Niwaellatigrina, Zhang, Hai-Xin, Zhang, Yan-Ping, Chen, Wen-Jing & Zhang, E., 2025

3.1 Niwaellatigrina sp. nov.

( Fig. 2 View FIGURE 2 )

Holotype. JPIFS20230401 , 55.7mm SL, from Ding-Jiang flowing into Xiu-Shui in Tonggu County (28°30′55″N, 114°16′59″E), Jiangxi Province; collected by Hai-Xin Zhang, in April 2023. GoogleMaps

Paratypes. IHB 20230402 , 59.5 mm SL, other data same as holotype; GoogleMaps JPIFS 20230803 -20, 18 specimens, 46.8–63.9mm SL, from Jinsha-He draining into Xiu-Shui in Tonggu County (28°44′1″N, 114°13′7″E), Jiangxi Province, China; collected by Hai-Xin Zhang, in April 2023. GoogleMaps

Diagnosis. Niwaella tigrina is distinguished from all Chinese congeneric species by its unique body coloration featuring 20–25 transverse black bars on the dorsum and upper portion of the flank and an indistinct blackish mid-dorsal stripe from the nape to the caudal-fin (vs. a row of transverse black blotches on the dorsum and vermicular black marks on the upper portion of the flank, or a conspicuous dark brown mid-dorsal stripe and numerous vermicular marks on the dorsum and upper portion of the flank). It is similar to N. xingjiangensis and N. brevipinna in possessing a lower jaw fully covered by the lower lip, a trait not shared with other congeneric species. Niwaella tigrina is further distinguished from N. xingjiangensis by having 17–20 brownish or black vertical bars below the mid-lateral line of the body (vs. 16–18, with a few anterior bars fused to form a dark stripe along the mid-lateral line). Additionally it has a thicker (vs. slender) curved suborbital spine with a shorter (vs. longer) processus latero-caudalis, which is less than one-fifth (vs. one-third) of the processus medio-caudalis. Furthermore, it differs from N. brevipinna in having five (vs. six) and six (vs. four) branched dorsal- and anal-fin rays, respectively.

Description. Morphometric measurements for type specimens were provided in Table 2. General body appearance and structures of different mouthpart depicted in Fig. 2 View FIGURE 2 and Fig. 3a View FIGURE 3 , respectively. The body is moderately small, slender, and slightly compressed laterally; depth is nearly uniform anterior to anal-fin origin, slightly decreasing towards caudal-fin base.

The head is relatively shorter but longer than the maximum vertical depth of the body. The snout looks slightly obtuse in lateral view and triangular or bluntly pointed in dorsal and ventral view, almost equal to postorbital head length. The eyes are small, positioned dorso-laterally in the middle of the head, with convex and narrow interorbital space; diameter nearly equal to interorbital width. The mouth is small and inferior, with three pairs of short barbels: one pair of rostral barbels not reaching the corners of the mouth, one pair of maxillary barbels not reaching the anterior margin of the eye, and one pair of maxillomandibular barbels. The lips are fleshy and smooth. The upper lip is broadened and continuous with a thick lower lip. The lower lip is divided into two well-developed mental lobes ( Fig. 2a View FIGURE 2 ; Fig. 3a View FIGURE 3 ). The lower jaw is fully covered by the lower lip. The subocular spine is thick and curved, with processus latero-caudalis being shorter than one-fifth of its processus medio-caudalis ( Fig.4b View FIGURE 4 ). The lateral line is short, not reaching to the tip of the pectoral fin ( Fig. 2a View FIGURE 2 ). Body covered with fine and rounded scales. Each scale has a large focal area, with 23–26 primary radial grooves and a few secondary radial grooves ( Fig.3b View FIGURE 3 ). The vertebrae arrangement is 4+41+1 ( Table 2).

The dorsal fin contains three unbranched and five branched rays, making it moderately short. The distal margin is slightly concave, inserted just behind the midpoint between the tip of the snout and the caudal-fin base, or opposite to pelvic-fin insertion. The pectoral fins are with one unbranched and six or seven branched rays, extending from the posterior margins of the gill cover and stretched backward around one-third distance from the pectoral to the pelvic-fin base. The pelvic fins are with one unbranched and six branched rays. These are closer to the caudal fin than to the pelvic fin insertion and extended slightly beyond the vertical line at the posterior end of the dorsal fin but do not reach one-third of the distance to the origin of the anal fin. The anal fin contains three unbranched and branched rays, originating closer to the caudal-fin base than to the pelvic-fin insertion and extending to backward direction about to one-half distance to the caudal-fin base. Finally, the caudal fin is truncated or slightly notched at the tip ( Fig. 2 View FIGURE 2 ).

Coloration. The formalin-preserved specimens are yellowish on the dorsal surface of the body, while lighter ventrally. The top of the head, opercle, and sub-opercle are grayish, with a touch of grayish-yellow, all sparsely scattered with black spots. The ventral side of the head is grayish-white. A black stripe extends from the nape, through the eye, to the insertion of the first rostral barbel. An indistinct blackish band advances from the posterior margin of the head to the caudal-fin base. Additionally, the dorsum and upper portion of the flank possess 20–25 transverse brown bars creating a tiger-striped pattern. Most of these brown bars extended downwards beyond a faint blackish band located just above the mid-lateral line of the body, reaching into the lower portion of the flank. However, the bars did not stretch to the ventral surface of the body. The dorsal fin exhibits two or three striations characterized by black spotting. The caudal fin has two or three striations running across the fin rays with distinct dark black spots on the upper portion of the caudal-fin base. A few blackish flecks are present on the distal portion of the pectoral fins, the proximal portion of the pelvic fins, and the basal portion, as well as on several leading rays of the anal fin.

Sexual dimorphism. No obvious signs of sexual dimorphism appeared in the external morphology.

Distribution and habitat. Niwaella tigrina has been observed from Ding-Jiang and Jinsha-He, both flowing into Xiu-Shui, an affluent of Lake Poyang in Jiangxi Province of East China ( Fig. 1 View FIGURE 1 ). It prefers streams with clean water, strong currents, and gravelly bottoms as habitat.

Etymology. The epithet, used as an adjective, is derived from the Latin word tigrinus (= tiger-striped), referring to the presence of tiger stripes on the dorsum and upper part of the flank. The Chinese name here suggested for this new species is“ njử后ǾAEƟ ”.

3.2 Sequence variation and molecular phylogeny

A total length of 1, 023 bp was retained after trimming and used as subsequent alignment. This included 1020 conserved sites, three variable sites, zero parsimony in formative sites, and three singleton sites. The mean nucleotide frequencies of the described species were: A=26.3%, T=32.6%, C=26.4%, and G=14.8%, with an A-T rich base composition of 58.8%.

The phylogenetic tree constructed using the Cyt b gene for all the analyzed Niwaella species is presented in Fig. 5 View FIGURE 5 , based on ML methods. In the topology of these trees, six samples of the newly described species exclusively clustered into a single lineage. These samples were closely related to those of other Chinese Niwaella species, which collectively formed a well-defined clade.