The mitre squid Uroteuthis chinensis is distributed widely in the Chinese coastal areas and contributes to the majority of the Chinese neritic squid fishery, especially in the South China Sea. However, little has been investigated about its life history traits, despite its commercial importance. In this study, using samples of U. chinensis collected through bottom trawlers from December 2019 to March 2021 in the northwestern South China Sea, biological traits including hatching date, growth pattern and dorsal mantle length at maturity of male individuals were explored by age determination based on statolith microstructure analysis. The results indicated that the U. chinensis showed a year-round spawning pattern with three main cohorts (spring, summer and autumn) that can be identified according to their hatching season. The range of the dorsal mantle length (DML) was 117–259 mm for females and 70–312 for males, and the body weight ranged from 55.1 to 480.5 g for females and from 19.3 to 560.2 g for males; the age ranges were estimated between 82 and 173 days for females and between 76 and 175 days for males. As for the length–weight relationship, males possessed a larger mantle length than females, while the body weight of females increased more compared to males at the same mantle length. The population recruits to the fishing ground, with individuals reaching sexual maturity at around 3 months, and the lifespan is less than 200 days. The growth model is well described by the exponential equation, which revealed that spring and autumn cohorts showed a higher growth rate than summer cohorts. As for male individuals, the smallest dorsal mantle length at maturity (DML_50%) was recorded in the spring cohort (DML_50% = 116 mm) compared with the summer (DML_50% = 129 mm) and autumn cohorts (DML_50% = 149 mm). This study provides key and updated fishery biological information of U. chinensis in the South China Sea and contributes to the understanding of U. chinensis resources.

The population genetic structure of 211 samples of Loliolus (Nipponololigo) beka, which were selected from across seven geographic localities—in the Bohai Sea, the Yellow Sea and the East China Sea—were analyzed using mitochondrial COI and 16S rRNA gene markers. Phylogenetic trees and a haplotype network both showed that the L. (N.) beka localities were genetically distinct, forming two homogeneous lineages: Lineage A and Lineage B. The results of an AMOVA showed that the genetic variation in the L. (N.) beka populations was dominated by the genetic variation between the two lineages, and both the genetic distance and genetic differentiation indices indicated that the genetic differentiation between the two lineages of L. (N.) beka in Chinese waters had reached the level of species divergence. To further confirm the differences between the two lineages shown in the molecular results, we performed a detailed analysis based on morphometric observations and a multivariate statistical analysis to compare the morphology characteristics of Lineage A and Lineage B. The results showed that there were significant differences (p < 0.05) in the ventral mantle length (VML); the mantle width index (MWI); the fin width index (FWI); the head length index (HLI); the left Arm IV length index (LALI4), the right Arm III length index (RALI3), the right Arm IV length index (RALI4), and the hectocotylized proportion of the left Arm IV length (HcL%) between the two lineages. The differences between the two lineages were also supported by the analysis results for the number of sucker ring teeth. Accordingly, the results of the morphological analysis further confirmed the molecular analysis and provided additional evidence for the presence of the cryptic species of L. (N.) beka in the coastal areas of China.

A new species of deepwater tilefish, Branchiostegus sanaesp. nov., is described based on five specimens collected from the area between the Xisha Islands and Hainan Island, China. This species can be distinguished from congeners by its unique cheek marker and a combination of characteristics. Among the tilefish species known to be distributed in the South China Sea, this species is the only one with vertical stripes on the body. Based on the COI, CytB, and 12S sequences, a maximum-likelihood phylogenetic tree shows that the B. sanaesp. nov. forms a separate clade and is the sister group to the clade consisting of B. sawakinensis, B. albus, B. argentatus, B. biendong, B. japonicus, B. auratus, and B. okinawaensis. A key to the genus Branchiostegus is also compiled.

Cephalopod fisheries in the China Seas have witnessed an increasing trend in the catches of coastal cephalopods since the 1990s, with Loliginidae squid emerging as the main commercial target species. However, climate change and overfishing have led to a dramatic reduction in Loliginidae squid resources, highlighting the need to improve monitoring, protection, and management of this species. The Loligo beka and Uroteuthis duvaucelii are widely distributed along the coastal areas of the China Seas, and have commercial and ecological importance. Despite having overlapping distributions, similar life histories, and a strong dependence on the marine environment, there is limited knowledge about their growth and responses to environmental changes, hindering the effective management of their resources. In this study, we investigated the interspecies and intra-species differences in condition factor and their responses to temperature changes by analyzing data collected from wide coastal areas of the China Seas from June 2019 to November 2020. The findings showed that both species exhibited allometric growth and reproduced throughout the year, with two main breeding peaks. There were significant monthly variations and latitude differences in the intra-species growth, with a higher proportion of small-sized individuals (between 5 and 10 g for L. beka and between 10 and 20 g for U. duvaucelii) in low-latitude waters. The latitudinal differences in body weight and distribution between and within the two species were mainly due to natural habitats, especially temperature. Our mixed effect model results demonstrated that both species’ body weight increased with increasing temperature, suggesting that Loliginidae squid have significant environmental adaptability and can be used as an indicator species for studying environmental changes in the China Seas. These findings have significant implications for understanding the population dynamics, species development, and regionally specific management of Loliginidae squid fisheries in the China Seas.