Johnius trewavasae Sasaki 1992
Creators: name: Hanafi, Norhafiz
name: Chen, Meng-Hsien
name: Chang, Chih-Wei
name: Chao, Ning Labbish
name: Seah, Ying Giat
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Perciformes
Sciaenidae
Johnius
Johnius trewavasae

description: Johnius trewavasae Sasaki, 1992
(Common name: Trewavas croaker)
(Fig. 15–16, Table 8–9)
Johnius trewavasae Sasaki, 1992: 191 (type locality: Taiwan Strait. Holotype: HUMZ 109504. Paratypes: ANSP 52863 (1), 53478 (2); CAS-SU 60859 (1), 60870 (1), 60918 (1), 61045 (3, 2 c&s), 61080 (2), 61484 (2); HUMZ 109501 (1). Johnius trewavasae Sasaki, 1992: Sasaki, 2000: 621; Sasaki, 2001: 3152; Ng et al., 2015: 327.
Material examined. Non-types: NMMB-P15218 (5, 117.11 to 141.73 mm SL), Guangdong, China, 1 June 2010; NMMB-P37087 (4, 110.49 to 136.29 mm SL), Sarikei, Sarawak, Malaysia, 14 March 2017; NMMB-P23653 (3, 129.67 to 133.81 mm SL), Tanjung Gemok, Pahang, Malaysia, 10 June 2014.
Diagnosis. A species of Johnius with the following combination of characters: snout steep, obtusely rounded; chin lacking barbel; scales above lateral line 4 to 6, below lateral line 7 to 10; gill rakers very short, obtuse, gill rakers at lower limb 8 to 10; second anal spine length 25 to 37% HL; scales ctenoid on body, large, and easily fallout.
Description. Counts and measurements of the type specimens are shown in Table 8. The following data is provided for the Sasaki (1992) measurement first as comparison, followed by the size range and mean for the 4 voucher specimens.
Small species with a moderately elongated body; body depth 25 to 29% of standard length. Eye moderately large, 18 to 24% of head length. Interorbital width 23 to 27% of head length. Snout steep, obtusely rounded, projecting slightly in front of upper jaw; mouth small, inferior; upper jaw extending backward below front margin of pupil; no barbel on chin; teeth differentiated into large and small in upper jaw only, the large ones close-set, not canine like, forming outer series; lower jaw with a band of villiform teeth. Gill rakers short, obtuse, about 1/5 length of gill filaments at angle of arch, 6 to 8 on lower limb of first gill arch. Dorsal fin with X to XI (most frequently X) spines, followed by a notch, second part of fin with I spine and 26 to 31 soft rays; anal fin with II spines and 7 or 8 (most frequently 7) soft rays, second spine rather short, slender, 25 to 35% of head length; caudal fin rhomboidal. Scales large, those on flanks much larger than those on the lateral line, 4 or 6 scale rows above lateral line to origin of dorsal fin, 6 to 14 scale rows below lateral line to origin of anal fin; scales cycloid (smooth) on head and throat, ctenoid (rough to the touch) on other parts of head and body; small scales present on soft parts of dorsal and anal fins; lateral line scales reaching tip of caudal fin. Swimbladder hammer-shaped, with about 14 pairs of arborescent appendages along its sides, the first pair entering head beyond transverse septum and sending a palmate branch to front of the pectoral arch. Sagitta with a tadpole-shaped impression, with long axis of its head lying obliquely to that of the sagitta and tail expanded and deepened as hollow cone connected with the head by a narrow groove.
Distribution. Singapore, north of Taiwan, Hong Kong, and Shanghai.
Remarks. Among the Johnius (Johnius) species with pointed snout and large ctenoid scales (4–6 scales above lateral line), J. trewavasae can be mainly differentiated from J. macrorhynus and J. heterolepis by the lower number of gills raker count on the lower limb (obtuse, short, 8–10 in trewavasae vs. stumpy, short, 7–8 in macrorhynus vs. slender, short, 9–11 in heterolepis) and a shorter lower jaw (33.8–38.4% HL in trewavasae vs. 33.8–38.4% HL in macrorhynus vs. 40.3–44.2% HL in heterolepis). Meanwhile, main criteria of J. macrorhynus can be distinguished by J. trewavasae by the presence of an inner, short row of molariform teeth at posteriorly. In addition, J. trewavasae can be easily differs from J. carouna and J. sasakii in having the slender and rather short second anal spine fin length (24–37% of HL in trewavasae vs. stiff, long, 32–49% of HL in carouna vs. stiff, short, 25–35% of HL in sasakii) respectively.
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According to Ng et al., (2015) and Sasaki (2000), both references mentioned J. trewavasae has been recorded occurring in Malaysia waters. Moreover, this species was synonym and frequently misapplied name as J. heterolepis and J. macrorhynus in Malaysian waters. Indicates from the Fig. 16 shown the new extension of record sites in the East Malaysia waters, concisely at the Sarikei, Sarawak states. According to Ng et al., (2015) and Sasaki (2001) previous collection discovered J. trewavasae (LSUMZ 16645) occurring in the Eastern Johor Strait, Malaysia or Singapore waters. Thus, the extension distribution evidence discovered from this study shown several population of J. trewavasae might be has been established in the Malaysian waters.
Molecular verification. This work produced phylogenetic tree sequences utilising COI genetic markers with congener Johnius species in East Malaysian seas and demarcated them with GenBank sequences to clarify the taxonomic status of J. trewavasae with congener species (Lo et al., 2017), as shown in Fig. 17. Johnius trewavasae was a sister clade to J. sasakii and a sister group to J. heterolepis and J. carouna, according to the phylogenetic tree connection (Fig. 17). Meanwhile, Dendrophysa russelii is the outgroup clade, with a strong bootstrap value confirming the connection and validation species, while J. amblycephalus is the basal clade. According to pairwise K2P genetic distances (Table 9), J. trewavasae is 16% distinct from J. sasakii, 16% different from J. carouna, 15% different from J. heterolepis, 36% different from J. amblycephalus, and 36% different from the outgroup D. russelii. In conclusions, the Johnius species in this section formed a monophyletic clade, which integrated with complementary approach supported by morphological and genetic evidence confirming the J. trewavasae status.
description: Published as part of Hanafi, Norhafiz, Chen, Meng-Hsien, Chang, Chih-Wei, Chao, Ning Labbish & Seah, Ying Giat, 2024, Taxonomic review of the genus Johnius (Perciformes: Sciaenidae) from East Malaysian waters, with comments on newly recorded Johnius species, pp. 85-117 in Zootaxa 5550 (1) on pages 108-112, DOI: 10.11646/zootaxa.5550.1.11, http://zenodo.org/record/14388193