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Length-weight and length-length relationships of 16 marine fish species in Vietnam

ABSTRACT

In this study, the length-weight relationships (LWRs) and length-length relationships (LLRs) of 16 marine fish species-important component of fishery production models-were estimated. The specimens were collected monthly from commercial gillnet fisheries from November 6, 2018 to October 30, 2019 in Vietnamese waters. In total, 7,426 individuals had their total length (TL), fork length (FL) and total body weight (W) measured. LWRs were calculated using the logarithmic transformation of the linear regression equation logW = loga + b*logTL, while LLRs were determined using a linear regression model: TL = a + b*FL. In addition, 95% confidence intervals (CIs) were estimated for the model parameters. The results showed that all regression parameters were highly significant (p < 0.001), with coefficients of determinations (R 2 ) > 0.9412 for all species. The a (intercept) values ranged from 0.0025 to 0.4, and the b (slope) values ranged from 2.53 to 3.28. TL and FL were highly correlated (p < 0.001 and R 2 > 0.9422 for all parameters), and a and b ranged from -9.12 to 15.85 and 0.87 to 1.45, respectively. The results provide the key morphology parameters, which are beneficial for fishery researchers and managers in stock assessment, administration and conservation.

Keywords:
Vietnamese fisheries; Morphology; Allometry; Stock assessment; Fisheries management

Vietnam has an extensive coastline of more than 3,260 km and an exclusive economic zone (EEZ) of more than one million km2, including islands and archipelagos, bays, lagoons and fjords, which provide a diverse residential habitat and environment for marine species. More than 2,000 marine species, including approximately 130 commercial species, have been recorded in Vietnamese waters (Uyen, 2017Uyen, N. T. 2017. Fisheries country profile: Vietnam. Regional Fisheries Policy Network (RFPN) Member for Viet Nam. Bangkok, Southeast Asian Fisheries Development Center. Available from: Available from: http://www.seafdec.org/fisheries-country-profile-viet-nam/ Acess date: Feb 10, 2023.
http://www.seafdec.org/fisheries-country...
). The exploitation of marine fishery resources is the major economic contributor to coastal provinces, provides employment opportunities for the local population and is an important source of animal protein and micronutrients (Raakjær et al., 2007Raakjær, J., Manh Son, D., Stæhr, K. J., Hovgård, H., Dieu Thuy, N. T., Ellegaard, K., Riget, F., Van Thi, D. & Giang Hai, P. 2007. Adaptive fisheries management in Vietnam. The use of indicators and the introduction of a multi-disciplinary Marine Fisheries Specialist Team to support implementation. Marine Policy , 31(2), 143-152. ; Pomeroy et al., 2009Pomeroy, R., Thi Nguyen, K. A. & Thong, H. X. 2009. Small-scale marine fisheries policy in Vietnam. Marine Policy, 33(2), 419-428. ; Nguyen et al., 2017Nguyen, D. B., Momtaz, S., Zimmerman, K. & Pham, T. H. N. 2017. Effectiveness of formal institutions in managing marine fisheries for sustainable fisheries development: A case study of a coastal commune in Vietnam. Ocean and Coastal Management, 137, 175-184. ). The marine fishery economic sector contributes 5% of the gross domestic product and provides approximately 4 million jobs for the local population (VASEP, 2020VASEP. 2020. Report on Vietnam seafood exports in 2019. Ha Noi City, Vietnam Association of Seafood Exporters and Producers.). Vietnam is one of the top ten seafood exporting countries in the world, and in 2019, marine landings in the country reached 3.73 million tons, with an export value of more than five billion USD (FAO, 2020FAO (Food and Agriculture Organization of the United Nations). 2020. The state of world fisheries and aquaculture 2020. Sustainability in action. Rome, FAO. DOI: https://doi.org/10.4060/ca9229en.
https://doi.org/10.4060/ca9229en...
; VASEP, 2020VASEP. 2020. Report on Vietnam seafood exports in 2019. Ha Noi City, Vietnam Association of Seafood Exporters and Producers.). However, marine resources have shown signs of decline resulting from the decrease in the catch rate of key fisheries over time and in the catch sizes of many species (Nguyen et al., 2021Nguyen, K. Q., Do, M. D., Phan, H. T., Nguyen, L. T., To, P. V., Vu, N. K., & Tran, P. D. 2021. Catch composition and codend selectivity of inshore trawl fishery with the legal minimum mesh size. Regional Studies in Marine Science, 47, 101977. ; 2022aNguyen, K. Q., Nguyen, B.V., Phan, H. T., Nguyen, L. T., To, P. V. & Tran, H. V. 2022a. A comparison of catch efficiency and bycatch reduction of tuna pole-and-line fisheries using Japan tuna hook (JT-hook) and circle-shaped hook (C-hook). Marine and Freshwater Research, 73(5), 662-677. ). To solve these issues and maintain sustainable fisheries, the government of Vietnam approved the national development program on efficient and sustainable fishing for the period from 2022 to 2025, with guidance for 2030, in which it emphasizes a Total Allowable Catch (TAC) and quota allocation management system (Vietnam, 2022Vietnam. 2022. Decision No. 1090/QD-TTg dated September 19, 2022 on approval for national development program on efficient and sustainable fishing in the 2022-2025 period, with orientation towards 2030. Ha Noi City, Prime Minister. ). Although the sustainable exploitation of marine fish species brings clear benefits, it is difficult to develop effective management guidelines for most commercial species in Vietnam because there is no information on their biological and demographic characteristics (Nguyen and Nguyen, 2014Nguyen, Q. C., & Nguyen, V. C. 2014. Intergrated coastal management in Vietnam: current situation and orientation. Journal of Marine Science and Technology, 14(1), 89-96. ). In particular, length-weight relationship (LWR) and length-length relationship (LLR) data, which are important components of fishery production and stock assessment models, do not exist for any of the species populations assessed in this study.

Length-weight relationships (LWRs) and length-length relationships (LLRs) calculated according to correlation coefficients and regressions make it possible to evaluate fish biomass, stock assessments, ecological studies and taxonomic identification and are very important for the management and conservation of fisheries to regulate catches (Froese, 2006Froese, R. 2006. Cube law, condition factor and weight-length relationships: History, meta-analysis and recommendations. Journal of Applied Ichthyology , 22(4), 241-253. ). In addition, LWRs can be used as condition factors to compare the health of individuals and populations that can be influenced by environmental conditions and sexual variables (Tesch, 1968Tesch, F. W. 1968. Age and growth. In: Ricker, W. E. Methods for Assessment of Fish Production in Fresh Waters (pp. 93-123). Hoboken: Blackwell Scientific Publications.; Froese, 2006Froese, R. 2006. Cube law, condition factor and weight-length relationships: History, meta-analysis and recommendations. Journal of Applied Ichthyology , 22(4), 241-253. ). In some cases, it is not possible to measure total length (TL) in the port because the fishermen carry out preliminary treatments at sea, including the removal of fins and tails, to improve the quality of the fish (Nguyen et al., 2022aNguyen, K. Q., Nguyen, B.V., Phan, H. T., Nguyen, L. T., To, P. V. & Tran, H. V. 2022a. A comparison of catch efficiency and bycatch reduction of tuna pole-and-line fisheries using Japan tuna hook (JT-hook) and circle-shaped hook (C-hook). Marine and Freshwater Research, 73(5), 662-677. ), resulting in the loss of biometric data, which are necessary for fishery analyses and modeling. Size conversions (e.g. TL calculated based on FL) are therefore necessary for species comparison (Nguyen et al., 2022bNguyen, K. Q., Phan, H. T., Tran, P. D., Nguyen, B. V., Do, T. V., Nguyen, L. T., To, P. V., & Vu, N. K. 2022b. Length-length, length-weight, and weight-weight relationships of yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tuna collected from the commercial handlines fisheries in the South China Sea. Thalassas, 38, 911-917. ). The classification of fish development and growth relies on positive and negative allometries (Froese, 2006Froese, R. 2006. Cube law, condition factor and weight-length relationships: History, meta-analysis and recommendations. Journal of Applied Ichthyology , 22(4), 241-253. ).

In Vietnam, very few studies on the LWR and LLR of marine fish species have been documented. As far as we know, work has been done on Yellowfin (Thunnus albacares Bonnaterre, 1788) and Bigeye (Thunnus obesus Lowe, 1839) Tuna (Nguyen et al., 2022bNguyen, K. Q., Phan, H. T., Tran, P. D., Nguyen, B. V., Do, T. V., Nguyen, L. T., To, P. V., & Vu, N. K. 2022b. Length-length, length-weight, and weight-weight relationships of yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tuna collected from the commercial handlines fisheries in the South China Sea. Thalassas, 38, 911-917. ), mudskipper (Periophthalmus variabilis Eggert, 1935) (Dinh et al., 2022aDinh, Q. M., Nguyen, T. H. D., Nguyen, T. T. K., Tran, G. V. & Truong, N. T. 2022a. Spatiotemporal variations in lengthweight relationship, growth pattern and condition factor of Periophthalmus variabilis Eggert, 1935 in Vietnamese Mekong Delta. PeerJ, 10. DOI: https://doi.org/10.7717/peerj.12798
https://doi.org/10.7717/peerj.12798...
), mullet (Ellochelon vaigiensis Quoy and Gaimard, 1825) (Dinh et al., 2022bDinh, Q. M., Truong, N. T., Duc Nguyen, T. H., Huyen Tran, L. T., Kieu Nguyen, T. T. & Phan, L. H. 2022b. Variations in length-weight relationship, growth and body condition of the commercial mullet Ellochelon vaigiensis in the Vietnamese Mekong Delta. Heliyon, 8(11), e11789. ), and a few other fish species in the Gulf of Tonkin, northern Vietnam (Wang et al., 2011Wang, X. H., Qiu, Y. S., Zhu, G. P., Du, F. Y., Sun, D. R. & Huang, S. L. 2011. Length-weight relationships of 69 fish species in the Beibu Gulf, northern South China Sea. Journal of Applied Ichthyology , 27(3), 959-961. ). In this context, this study aimed to provide information on the LWRs and LLRs of 16 marine fish species in Vietnam, to identify the growth type of each species and to contribute to understanding the biological and demographic information of these fish communities.

The specimens were collected using gillnets in the Gulf of Tonkin (Latitude: 19.615°N - 20.28°N; Longitude: 106.631°E - 107.375°E), center (Latitude: 11.068°N - 11.431°N; Longitude: 109.192°E - 109.688°E) and south (Latitude: 9.085°N - 9.955°N; Longitude: 106.625°E - 107.559°E) of Vietnam from November 6, 2018 to October 30, 2019 (Figure 1). The gillnets were 450 m long x 28 m high, constructed in dark green polyethylene (PE) twine with a diameter of 1.5 mm, forming knotted mesh opening sizes ranging from 125 to 180 mm (Nguyen et al., 2023Nguyen, L. T., Nguyen, K. Q., & Nguyen, T. P. 2023. Experimental Mixed Gillnets Improve Catches of Narrow-Barred Spanish Mackerel (Scomberomorus commerson). Fishes, 8(4), 210. ). The depth at the sampling site ranged from 46 to 128 m (mean: 76 m) (Figure 1). Fishing operations were carried out at night, with a mean soak time of 6.9 hours (ranging from 2.2 to 11.8 hours). After removing the gillnets, the catch was separated to the species level based on the FishBase classification (Froese and Pauly, 2023Froese, R. & Pauly, D. 2023. World register of marine species. Available at: Available at: https://www.marinespecies.org/index.php Acess date: Jun 29, 2023.
https://www.marinespecies.org/index.php...
). TL was measured from the tip of the snout to the end of the longest lobe of the caudal fin, and FL was measured from the tip of the jaw to the center of the tail fork. Both sizes were measured in millimeters using a measurement board. The total weight (W), measured in grams, was recorded for each individual using a digital scale.

Figure 1
Map of Vietnam including the study sites in the South China Sea. Each red dot indicates the position of each gillnet deployed. Multiple sets could be deployed in the same or close locations.

The parameters of the LWRs were calculated after the logarithmic transformation of the power regression W=aTLb into the linear regression logW=loga+b*logTL. The TL and FL relationships were established using a linear regression model with the formula TL=a+b*FL, in which a is the intercept and b is the regression parameter (slope of the model). Before adjusting the regression analysis, outliers were tested and removed following the method of Froese (2006Froese, R. 2006. Cube law, condition factor and weight-length relationships: History, meta-analysis and recommendations. Journal of Applied Ichthyology , 22(4), 241-253. ). The b values obtained from the regression models can inform the growth patterns of the fish, including positive allometric, negative allometric and isometric ones (Froese, 2006Froese, R. 2006. Cube law, condition factor and weight-length relationships: History, meta-analysis and recommendations. Journal of Applied Ichthyology , 22(4), 241-253. ). If the value of b is significantly smaller than three, the fish has negative allometric growth; if b is significantly greater than three, the fish has positive allometric growth; and if b is close to three (not significantly different from three), the fish has isometric growth (Froese, 2006Froese, R. 2006. Cube law, condition factor and weight-length relationships: History, meta-analysis and recommendations. Journal of Applied Ichthyology , 22(4), 241-253. ). To confirm the significant difference of b values from the isometric values (b= ~3), a 95% confidence interval (CI) (α = 0.05) was applied, obtained from the equation ts = (b-3)/sb, in which ts is the t-test value and sb is the standard error of the slope (b) (Sokal and Rohlf, 1987Sokal, R. R. & Rohlf, F. J. 1987. Introduction to biostatistics, 2. Ed. Freeman Publication, New York.). The levels of statistical significance of the coefficient of determination (R2) were also estimated. The open software R-statistical (V4.1.2) (R Core Team, 2021R Core Team. 2021. The R project for statistical computing. Available from: Available from: https://cran.r-project.org/bin/windows/base/ Acess date: Feb 10, /2023.
https://cran.r-project.org/bin/windows/b...
) was used to carry out all the analyses, prepare the data and produce the figures. LWRs and LLRs were assessed with the Simple Fisheries Stock Assessment Method package (Ogle et al., 2023Ogle, D. H., Doll, J. C., Wheeler, A. P. & Dinno A. 2023. Package “FSA”: Simple Fisheries Stock Assessment Methods. Available from: Available from: https://fishr-core-team.github.io/FSA/ Acess date: Mar 20, 2023.
https://fishr-core-team.github.io/FSA/...
).

In total, 7,426 specimens, belonging to 16 species, 10 families and seven orders had their LWRs and LLRs analyzed (Table 1). All species were captured in sufficient numbers to conduct the statistical analysis. The results indicated that the estimated regression of the LWRs was statistically significant (p < 0.001) for all parameters and all species and that R2 ranged from 0.9412 to 0.9991 (Table 2). The total variation of a was from 0.0025 to 0.4, and b ranged from 2.53 to 3.28 (Table 2). The relationship between TL and FL was highly linear (R2 > 0.9422) and significant (p < 0.001) for all species (Table 2). The intercept (a) ranged from -9.12 (Coryphaena hippurus Linnaeus, 1758) to 15.85 (Scomberomorus guttatus Bloch and Schneider, 1801). The regression coefficient (b) ranged from 0.87, for Scomberomorus guttatus, to 1.45, for Mene maculate (Bloch and Schneider, 1801) (Table 2).

Table 1
Summary details of the number of samples (n), weight (W) and length (TL: Total length; FL: Fork length) of 16 fish species collected from November 6, 2018 to October 30, 2019 using gillnets in Vietnamese waters.

Table 2
Descriptive statistics and estimated parameters of the length-weight relationship and length-length relationship of 16 fish species from Vietnamese waters.

The values of the allometric coefficient b for all the species assessed in our study, which indicates the isometric growth pattern, are within the expected range of the meta-analysis (2.5 - 3.5) reported by Froese (2006Froese, R. 2006. Cube law, condition factor and weight-length relationships: History, meta-analysis and recommendations. Journal of Applied Ichthyology , 22(4), 241-253. ). Our results show that the coefficient parameters for the length-weight and length-length relationships are highly significant (p < 0.001), with R2 > 0.9412. This indicates that the analyzed models are well fit and robust. Moreover, the specimens were sampled onboard the fishing vessels, with no shrinking or dehydration of the body of the fish, which occur when the samples are fixed in alcohol and formaldehyde (Parker, 1963Parker, R. R. 1963. Effects of formalin on length and weight of fishes. Journal of the Fisheries Research Board of Canada, 20(6), 1441-1455. ). The sampling of specimens from commercial fisheries resulted, for the most part, in matured-sized individuals. Therefore, the model parameters (a and b) and the values of the coefficient of determination could be improved by sampling all length and weight ranges of the fish in the population, including small fish.

Hyperallometry (b > 3; min CI of b > 3) was observed in two species (Polynemus indicus Linnaeus, 1758 and Scomberomorus commerson Lacepède, 1800), with the length increase rate being lower than the weight increase rate (Froese, 2006Froese, R. 2006. Cube law, condition factor and weight-length relationships: History, meta-analysis and recommendations. Journal of Applied Ichthyology , 22(4), 241-253. ; Karachle and Stergiou, 2012Karachle, P. K. & Stergiou, K. I. 2012. Morphometrics and allometry in fishes. In: Wahl, C. (Ed.). Morphometrics (pp. 65-86). London: IntechOpen. ). The species Mene maculate (Bloch and Schneider, 1801), Lutjanus erythropterus (Bloch, 1790), Thunnus obesus (Lowe, 1839) and Acanthocybium solandri (Cuvier, 1832) have hypoallometric characteristics, with a lower rate of weight increase than of length increase (b < 3; max CI of b < 3) (Froese, 2006Froese, R. 2006. Cube law, condition factor and weight-length relationships: History, meta-analysis and recommendations. Journal of Applied Ichthyology , 22(4), 241-253. ; Karachle and Stergiou, 2012Karachle, P. K. & Stergiou, K. I. 2012. Morphometrics and allometry in fishes. In: Wahl, C. (Ed.). Morphometrics (pp. 65-86). London: IntechOpen. ). The remaining species are isometric, with proportional weight and length increase rates (CI of b varying within 3) (Froese, 2006Froese, R. 2006. Cube law, condition factor and weight-length relationships: History, meta-analysis and recommendations. Journal of Applied Ichthyology , 22(4), 241-253. ; Karachle and Stergiou, 2012Karachle, P. K. & Stergiou, K. I. 2012. Morphometrics and allometry in fishes. In: Wahl, C. (Ed.). Morphometrics (pp. 65-86). London: IntechOpen. ).

LWRs also depend on intraspecific (e.g. sex and age), temporal (e.g. season) and environmental (e.g. temperature, salinity and food availability) conditions (Cort et al., 2015Cort, J. L., Estruch, V. D., dos Santos, M. N., Di Natale, A., Abid, N. & de la Serna, J. M. 2015. On the variability of the length-weight relationship for Atlantic bluefin tuna, Thunnus thynnus (L.). Reviews in Fisheries Science and Aquaculture, 23(1), 23-38. ; Compaire and Soriguer, 2020Compaire, J. C. & Soriguer, M. C. 2020. Length-weight relationships of seven fish species from tidepools of an intertidal rocky shore in the Gulf of Cadiz, Spain (NE Atlantic). Journal of Applied Ichthyology, 36, 852-854.). The variation in species growth between our study and some other reports may be related to differences in the studied areas and fishing gear used. Our study was conducted in the upwelling areas of the South China Sea (Hu and Wang, 1988Hu, J. & Wang, X. H. 1988. Progress on upwelling studies in the China seas. Reviews of Geophysics, 69(37), 849-849. ; Kuo et al., 2000Kuo, N. J., Zheng, Q. & Ho, C. R. 2000. Satellite observation of upwelling along the western coast of the South China Sea. Remote Sensing of Environment, 74(3), 463-470. ; Xie et al., 2003Xie, S. P., Xie, Q., Wang, D. & Liu, W. T. 2003. Summer upwelling in the South China Sea and its role in regional climate variations. Journal of Geophysical Research: Oceans, 108(8), 1-13. ), which are rich in organic material and prey sources. Therefore, most of the species evaluated in this study show faster growth rates than those in other marine areas (Uchiyama and Boggs, 2006Uchiyama, J. H. & Boggs, C. H. 2006. Length-weight relationships of Dolphinfish, Coryphaena hippurus and Wahoo, Acanthocybium solandri: Seasonal effects of spawning and possible migration in the central North Pacific. Marine Fisheries Review, 68(1-4), 19-29.; Sawant and Raje, 2009Sawant, P. B. & Raje, S. G. 2009. Morphometry and length weight relationship of the catfishes Arius Caelatus (Valenciennes, 1840) and Arius thalassinus (Ruppell, 1837) off Mumbai, Veraval and Vishakhapatanam coasts. Asian Fisheries Science, 22(1), 215-228. ; Zhu et al., 2009Zhu, G., Xu, L., Zhou, Y., Song, L. & Dai, X. 2009. Length-Weight relationships for bigeye tuna (Thunnus Obesus), yellowfin Tuna (Thunnus Albacares) and albacore (Thunnus Alalunga) (Perciformes: Scombrinae) in the Atlantic, Indian and Eastern Pacific Oceans. Collective Volume of Scientific Papers ICCAT, 65(2), 717-724.; Ahmed et al., 2014Ahmed, Q., Khan, D. & Yousuf, F. 2014. Length-Weight Relationship in Adult Scomberomorus Guttatus (Bloch & Schneider, 1801) From Karachi Coast, Pakistan. International Journal of Biology Research, 2(2), 101-107.; Fakhri et al., 2015Fakhri, A., Fekrandish, H., Pazira, A. & Rastgoo, A. 2015. Length-weight relationship and growth parameters of kingfish (Scomberomorus commerson) in the North of the Persian Gulf. Journal of Fisheries and Aquatic Science, 10(6), 592-596. ; Lelono et al., 2021Lelono, T. D., Bintoro, G., Setyohadi, D. & Risky, M. 2021. The length-weight relationships and clasper maturity of two shark (Carcharhinus sorrah, Carcharhinus falciformis) of landed in Prigi Coastal fishing Port Trenggalek East Jawa. IOP Conference Series: Earth and Environmental Science, 860(1). ). We collected specimens using commercial gillnets that captured substantial mature-sized fish, while other studies have used multiple methods, such as trawling, longlining, angling, purse seine fishing and port-based sampling, which included a wide range of sizes (Sawant and Raje, 2009Sawant, P. B. & Raje, S. G. 2009. Morphometry and length weight relationship of the catfishes Arius Caelatus (Valenciennes, 1840) and Arius thalassinus (Ruppell, 1837) off Mumbai, Veraval and Vishakhapatanam coasts. Asian Fisheries Science, 22(1), 215-228. ; Zhu et al., 2009Zhu, G., Xu, L., Zhou, Y., Song, L. & Dai, X. 2009. Length-Weight relationships for bigeye tuna (Thunnus Obesus), yellowfin Tuna (Thunnus Albacares) and albacore (Thunnus Alalunga) (Perciformes: Scombrinae) in the Atlantic, Indian and Eastern Pacific Oceans. Collective Volume of Scientific Papers ICCAT, 65(2), 717-724.; Ahmed et al., 2014Ahmed, Q., Khan, D. & Yousuf, F. 2014. Length-Weight Relationship in Adult Scomberomorus Guttatus (Bloch & Schneider, 1801) From Karachi Coast, Pakistan. International Journal of Biology Research, 2(2), 101-107.; Fakhri et al., 2015Fakhri, A., Fekrandish, H., Pazira, A. & Rastgoo, A. 2015. Length-weight relationship and growth parameters of kingfish (Scomberomorus commerson) in the North of the Persian Gulf. Journal of Fisheries and Aquatic Science, 10(6), 592-596. ; Lelono et al., 2021Lelono, T. D., Bintoro, G., Setyohadi, D. & Risky, M. 2021. The length-weight relationships and clasper maturity of two shark (Carcharhinus sorrah, Carcharhinus falciformis) of landed in Prigi Coastal fishing Port Trenggalek East Jawa. IOP Conference Series: Earth and Environmental Science, 860(1). ; Nguyen et al., 2022Nguyen, K. Q., Nguyen, B.V., Phan, H. T., Nguyen, L. T., To, P. V. & Tran, H. V. 2022a. A comparison of catch efficiency and bycatch reduction of tuna pole-and-line fisheries using Japan tuna hook (JT-hook) and circle-shaped hook (C-hook). Marine and Freshwater Research, 73(5), 662-677. ). In addition to incomplete information on the LWRs and LLRs of the species investigated, the length-at-age, length-at-maturity and growth rate of these species in Vietnamese waters-important biological factors needed to carry out a stock assessment-are unknown. This suggests that there is room for further research into the ecology and demographics of marine species.

Although knowledge about LWRs is critical for the fish ecology model, LLRs provide the key body shape parameter that can be used to back-calculate between TL, FL and W. In some cases, TL and W are not available because fishermen remove fins, viscera and gills before handling fish (Nguyen et al., 2022aNguyen, K. Q., Nguyen, B.V., Phan, H. T., Nguyen, L. T., To, P. V. & Tran, H. V. 2022a. A comparison of catch efficiency and bycatch reduction of tuna pole-and-line fisheries using Japan tuna hook (JT-hook) and circle-shaped hook (C-hook). Marine and Freshwater Research, 73(5), 662-677. ). TL is used to determine the legal sizes for commercial and recreational fishing in Vietnam (Nguyen et al., 2021Nguyen, K. Q., Do, M. D., Phan, H. T., Nguyen, L. T., To, P. V., Vu, N. K., & Tran, P. D. 2021. Catch composition and codend selectivity of inshore trawl fishery with the legal minimum mesh size. Regional Studies in Marine Science, 47, 101977. ). Therefore, reliable LLRs are needed for data conversion and management. The LLR analysis is consistent with the LWRs in terms of fish growth patterns, as most species have isometric growth patterns, with an LLR coefficient not significantly greater than the value of unity (b = 1). In other words, the caudal fin does not increase proportionally to the increase in the length of the fish. However, two species were found to have hyperallometric (b > 1) and four were found to have hypoallometric (b < 1) characteristics.

In conclusion, information on the biological aspects and morphological parameters of marine fish species in Vietnamese waters is quite insufficient (Nguyen and Nguyen, 2014Nguyen, Q. C., & Nguyen, V. C. 2014. Intergrated coastal management in Vietnam: current situation and orientation. Journal of Marine Science and Technology, 14(1), 89-96. ). Thus, fish stock assessments, ecological studies and taxonomic identification cannot be carried out for many marine species, including the 16 species investigated in this study. This is the first time that LWRs and LLRs have been documented for these species in Vietnam. This study fills scientific information gaps in basic biological knowledge and provides useful information for the development and management of sustainable fisheries, studies on fish population dynamics and scientific tools for future studies. The length-weight and length-length relationships of the 16 species described here provide new information and biological parameters in Vietnam. This can help researchers and fisheries managers carry out further studies and develop appropriate management strategies and policies.

ACKNOWLEDGMENTS

The author would like to thank the Institute of Marine Science and Fishing Technology of Nha Trang University for providing the means to carry out this study. He also thanks Dr. Phu Tran for consulting on the statistical analyses and providing comments and edits on an earlier version of the manuscript. Lastly, the author would like to thank the Editors, Associate Editors and Reviewers for their helpful comments and improvements throughout the peer review process.

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  • Cort, J. L., Estruch, V. D., dos Santos, M. N., Di Natale, A., Abid, N. & de la Serna, J. M. 2015. On the variability of the length-weight relationship for Atlantic bluefin tuna, Thunnus thynnus (L.). Reviews in Fisheries Science and Aquaculture, 23(1), 23-38.
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Edited by

Associate Editor:

Margit Wilhelm

Publication Dates

  • Publication in this collection
    29 Mar 2024
  • Date of issue
    2024

History

  • Received
    31 Mar 2023
  • Accepted
    27 Jan 2024
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