A new sciaenid fish, Johnius sasakii sp. nov. from the East Malaysian coastal waters of Sabah and Sarawak, Borneo is described herein. Johnius sasakii sp. nov. can be separated from the close congeners, Johnius heterolepis and Johnius carouna by having less gill rakers on the lower limb of the first gill arch (mode number 9 vs. 10 for J. heterolepis; 11 for J. carouna). It can be distinguished from J. heterolepis with the higher modal number of gill rakers on the upper limb of first gill arch (5 vs. 4), shorter anal-fin base length (9% vs. 10% of SL) and first anal-fin ray length (10–12% vs. 12–13% of SL) respectively. Furthermore, J. sasakii sp. nov. can be further differentiated from J. carouna by its shorter second anal-fin spine length 7–10% SL (usually 8–10%) vs. 11–14% SL (usually 11–12%) and slightly deeper body depth 25–29% SL (usually 26–28%) vs. 23–28% SL (usually 24–26%). Meanwhile, J. sasakii sp. nov. can be easily differentiated from J. macrorhynus by a present of molariform teeth on inner rows of jaws and stumpy gill rakers. Johnius (Johnius) sasakii sp. nov. can be clearly distinguished from species of the subgenus J. (Johnieops) by the lack of enlarged outer row teeth on upper jaw. A Kimura 2-parameter genetic distance comparison of 450 bp sequences of mitochondrial 16S rRNA and 488 bp nuclear gene S7 showed that J. sasakii sp. nov. are highly differentiated from J. heterolepis (16S: 10.4%, S7: 5.8%), J. carouna (16S:19.3%, S7:8.4%); and J. macrorhynus (16S: 16.7%, S7: 8.1%) respectively. The study highlights that the genetic approach from mtDNA and nDNA can contribute to the confirmation of taxonomic status of sympatric species in genus Johnius.

Given the identification of the new species Johnius taiwanesis, the Johnius genus in Taiwanese water is here reviewed through a collection of field samples, museum specimens, and a review of the Taiwanese scientific literature. Seven valid Johnius species were successfully identified and distinguished based on gill raker length, tip of upper jaw to mouth hinge length, tip of lower jaw to mouth hinge length, and length of second spine of anal fin. Our phylogenetic tree based on cytochrome oxidase subunit I (COI) showed the existence of high interspecific genetic diversity within the genus Johnius forming a monophyletic group. The Johnius species in Taiwan are mainly distributed in a latitude ranging from Xingda (22.4° N) to Hsinchu (24.8° N) with J. taiwanensis, J. distinctus, and J. belangerii representing the most abundant species caught throughout the year. Johnius amblycephalus and J. borneensis were only caught in the summer, while J. trewavasae was rarely caught. In conclusion, we provide a dichotomous key for the genus Johnius in Taiwan waters.

In terms of sheer abundance, taxonomic diversity, and species richness, Malaysia has one of the most diverse Sciaenidae in the Indo-West Pacific. Up to ten valid species of the sciaenid fish genus Johnius (e.g., J. amblycephalus (Bleeker, 1855), J. belangerii (Cuvier, 1830), J. borneensis (Bleeker, 1850), J. carouna (Cuvier, 1830), J. coitor (Hamilton, 1822), J. heterolepis Bleeker, 1873, J. macrorhynus (Lal Mohan, 1976), J. plagiostoma (Bleeker, 1849), J. sasakii Hanafi et al., 2022 and J. weberi Hardenberg, 1936), and with additional newly recorded species as J. trewavasae Sasaki, 1992, have been recorded to occur in East Malaysia (Borneo Island) coastal waters. The newly recorded species is a close congener to J. heterolepis Sasaki, 1992 and can be well distinguished by several characters and molecular evidence. The goal of this study is to review the taxonomic status of Johnius species in East Malaysia, Borneo Island, by using a literature review, morphological inference and molecular characters. Principal Component Analysis (PCA) successfully discriminates based on second anal spine length and gill raker length within sampled specimens. A phylogenetic tree based on cytochrome oxidase subunit I (COI) showed intraspecific levels of genetic differentiation within Johnius of East Malaysia, which forms a monophyletic group. Moreover, the new record of Johnius trewavasae in East Malaysia represented that the distribution of the subtropical genus Johnius extended to the southernmost part of the tropical region.

Sciaenid fishes represent a morphologically diverse and taxonomically complex family widely distributed across tropical coastal systems of the Indo-West Pacific. To investigate patterns of morphological diversification within this family, sciaenid assemblages from the east (Terengganu; South China Sea) and west (Perak; Strait of Malacca) coasts of northern Peninsular Malaysia were compared based on specimens collected between March 2015 and December 2016. Fifteen species were identified and analysed using a combination of morphometric and meristic characters. Multivariate analyses revealed pronounced morphological segregation between assemblages from the two regions. Principal Component Analysis indicated that shape variation was primarily associated with gill raker length and anal fin morphology. Species from the Terengganu assemblage were characterized by relatively longer gill rakers and shorter second anal-fin spines, whereas species from the Perak assemblage showed the opposite pattern. These contrasting morphotypes are consistent with differentiation along ecological axes related to habitat use and feeding strategies. Notably, species of the genus Johnius from the Strait of Malacca exhibited substantial morphological divergence, suggesting pronounced ecological differentiation within this genus. The observed morphological divergence between assemblages occupying contrasting coastal systems highlights the role of ecological heterogeneity in such divergence and underscores the value of ecomorphology for understanding phenotypic variation in speciose marine fish groups.

Palawan is widely recognized for its shallow-water fish biodiversity, however, the diversity of deep-sea species that inhabit its offshore waters remains poorly documented. This paper documents the first recorded presence of the Keeltail pomfret Taractes rubescens (Jordan & Evermann, 1887) in Palawan. One specimen displayed for sale was purchased on 27 April 2024 at the Puerto Princesa City New Market. According to the fish vendor, the fish was caught off the city’s eastern coastline. It weighed around 3.0 kg and measured 610 mm in total length. Other measurements included a standard length of 475 mm, a fork length of 530 mm, and a body depth of 175 mm. Additional key measurements included a 290 mm distance from snout to anal fin, a 145 mm head length, and a 175 mm pectoral fin length. Meristic features recorded include 29 dorsal fin rays, 20 anal fin rays, 42 lateral line scales, and a gill raker count of 4 + 12 gill rakers (upper limb + lower limb) on the left arch compared 3 + 14 gill rakers on the right arch. This new record adds to the growing list of deep-sea species found in the region and highlights the valuable role of local fish markets in uncovering and documenting marine biodiversity, particularly for species from less-explored deep-sea habitats.