = 1.13 mm; height = 0.94 mm; thickness = 0.32 mm. Description This species is characterized by rectangular to trapezoid otoliths. The dorsal rim is more or less straight. The posterior rim is gently curved, forming rounded junctions with the dorsal and ventral rims. The ventral rim varies, which partly resulted from its preservation status; it is slightly irregular in the holotype (Fig. 13E), but largely undulated in the figured paratype. The anterior portion is characterized by a large, robust, and extended rostrum with a small but notable excisura. The otoliths are nearly flat on both faces. The sulcus is not deep but very wide and clearly divided into ostium and cauda. No collicula are visible. The ostial crista inferior curves somewhat upwards anteriorly and the ostium opens widely antero-dorsally. The cauda is straight and wide. At its posterior end, the cristae are indistinct. The dorsal area is somewhat hollowed out. Remarks Neoopisthopterus weltoni sp. nov. is a rare species; only three specimens are currently known: two from the Cook Mountain Formation and one from the “Stone City beds”, both in Texas. The above diagnosis allows us to assign this new species to the Recent genus Neoopisthopterus (see Nolf & Aguilera 1998: pl. 2 fig. 11 for an illustration of an otolith of the Recent N. tropicus). Stratigraphic and geographic distribution Lutetian: “Stone City beds”, Texas. Bartonian: Landrum Member, Texas., Published as part of Lin, Chien-Hsiang & Nolf, Dirk, 2022, Middle and late Eocene fish otoliths from the eastern and southern USA, pp. 1-122 in European Journal of Taxonomy 814 on pages 42-43, DOI: 10.5852/ejt.2022.814.1745, http://zenodo.org/record/6484355, {"references":["Nolf D. & Aguilera O. 1998. Fish otoliths from the Cantaure Formation (early Miocene of Venezuela). Bulletin de l'Institut royal des Sciences naturelles de Belgique, Sciences de la Terre 68: 237 - 262."]}

Clupeidae indet. Fig. 13H Remarks Clupeid otoliths are rare in the collection in terms of their numeric abundance in the associations, but they were found across different regions and ages. The mentioned specimen is an example of such a small otolith, well recognizable as a clupeid, but it does not allow a more precise assignment. Stratigraphic and geographic distribution Lutetian: “Stone City beds”, Texas; Dobys Bluff Tongue of Kosciusko Formation, Mississippi. Bartonian: Landrum Member, Texas; Cook Mountain Formation, Mississippi; “upper” Lisbon Formation, Alabama., Published as part of Lin, Chien-Hsiang & Nolf, Dirk, 2022, Middle and late Eocene fish otoliths from the eastern and southern USA, pp. 1-122 in European Journal of Taxonomy 814 on page 43, DOI: 10.5852/ejt.2022.814.1745, http://zenodo.org/record/6484355

The fossil otoliths of the southern USA have been known for more than 130 years and are among the richest assemblages worldwide. However, previous studies are often scattered and with outdated systematic scheme. A collection of over 25000 otoliths ranging in age from the Lutetian to the Priabonian from 47 sites in five states in the eastern and southern USA is analysed here. Combined with the earlier described material, at least 101 otolith-based taxa are documented, of which 83 are identified at species level. Fourteen of these are introduced as new species: Elopothrissus bernardlemorti sp. nov., “Muraenesox” barrytownensis sp. nov., Pseudophichthys texanus sp. nov., Paraconger wechesensis sp. nov., Neoopisthopterus weltoni sp. nov., “aff. Glyptophidium” stringeri sp. nov., Symmetrosulcus dockeryi sp. nov., Mene garviei sp. nov., “Citharus” varians sp. nov., Waitakia beelzebub sp. nov., Astroscopus compactus sp. nov., Parascombrops yanceyi sp. nov., Anisotremus rambo sp. nov., and Pagellus pamunkeyensis sp. nov. The assemblages are distinct fom contemporary European faunas by the complete lack of mesopelagic fish otoliths, and by the presence of sciaenids. Dominant taxa in the American Eocene are the Ophidiidae, Sciaenidae, Lactariidae, and Congridae. They indicate shallow-water environments for all the sampled sites. The notable abundance of those taxa suggests that they could have a higher turnover rate, and provided fundamental nutrition in the local Paleogene marine ecosystem. Further analyses of the species in the stratigraphic succession revealed that a faunal turnover between the Claiborne and Jackson seas was evident in teleosts, and it might be more widespread in other marine organisms in the region.

Hata, Harutaka, Koeda, Keita (2022): First Japanese Records of Sardinella albella (Teleostei: Clupeiformes: Clupeidae) from Okinawa Island, with a Key to Japanese Species of Sardinella. Species Diversity 27 (1): 37-43, DOI: 10.12782/specdiv.27.37, URL: http://dx.doi.org/10.12782/specdiv.27.37

Key to species of Sardinella recorded from Japan (Fig. 3; data of each specimen shown in Appendix 1); Japanese standard names in parenthesis 1. Pelvic fin with nine rays; lower gill rakers on first gill arch>100.............. S. aurita a (Kataboshi-iwashi) — Pelvic fin with eight rays; lower gill rakers on first gill arch, Published as part of Hata, Harutaka & Koeda, Keita, 2022, First Japanese Records of Sardinella albella (Teleostei: Clupeiformes: Clupeidae) from Okinawa Island, with a Key to Japanese Species of Sardinella, pp. 37-43 in Species Diversity 27 (1) on page 40, DOI: 10.12782/specdiv.27.37, http://zenodo.org/record/7175385

The Atlantic anchoveta, Cetengraulis edentulus (Cuvier, 1829) is one of the most commercially important fish species in the littoral of Brazil. The present study evaluates the parasitic fauna of this engraulid fish from the southeastern Brazilian coast. Between October 2019 and March 2020, a total of 100 specimens of C. edentulus from the Sepetiba Bay, Rio de Janeiro, Brazil (22°57’44”S; 43°52’28”W), were examined. Eighty-five specimens of C. edentulus were parasitized by at least one species of metazoan, with a mean of 4.32 ± 6.12 parasites/fish. Eleven species of parasites were collected: five digeneans, two monogeneans, two copepods, one isopod and one nematode. The nematode Hysterothylacium sp. was the most abundant and dominant species, representing 51.85% of the metazoan parasites collected, showing positive correlation with the host’s total length and parasite abundance and prevalence. The mean abundance and prevalence of Hysterothylacium sp. was significantly higher in female hosts. One pair of larval endoparasites showed positive covariation. Centengraulis edentulus represents a new host record for nine species of parasites. A dominance of endoparasitic larval stages is documented in the parasite community of C. edentulus. This may be a function of the feeding habits of engraulid fish, which feed mainly on zooplanktonic organisms. It may also have to do with to the fact that C. edentulus is the intermediate and/or paratenic host of fish parasites, birds, and marine mammals.

Lycengraulis grossidens (Spix & Agassiz, 1829). Atlantic Sabretooth Anchovy; Anchoa Dentada, Anchoa Dentona. Distribution: Global: Western Atlantic Ocean; from northern Belize to northern Brazil entering estuaries and littoral lagoons and ascending river courses; Costa Rica: To (Atlantic), 0��� 3 m.a.s.l., Per, Dia. Occurrence and conservation status: Nat, LC. References: Bussing (1998: 122; brief description, including illustrations and an identification key, information on distribution, with a map, and ecology), Angulo et al. (2013: 990; listed, including taxonomic information and distributional data) and Robertson & Van Tassell (2019: 2963; detailed description, including illustrations, information on distribution, with a map, and ecology)., Published as part of Angulo, Arturo, 2021, New records and range extensions to the Costa Rican freshwater fish fauna, with an updated checklist, pp. 1-72 in Zootaxa 5083 (1) on page 23, DOI: 10.11646/zootaxa.5083.1.1, http://zenodo.org/record/5800630, {"references":["Bussing, W. A. (1998). Freshwater fishes of Costa Rica. Editorial Universidad de Costa Rica, San Jose, Costa Rica, 468 pp.","Robertson, D. R. & Van Tassell, J. (2019) Shorefishes of the Greater Caribbean: online information system. Version 2.0 Smithsonian Tropical Research Institute, Balboa, Panama. Available from: https: // biogeodb. stri. si. edu / caribbean / en / pages (accessed 27 August 2021)."]}

Anchoa curta (Jordan & Gilbert, 1882). Short Anchovy; Anchoa Corta. Distribution: Global: Eastern Pacific Ocean; from central Baja California, Mexico, to northern Peru; entering estuaries and littoral lagoons and ascending river courses; Costa Rica: Tr (Pacific), 0��� 12 m.a.s.l., Per, Dia. Occurrence and conservation status: Nat, LC. References: Bussing & L��pez (1994: 50; brief description, including an illustration), Angulo et al. (2013: 990; listed, including taxonomic information and distributional data) and Robertson & Allen (2015: 480; detailed description, including illustrations, information on distribution, with a map, and ecology)., Published as part of Angulo, Arturo, 2021, New records and range extensions to the Costa Rican freshwater fish fauna, with an updated checklist, pp. 1-72 in Zootaxa 5083 (1) on page 22, DOI: 10.11646/zootaxa.5083.1.1, http://zenodo.org/record/5800630, {"references":["Robertson, D. R. & Allen, G. R. (2015) Shorefishes of the Tropical Eastern Pacific: online information system. Version 2.0. Smithsonian Tropical Research Institute, Balboa, Panama. Available from: https: // biogeodb. stri. si. edu / sftep / en / pages (accessed 27 August 2021)."]}

Anchoviella elongata (Meek & Hildebrand, 1923). Elongate Anchovy; Anchoveta Alargada. Distribution: Global: Western Atlantic Ocean; from northern Belize to northern Colombia; entering estuaries and littoral lagoons and ascending river courses; Costa Rica: To and Pa (Atlantic), 0��� 5 m.a.s.l., Per, Dia. Occurrence and conservation status: Nat, LC. References: Angulo et al. (2013: 990; listed, including taxonomic information and distributional data) and Robertson & Van Tassell (2019: 2957; detailed description, including illustrations, information on distribution, with a map, and ecology)., Published as part of Angulo, Arturo, 2021, New records and range extensions to the Costa Rican freshwater fish fauna, with an updated checklist, pp. 1-72 in Zootaxa 5083 (1) on page 23, DOI: 10.11646/zootaxa.5083.1.1, http://zenodo.org/record/5800630, {"references":["Robertson, D. R. & Van Tassell, J. (2019) Shorefishes of the Greater Caribbean: online information system. Version 2.0 Smithsonian Tropical Research Institute, Balboa, Panama. Available from: https: // biogeodb. stri. si. edu / caribbean / en / pages (accessed 27 August 2021)."]}

Family Engraulidae Gill, 1861. Anchovies; Boquerones, Anchovetas, Anchoas. 3 G, 6 S., Published as part of Angulo, Arturo, 2021, New records and range extensions to the Costa Rican freshwater fish fauna, with an updated checklist, pp. 1-72 in Zootaxa 5083 (1) on page 22, DOI: 10.11646/zootaxa.5083.1.1, http://zenodo.org/record/5800630

Family Clupeidae Cuvier, 1816. Thread-Herrings, Shads, Sardines, Piquitingas, Pilchards, Menhadens, Herrings; Sardinetas, Piquitingas, Machuelos, Arenques, Sardinas. 4 G, 5 S., Published as part of Angulo, Arturo, 2021, New records and range extensions to the Costa Rican freshwater fish fauna, with an updated checklist, pp. 1-72 in Zootaxa 5083 (1) on page 22, DOI: 10.11646/zootaxa.5083.1.1, http://zenodo.org/record/5800630

The knowledge of the Costa Rican freshwater fish fauna continues to grow given the discovery of new taxa, the recognition of taxa resurrected from synonymy and the corroboration of new country records and new range extensions. Moreover, recent advances in the understanding of the phylogenetic relationships and status of many supraspecific groups have led to numerous taxonomic and nomenclatural changes. Given this, the purpose of this paper is to update the known composition, distribution and clasification of the Costa Rican freshwater fish fauna taking as reference the most recent list for the country published by Angulo et al. (2013). A total of 23 new country records (i.e., species; distributed in 17 families and 21 genera), 33 new range extensions (distributed in 20 families and 30 genera) and several nomenclatural changes are reported, illustrated and discussed here. An updated and annotated checklist of the freshwater fishes of the country (including data for a total of 283 species, 13 of which are exotic, distributed in two classes, 27 orders, 55 families and 136 genera) is also provided.

Lile piquitinga (Schreiner & Miranda Ribeiro, 1903). Atlantic Piquitinga; Sardineta Piquitinga, Piquitinga. Distribution: Global: Western Atlantic Ocean; from eastern Costa Rica to southern Brazil; entering estuaries and littoral lagoons and ascending river courses; Costa Rica: Si (Atlantic), 0��� 66 m.a.s.l., Per, Dia. Occurrence and conservation status: Nat, LC. References: Angulo et al. (2013: 990; listed, including taxonomic information and distributional data) and Robertson & Van Tassell (2019: 2927; detailed description, including illustrations, information on distribution, with a map, and ecology)., Published as part of Angulo, Arturo, 2021, New records and range extensions to the Costa Rican freshwater fish fauna, with an updated checklist, pp. 1-72 in Zootaxa 5083 (1) on page 22, DOI: 10.11646/zootaxa.5083.1.1, http://zenodo.org/record/5800630, {"references":["Robertson, D. R. & Van Tassell, J. (2019) Shorefishes of the Greater Caribbean: online information system. Version 2.0 Smithsonian Tropical Research Institute, Balboa, Panama. Available from: https: // biogeodb. stri. si. edu / caribbean / en / pages (accessed 27 August 2021)."]}

Dorosoma chavesi Meek, 1907. Nicaragua Gizzard Shad; Sardina, Sardinilla, Sabalete, Sardina de R��o. Distribution: Global: Middle America; from western Nicaragua (lakes Xolotl��n and Cocibolca and affluent streams or rivers) to northern Costa Rica, Atlantic drainages; Costa Rica: LN, RF, SJ, SC, Sa and To (Atlantic), 0��� 50 m.a.s.l., Per, Dia. Occurrence and conservation status: Nat, NT. References: Bussing (1987: 65; 1998: 68; brief description, including illustrations and an identification key, information on distribution, with a map, and ecology) and Angulo et al. (2013: 990; listed, including taxonomic information and distributional data)., Published as part of Angulo, Arturo, 2021, New records and range extensions to the Costa Rican freshwater fish fauna, with an updated checklist, pp. 1-72 in Zootaxa 5083 (1) on page 22, DOI: 10.11646/zootaxa.5083.1.1, http://zenodo.org/record/5800630

Lile stolifera (Jordan & Gilbert, 1882). Pacific Piquitinga, Striped Herring; Piquitinga Pelada, Sardinita Rayada, Sardina Rayada, Sardineta. Distribution: Global: Eastern Pacific Ocean; from southern Baja California Sur, Mexico, to northern Peru; entering estuaries and littoral lagoons and ascending river courses; Costa Rica: Tr (Pacific), 0��� 10 m.a.s.l., Per, Dia. Occurrence and conservation status: Nat, LC. References: Bussing & L��pez (1994: 46; brief description, including an illustration), Angulo et al. (2013: 990; listed, including taxonomic information and distributional data) and Robertson & Allen (2015: 537; detailed description, including illustrations, information on distribution, with a map, and ecology)., Published as part of Angulo, Arturo, 2021, New records and range extensions to the Costa Rican freshwater fish fauna, with an updated checklist, pp. 1-72 in Zootaxa 5083 (1) on page 22, DOI: 10.11646/zootaxa.5083.1.1, http://zenodo.org/record/5800630, {"references":["Robertson, D. R. & Allen, G. R. (2015) Shorefishes of the Tropical Eastern Pacific: online information system. Version 2.0. Smithsonian Tropical Research Institute, Balboa, Panama. Available from: https: // biogeodb. stri. si. edu / sftep / en / pages (accessed 27 August 2021)."]}

Sardinella aurita Valenciennes, 1847. Round Sardinella, Spanish Sardine; Alacha, Sardina Espa��ola. Distribution: Global: Atlantic Ocean; from Cape Cod, USA, to northern Argentina in the western Atlantic and from southern Espa��a to South Africa in the eastern Atlantic; entering estuaries and littoral lagoons and ascending river courses; Costa Rica: To (Atlantic), 0��� 3 m.a.s.l., Per, Dia. Occurrence and conservation status: Nat, LC. References: Angulo et al. (2013: 990, as Sardinella brasiliensis (Steindachner 1879) ���missidentification; listed, including taxonomic information and distributional data) and Robertson & Van Tassell (2019: 2939; detailed description, including illustrations, information on distribution, with a map, and ecology)., Published as part of Angulo, Arturo, 2021, New records and range extensions to the Costa Rican freshwater fish fauna, with an updated checklist, pp. 1-72 in Zootaxa 5083 (1) on page 22, DOI: 10.11646/zootaxa.5083.1.1, http://zenodo.org/record/5800630, {"references":["Robertson, D. R. & Van Tassell, J. (2019) Shorefishes of the Greater Caribbean: online information system. Version 2.0 Smithsonian Tropical Research Institute, Balboa, Panama. Available from: https: // biogeodb. stri. si. edu / caribbean / en / pages (accessed 27 August 2021)."]}

Anchoa lucida (Jordan & Gilbert, 1882). Bright Anchovy; Anchoa Bocona, Anchoa Ojitos. Distribution: Global: Eastern Pacific Ocean; from central Baja California, Mexico, to northern Peru; entering estuaries and littoral lagoons and ascending river courses; Costa Rica: Ba (Pacific), 0��� 32 m.a.s.l., Per, Dia. Occurrence and conservation status: Nat, LC. References: Bussing & L��pez (1994: 50; brief description, including an illustration), Angulo et al. (2013: 990; listed, including taxonomic information and distributional data) and Robertson & Allen (2015: 486; detailed description, including illustrations, information on distribution, with a map, and ecology)., Published as part of Angulo, Arturo, 2021, New records and range extensions to the Costa Rican freshwater fish fauna, with an updated checklist, pp. 1-72 in Zootaxa 5083 (1) on page 23, DOI: 10.11646/zootaxa.5083.1.1, http://zenodo.org/record/5800630, {"references":["Robertson, D. R. & Allen, G. R. (2015) Shorefishes of the Tropical Eastern Pacific: online information system. Version 2.0. Smithsonian Tropical Research Institute, Balboa, Panama. Available from: https: // biogeodb. stri. si. edu / sftep / en / pages (accessed 27 August 2021)."]}

Fish retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) are critical RNA sensors in cytoplasm and are involved in antiviral innate immunity. However, some species of fish lack RIG-I gene, and the function of RLR members in RIG-I-absent fish is poorly understood. In the present study, MDA5, LGP2 and MAVS genes were identified in commercially important snakehead Channa argus. But, RIG-I gene was not found in this fish, and a systematic analysis of RLRs in available genome database of fish indicated the absence of RIG-I in the Acanthomorphata, Clupeiformes and Polypteriformes, suggesting that loss events of RIG-I gene may have occurred independently three times in the evolutionary history of fish. The MDA5, LGP2 and MAVS in snakehead have conserved protein domains and genomic location based on sequence, phylogenetic and syntenic analyses. These genes are constitutively expressed in healthy fish and can be induced by polyinosinic and polycytidylic acid (poly(I:C)) stimulation in vitro. It is further revealed that the snakehead MDA5 and LGP2 have binding capacity with dsRNA, such as poly(I:C), and MDA5 can interact with MAVS, implying the antiviral function of MDA5 in the RIG-I-absent fish.