Characteristics of the complete mitochondrial genome of Gerres limbatus (Cuvier, 1830) (Perciformes: Gerreidae)

Abstract The saddleback silver-biddy Gerres limbatus (Cuvier 1830) is distributed in Indo-West Pacific Oceans and associated with shallow coastal marine waters and estuaries. In this study, the complete mitochondrial genome of G. limbatus was firstly documented, which is 16,730 bp in length, including 13 protein-coding genes, 22 transfer RNA genes and 2 ribosomal RNA genes. The overall base composition of the mitochondrial genome is 26.42% A, 28.68% C, 27.32% T, and 17.58% G. The Maximum Likelihood phylogenetic tree was constructed based on COI gene of the 31 species from the family Gerreidae, with Heteroclinus puellarum and Hypopterus macropterus as outgroups. It revealed that G. erythrourus was placed as the sister group to G. limbatus.


Introduction
Genus Gerres is the largest in the eight genera of the family Gerreidae (Perciformes) and consists of 28 species (Nelson et al. 2016).Among these, 10 Gerres species are distributed in Chinese waters and are small to medium body sizes (fishdb.sinica.edu.tw,accessed 14 August 2023).Gerres species mainly feed on benthic animals, acting as low trophic level predators and transferring energy to higher trophic level predators (Chollet-Villalpando et al. 2014).Studies on the genus Gerres mainly focused on species taxonomy (Iwatsuki and Kimura 1998;Chollet-Villalpando et al. 2014).
The saddleback silver-biddy Gerres limbatus (Cuvier 1830) has a maximum of 15 cm in total length, and is mainly distributed in Indo-West Pacific Oceans, associated with shallow coastal marine waters and estuaries (www.fishbase.org,accessed 14 August 2023).In China, G. limbatus is common in the South China Sea and East China Sea (Liu et al. 2016).
The fish mitochondrial genome is a circular double-stranded DNA molecule, which has maternal inheritance, high copy number, high evolutionary rate and highly conserved (Boore 1999).To date, only four complete mitochondrial genomic sequences from the genus Gerres have been published (Ruan et al. 2020), including G. decacanthus, G. erythrourus, G. filamentosus and G. oyena.To fill in the data gaps at the molecular level, the complete mitochondrial genome of G. limbatus was sequenced.

Materials and methods
A fresh specimen of G. limbatus (Figure 1) was collected by a bottom trawler in April 2022 in Xiamen Bay, Fujian Province (24 � 30 0 14 00 N, 118 � 17 0 27 00 E).It was stored at −20 � C in the Fish Biology Laboratory of Xiamen University (Dr.Chen Wang, wangchen2971@163.com)under the voucher number XM2023023.Genomic DNA was extracted from the gill tissue using the Marine Animal Tissue Genomic DNA Extraction Kit (DP324, Tiangen, China).The Ex Taq TM Version 2.0 plus dye (Takara) was employed to amplify sequence by polymerase chain reaction (PCR).Parameters of PCR reaction were set according to the instructions.The PCR primers were provided by the Supplementary Table 1.
The base composition of the G. limbatus mitogenome is 26.42% A, 28.68% C, 27.32% T, and 17.58% G, with a slightly AT-rich feature (53.74%).Eight tRNA genes (tRNA-Ala, tRNA-Asn, tRNA-Cys, tRNA-Gln, tRNA-Glu, tRNA-Pro, tRNA-Ser (TGA), and tRNA-Tyr) and ND6 gene are encoded on the light chain, and other genes are encoded on the heavy chain.It has one control region, between tRNA-Pro gene and tRNA-Phe gene.The mitochondrial genome contains six overlapping regions and 18 intergenic regions.Most of the PCGs initiation codon is ATG, except COI gene starts with GTG.For the termination codons, nine PCGs (ATP6, ATP8, COI, COIII, ND1, ND2, ND4L, ND5 and ND6) are terminated with the complete stop codon TAA, and the others (COII, Cytb, ND3, and ND4) are ended with the incomplete stop codon T.
In the ML phylogenetic tree (Figure 3), the 16 Gerres species clustered a monophyletic group, located at the top of the Gerreidae phylogenetic tree with high support value.Gerres erythrourus clustered to G. limbatus as a sister group (bootstrap value ¼ 100), then clustered to G. longirostris and other Gerres species.

Figure 2 .
Figure 2. Graphic representation of the mitochondrial genome of Gerres limbatus.

Table 1 .
Features of the complete mitochondrial genome for Gerres limbatus.Positive values indicate distances between adjacent genes, negative values indicate the overlapping sequence of between adjacent genes.