Length–Weight Relationships of Eleven Deep-Sea Fishes (Order: Stomiiformes) from the South China Sea

The specimens were collected from the South China Sea, including the Xisha, Nansha, Dongsha, and northern slope waters (9°30′–20°30.01′N, 110°22′–116°09′E). Sampling was performed from May to November each year from 2014 to 2022 (except for 2020). The sampling phase covered 25 hauls over 13 cruises. The duration of each cruise was approximately 15 days. A mid-water trawl was used in the study with cod-end mesh size of 10 mm and 40 mm mesh in the forward section. Each haul began at around 12:00 a.m. and lasted for 1 h at a speed of 1.5–2.5 m/s at depths of 400–600 m. Fishes were immersed in seawater and stored immediately and independently at −40 °C. After each voyage, all specimens were identified in the onshore laboratory, and biological characteristics were collected for each individual, including total wet weight (TWW, to the nearest 0.01 g) and standard length (SL, to the nearest 0.1 cm). For each species, data accumulated from multiple cruises were analyzed as a whole in this study.

LWRs were determined by the formula W = aLb (Le-Cren, 1951; Froese, 2006), where W is TWW (g), L is SL (cm), a is the intercept of the regression curve, and b is the regression slope. Both a and b were estimated via the transformed logarithmic expression log(W) = log(a) + blog(L) (Froese, 2006). The coefficient of determination r2 was used to measure the fit of the model to the data. Confidence intervals (95%) of CL a and CL b were calculated in Origin version 9.9.0.225.

A total of 1095 stomiiform specimens were measured for LWRs (Table I). Summarized data including sample size (n), parameters a and b, ranges of TWW and SL, and coefficient of determination (r2) are presented in Table I. LWRs are presented for 11 species, representing Gonostomatidae (2 species) and Stomiidae (9 species). Parameter a ranged from 0.00180 for Diplophos taenia to 0.01833 for Borostomias pacificus, and b ranged from 2.64 for B. pacificus to 3.31 for Astronesthes indicus. All LWRs were highly significant (p < 0.01), with r2 ranging from 0.947 for Photonectes albipennis to 0.997 for Astronesthes cyaneus.

Sample sizes varied by species, ranging from 16 to 451 specimens, with rare species accumulated from multiple voyages. This study provides the first information on LWRs for 7 species, Astronesthes splendidus, A. cyaneus, A. indicus, B. pacificus, Heterophotus ophistoma, Idiacanthus fasciola, and P. albipennis, according to FishBase (Fishbase, 2023). New records of maximum length are provided for 3 species: A. cyaneus, A. splendidus, and B. pacificus. Estimates for CL b ranged from 2.64

Table I. Descriptive statistics and estimated LWRs parameters for eleven deep-sea fishes from order Stomiiformes in the South China Sea.

n, sample size; TWW, total wet weight; SL, standard length; a, initial growth index; b, slope of the regression; CL, confidence limits; r2, coefficient of determination. Bold, new LWR in Species or new maximum length in SL.

for B. pacificus to 3.31 for A. indicus. The sample sizes of Sigmops elongatus, Chauliodus sloani, and Malacosteus niger were greater than those of previous studies and together with D. taenia provided biological information on the Stomiiformes.

In the present study, specimens were preserved individually via a cryogenic seawater immersion method. Although we safeguarded the integrity of the specimens during measurement, especially from tooth loss, which is common for Stomiiformes, LWRs presented here may be slightly different from those found for living specimens because of the damage incurred during the haul, such as loss of scales and fins. Estimates for CL b ranged from 2.64 to 3.31 in the present study, within the expected range of 2.5 to 3.5 (an interval covering CL b values for most species proposed by Froese (2006), indicating that the specimens we used have the validity to reflect WLRs for these species. In addition, smaller individuals may have been missed, which might affect the b values for species due to selectivity of the mesh and the unknown nature of the early life history of Stomiiformes (Froese, 2006). In future studies, the sampling area and frequency should be increased to investigate the effects of gender and regional differences on LWRs. Some previous investigations comparing eviscerated and non-eviscerated fish have revealed some differences, especially in predatory fish, which should also be noted in future studies (Froese, 2006; Knutsen et al., 2023). In conclusion, the basic information provided here will help fill gaps in biological knowledge of the Stomiiformes and contribute to the understanding of deep-sea fishes in the South China Sea.

We thank the staff of R/V Nanfeng for collecting specimens.

This work was supported by the the Financial Fund of the Ministry of Agriculture (NHZX2024), the Major Projects of Basic and Applied Basic Research Programs in Guangdong Province (2019B030302004), and the Central Public Interest Scientific Institution Basal Research Fund of the Chinese Academy of Fishery Sciences (2023TD05).

The animal study was reviewed and approved by the South China Sea Fisheries Research Institute Animal Welfare Committee (Ethical approval number: SCSFRI Document number 40/2016). Approval date: 18 March 2016.

The author declares that the sampling of the species under investigation was conducted in accordance with the international conventions on the use of animals in scientific research.

During the preparation of this article, the author did not utilize generative AI and AI-assisted technology.

The authors have declared no conflict of interest.