Otolith-fish length relationships in mesopelagic myctophids from the Southwestern Atlantic OceanABSTRACT
Mesopelagic fishes play a central role in marine carbon export and trophic dynamics, with lanternfishes (Myctophidae) representing one of the most abundant and diverse vertebrate groups in the worldʼs oceans. Despite their ecological significance, quantitative relationships between otolith size and body size remain poorly documented for many mesopelagic taxa, limiting their application in dietary studies and palaeontological reconstructions. In this study, we examined sagittal otoliths from nine Myctophidae species (Ceratoscopelus warmingii, Dasyscopelus obtusirostris, Diaphus dumerilii, D. hudsoni, D. perspicillatus, Hygophum hygomii, Lepidophanes guentheri, Notoscopelus caudispinosus, and N. resplendens) collected along the Southeastern Brazilian continental margin between 1996 and 1999. Otoliths were digitally imaged, and morphometric parameters, including otolith length (OL) and width (OW), were measured to assess their relationship with total length (TL) and standard length (SL) using linear regression analyses. Significant positive correlations were observed between otolith dimensions and fish length for most species. Both OL and OW were reliable predictors of TL and SL, except for L. guentheri and N. resplendens. This study provides new regression data that are likely to greatly facilitate the estimation of myctophid size in dietary and paleontological studies.
Keywords:
Sagittae; Mesopelagic fishes; Lanternfishes; Otolith-fish body relationships; Linear regression
Mesopelagic organisms play a key role in the export of organic carbon from the ocean surface to deeper layers, acting as a crucial link in the marine food web between primary consumers (e.g., zooplankton) and top predators such as tunas, sharks, cetaceans, pinnipeds, and seabirds (Anderson et al., 2019; Saba et al., 2021). Therefore, any adverse impacts resulting from ocean warming on these organisms directly affect the oceanʼs capacity to sequester atmospheric carbon into deeper oceanic regions (Agiadi et al., 2022). Myctophids are the most successful clade of mesopelagic fish in the Southern Ocean. They are widely distributed, speciose, and abundant, with 34 species and an estimated biomass that may substantially exceed 70-200 million tonnes (Zanchin et al., 2025). Their systematically arranged photophores, extensive diel vertical migrations between mesopelagic and epipelagic zones, and adaptations to low-oxygen environments (Hidalgo and Browman, 2019) further highlight their uniqueness.
In the Southwestern Atlantic, Myctophidae species have been studied regarding their larval development (Bonecker et al., 2014; Katsuragawa et al., 2014), hydroacoustic surveys (Weigert and Madureira, 2011), taxonomy and ecology (Braga et al., 2014; Martins et al., 2025), trophic position (Olivar et al., 2018), biogeography and distribution (Rintz et al., 2025; Zanchin et al., 2025), and otolith morphology (Giaretta et al., 2017; Haimovici et al., 2024; Rossi-Wongtschowski et al., 2016).
Sagittal otoliths found in predator stomachs provide valuable insights into understanding trophodynamics, offering information on prey species identity, size, weight, and energy content (Byrd et al., 2020; Lin et al., 2020; Saunders et al., 2020). Moreover, otolith taxonomic, morphological, and morphometric studies (Battaglia et al., 2015; Quigley et al., 2023; Saunders et al., 2020) are also important prerequisites for palaeoichthyological studies (Schwarzhans and Carnevale, 2021) and for the reconstruction of individual fish weight or size (Agiadi et al., 2023). However, such applications depend on robust species-specific relationships between otolith dimensions and fish length and weight relationships that remain undocumented or poorly described for many mesopelagic species.
The aim of this study is to provide a helpful tool for dietary and paleontological research by estimating the relationship between otolith length and fish length in nine lanternfish species from the continental margin off Southeastern Brazil: Ceratoscopelus warmingii (Lütken, 1892) - Warming’s lantern fish; Dasyscopelus obtusirostris (Tåning, 1928) - Bluntsnout lanternfish; Diaphus dumerilii (Bleeker, 1856) - Dumeril’s lanternfish; Diaphus hudsoni Zurbrigg & Scott, 1976 - Hudson’s lanternfish; Diaphus perspicillatus (Ogilby, 1898) - Transparent lanternfish; Hygophum hygomii (Lütken, 1892) - Bermuda lanternfish; Lepidophanes guentheri (Goode & Bean, 1896) - Günther’s lanternfish; Notoscopelus caudispinosus (Johnson, 1863) - Lobisomem; and Notoscopelus resplendens (Richardson, 1845) - Patchwork lampfish.
Fish specimens were collected using midwater trawls between 1996 and 1999 during the REVIZEE Program - Southeast-South Score (Programa de Avaliação do Uso e Gerenciamento Sustentável dos Recursos Pesqueiros - Score Sudeste-Sul, in Brazilian Portuguese; Madureira et al., 2005). In the laboratory, data on total length, standard length, and total weight of each individual were taken, and the otoliths were removed, cleaned and stored.
The otoliths and associated biometric data used in this study belong to the Collection of Marine Fish Otoliths from the Southeast-South Region of Brazil (COSS-Brasil; Coleção de Otólitos de Peixes Marinhos da Região Sudeste-Sul do Brasil, in Portuguese; Rossi-Wongtschowski et al., 2016) housed in the Oceanographic Institute of the University of São Paulo. Image acquisition consisted of positioning sagittal otoliths with their external surface facing downward, thereby exposing the sulcal groove on top and orienting the sagitta so that the sulcus is in the horizontal plane. Two-dimensional orthogonal digital photographs of the otoliths were taken using a modular stereo microscope equipped with a motorized zoom (ZEISS SteREO Discovery.V12) set to 12× magnification. High-contrast images were captured using Axion Vision 4.8 software, which utilizes reflected light against a dark background to produce bright images. Following binarization of the grayscale otolith images, each otolith was quantitatively characterized through morphometric parameters, including otolith length (OL) and otolith width (OW). These were the maximum otolith length and width, measured with the sulcus in the horizontal plane, in millimeters, using ImageJ software (version 1.51q; Rasband, 2018). Linear regression (y = ax+b) was used to relate total length (TL) to standard length (SL), as well as TL and SL to OL and OW (Battaglia et al., 2015; Saunders et al., 2020).
This study provides valuable information about Myctophidae species on the continental margin of Southeastern Brazil. Otoliths of each evaluated species are shown in Figure 1. Our results showed that otolith size (length and width) and fish length (total and standard) were significantly correlated for most species we examined (Table 1). Equations that presented r2 values lower than 0.1 were suppressed from Table 1 due to a lack of biological meaning. Both otolith length and otolith width yielded informative, statistically significant regressions, except for Lepidophanes guentheri and Notoscopelus resplendens.
Sagittal otoliths from nine Myctophidae species deposited in the Collection of Marine Fish Otoliths from the Southeast-South Region of Brazil (COSS-Brasil; Coleção de Otólitos de Peixes Marinhos da Região Sudeste-Sul do Brasil, in Portuguese). Fish standard length (SL) of each otolith: TLCEWA = 64 mm; TLDAOB = 62 mm; TLDIDU = 62 mm; TLDIHU = 72 mm; SLDIPE = 46 mm; SLHYHY = 60 mm; SLLEGU = 62 mm; SLNOCA = 40 mm; SLNORE = 67 mm.
Summary of morphometric descriptions and biometric relationships between specimen size and otolith dimensions for Ceratoscopelus warmingii, Dasyscopelus obtusirostris, Diaphus dumerilii, Diaphus hudsoni, Diaphus perspicillatus, Hygophum hygomii, Lepidophanes guentheri, Notoscopelus caudispinosus, Notoscopelus resplendens. n: number of left sagittal otoliths analyzed; TL (gray background) and SL (white background): total and standard length, respectively (mm); TW: total body mass (g); OL: otolith length (mm); OW: otolith width (mm); a and b: linear equation parameters of slope and y-intercept, respectively.
While specimens of L. guentheri exhibited the smallest otoliths, those of the genus Diaphus had the largest otoliths analyzed (Table 1). Moreover, the coefficients of determination for the equations relating TL and SL, TL/SL and OL, and TL/SL and OW indicate, in general, a good fit of the data to the linear regression model. Exceptions were N. resplendens, which had the smallest number of available samples and the narrowest size range, and L. guentheri, for which the relationships between body and otolith dimensions did not fit a linear model. Otolith length usually shows a more robust correlation to fish length than otolith width (Dehghani et al., 2016). Our results yielded very similar r2 values between fish measurements and otolith length (TL/SL to OL) and width (TL/SL to OW).
Unlike coastal species, myctophids are challenging to sample adequately (Saunders et al., 2020). Studies on mesopelagic fishes require larger and more expensive research vessels than those typically used in coastal surveys, which limits sampling opportunities and, consequently, data availability. Regression parameters are also provided for D. hudsoni from Southern Africa (Smale and Watson, 2024), D. perspicillatus from the North Atlantic Ocean (Quigley et al., 2023), H. hygomii from the Mediterranean Sea (Battaglia et al., 2015), and N. resplendens from the Canary Islands (Sarmiento-Lezcano et al., 2018). Otolith images are additionally available in Battaglia et al. (2015), Giaretta et al. (2017), Haimovici et al. (2024), Lombarte et al. (2006), Quigley et al. (2023), and Smale and Watson (2024), which provide scanning electron microscope (SEM) sagitta images.
Based on the coefficient of determination, both OL and OW proved to be good predictors of SL and TL for all Myctophidae species, except for L. guentheri. Considering the adequate size range and sample number for L. guentheri, it is necessary to test other otolith attributes, such as thickness or weight, as proxies for fish length reconstruction since the rate at which the otolith increases in length and width may vary among species. It is also recommended that future studies increase the N. resplendens data across its full-size range to produce more robust and accurate relationships. Along with the data of Madureira et al. (2005), our results expand the current knowledge about mesopelagic fishes in the Southwestern Atlantic Ocean and provide valuable information about the relationship between sagitta and fish size for myctophids captured on the continental margin of southeastern Brazil.
DATA AVAILABILITY STATEMENT
All data are available from the corresponding author upon reasonable request.
SUPPLEMENTARY MATERIAL
No Supplementary Material is available.
ACKNOWLEDGMENTS
The authors express their gratitude to all the team members involved in the REVIZEE Program, especially to Senior Professor Carmen Lucia del Bianco Rossi-Wongtschowski for her distinguished contributions to Ichthyology and fisheries science, as a researcher, a woman, and the founder of the Collection of Marine Fish Otoliths from the Southeast-South Region of Brazil (COSS-Brasil). We also thank the ColBIO (Coleção Biológica Edmundo Ferraz Nonato, IOUSP) for the current curation of COSS-Brasil.
REFERENCES
-
Agiadi, K., Nawrot, R., Albano, P. G., Koskeridou, E. & Zuschin, M. 2022. Potential and limitations of applying the mean temperature approach to fossil otolith assemblages. Environmental Biology of Fishes, 105, 1269-1286. DOI: https://doi.org/10.1007/s10641-022-01252-6
» https://doi.org/10.1007/s10641-022-01252-6 -
Agiadi, K., Quillévéré, F., Nawrot, R., Sommeville, T., Coll, M., Koskeridou, E., Fietzke, J. & Zuschin, M. 2023. Palaeontological evidence for community-level decrease in mesopelagic fish size during Pleistocene climate warming in the eastern Mediterranean. Proceedings of the Royal Society Biological Sciences, 209(1990), 29020221994. DOI: https://doi.org/10.1098/rspb.2022.1994
» https://doi.org/10.1098/rspb.2022.1994 -
Anderson, T. R., Martin, A. P., Lampitt, R. S., Trueman, C. N., Henson, S. A. & Mayor, D. J. 2019. Quantifying carbon fluxes from primary production to mesopelagic fish using a simple food web model. ICES Journal of Marine Sciences, 76(3), 690-701. DOI: https://doi.org/10.1093/icesjms/fsx234
» https://doi.org/10.1093/icesjms/fsx234 -
Battaglia, P., Malara, D., Ammendolia, G., Romeo, T. & Andaloro, F. 2015. Relationship between otolith size and fish length in some mesopelagic teleosts (Myctophidae, Paralepididae, Phosichthyidae and Stomiidae). Journal of Fish Biology, 87(3), 774-782. DOI: https://doi.org/10.1111/jfb.12744
» https://doi.org/10.1111/jfb.12744 -
Braga, A. C., Costa, P. A. S., Martins, A. S., Olavo, G. & Nunan, G. W. 2014. Lanternfish (Myctophidae) from eastern Brazil, southwest Atlantic Ocean. Latin American Journal of Aquatic Research, 42(1), 1, 245-257. DOI: https://doi.org/10.3856/vol42-issue1-fulltext-20
» https://doi.org/10.3856/vol42-issue1-fulltext-20 - Bonecker, A. C. T., Namiki, C. A. P., Castro, M. S. & Campos, P. N. 2014. Catálogo dos estágios iniciais do desenvolvimento dos peixes da bacia de Campos. Curitiba, Sociedade Brasileira de Zoologia.
-
Byrd, B. L., Hohn, A. A. & Krause, J. R. 2020. Using the otolith sulcus to aid in prey identification and improve estimates of prey size in diet studies of a piscivorous predator. Ecology and Evolution, 10(8), 3584-3604. DOI: https://doi.org/10.1002/ece3.6085
» https://doi.org/10.1002/ece3.6085 -
Dehghani, M., Kamrani, E., Salarpouri, A. & Sharifian, S. 2016. Otolith dimensions (length, width), otolith weight and fish length of Sardinella sindensis (Day, 1878), as index for environmental studies, Persian Gulf, Iran. Marine Biodiversity Records, 9(44), 44. DOI: https://doi.org/10.1186/s41200-016-0039-0
» https://doi.org/10.1186/s41200-016-0039-0 -
Giaretta, M. B.; Siliprandi, C. C.; Santificetur, C.; Brenha-Nunes, M. R.; Conversani, V. R. M.; Rossi-Wongtschowski, C. L. D. B. 2017. Atlas of marine bony fish otoliths (sagittae) of Southeastern-Southern Brazil Part VI: Albuliformes, Anguiliformes, Osmeriformes, Stomiiformes, Aulopiformes, Myctophiformes, Ophidiiformes, Polimixiiformes, Batrachoidiformes and Lophiformes. Brazilian Journal of Oceanography, 65(2), 258-308. DOI: https://doi.org/10.1590/S1679-87592017133806502
» https://doi.org/10.1590/S1679-87592017133806502 -
Haimovici, M., Rodrigues, L. S., Lucato, S. H. B., Freire, M. A., Fischer, L. G. & Cardoso, L. G. 2024. Otolith atlas for marine fishes of the southwestern Atlantic occurring along southern Brazil (28ºS-34ºS). Marine and Fishery Sciences, 37(1), 1, 53-207. DOI: https://doi.org/10.47193/mafis.3712024010101
» https://doi.org/10.47193/mafis.3712024010101 -
Hidalgo, M. & Browman, H. I. 2019. Developing the knowledge base needed to sustainably manage mesopelagic resources. ICES Journal of Marine Sciences , 76(3), 609-615. DOI: https://doi.org/10.1093/icesjms/fsz067
» https://doi.org/10.1093/icesjms/fsz067 -
Katsuragawa, M., Dias, J. F., Harari, J., Namiki, C. & Zani-Teixeira, M. L. 2014. Patterns in larval fish assemblages under the influence of the Brazil current. Continental Shelf Research, 89, 103-117. DOI: https://doi.org/10.1016/j.csr.2014.04.024
» https://doi.org/10.1016/j.csr.2014.04.024 -
Lin, C.-H., Lin, J.-S., Chen, K.-S., Chen, M.-H., Chen, C.-Y., Chang, C.-W. 2020. Feeding habits of Bigeye Tuna (Thunnus obesus) in the western Indian Ocean reveal a size-related shift in its fine-scale piscivorous diet. Frontiers in Marine Science, 7, 582571. DOI: https://doi.org/10.3389/fmars.2020.582571
» https://doi.org/10.3389/fmars.2020.582571 -
Lombarte, A., Chic, Ò., Parisi-Baradad, V., Olivella, R., Piera, J. & García-Ladona, E. 2006. A web-based environment for shape analysis of fish otoliths. The AFORO database. Scientia Marina, 70(1), 147-152. DOI: https://doi.org/10.3989/scimar.2006.70n1147
» https://doi.org/10.3989/scimar.2006.70n1147 - Madureira, L. S. P., Vasconcellos, M. C., Weigert, S. C., Habiaga, R. P., Pinho, M. P., Ferreira, C. S., Duvoisin, A. C., Soares, C. F. & Bruno, M. A. 2005. Distribuição, abundância e interações ambientais de espécies pelágicas na região sudeste-sul do Brasil, entre o cabo de São Tomé (RJ) e o Chuí (RS). In: Madureira, L. S. P. & Rossi-Wongtschowski, C. L. B. (Ed.). Prospecção de recursos pesqueiros pelágicos na Zona Econômica Exclusiva da Região Sudeste-Sul do Brasil: hidroacústica e biomassa (pp. 63-143). São Paulo: Instituto Oceanográfico - USP.
-
Martins, J. R., Mincarone, M. M., Bertrand, A., Artana, C., Lucena-Frédou, F., Koch-Larrouy, A., Lima, R. S. & Eduardo, L. N. 2025. Influence of the Amazon River plume on the biodiversity and assemblage structure of lanternfishes (Myctophidae). Deep-Sea Research Part I: Oceanographic Research Papers, 225, 104572. DOI: https://doi.org/10.1016/j.dsr.2025.104572
» https://doi.org/10.1016/j.dsr.2025.104572 -
Olivar, M. P., Bode, A., López-Pérez, C., Hulley, P. A. & Hernández-León, S. 2018. Trophic position of lanternfishes (Pisces: Myctophidae) of the tropical and equatorial Atlantic estimated using stable isotopes. ICES Journal of Marine Science, 76(3), 649-661. DOI: https://doi.org/10.1093/icesjms/fsx243
» https://doi.org/10.1093/icesjms/fsx243 -
Quigley, L. A., Caiger, P. E., Govindarajan, A. F., McMonagle, H., Jech, J. M., Lavery, A. C., Sosik, H. M. & Llopiz, J. K. 2023. Otolith characterization and integrative species identification of adult mesopelagic fishes from the western North Atlantic Ocean. Frontiers in Marine Science , 10, 1217779. DOI: https://doi.org/10.3389/fmars.2023.1217779
» https://doi.org/10.3389/fmars.2023.1217779 -
Rasband, W. S. 2018. ImageJ, U.S. National Institute of Health, Bethesda, Maryland, USA. Available from: Available from: https://imagej.net/ij/ Access date: 2026 Feb. 12.
» https://imagej.net/ij/ -
Rintz, C. L., Koubbi, P., Ramiro-Sánchez, B., Azarian, C., Caccavo, J. A., Cotté, C., Goberville, E., Godet, C., Hulley, P. A., Le Goff, R., Leprieur, F., Robuchon, M., Serandour, B. & Leroy, B. 2025. Biogeographical regions and climate change: lanternfishes shed light on the role of climatic barriers in the Southern Ocean. Global Change Biology, 31(6), e70256. DOI: https://doi.org/10.1111/gcb.70256
» https://doi.org/10.1111/gcb.70256 -
Rossi-Wongtschowski, C. L. D. B., Chalom, A., Siliprandi, C. C., Brenha-Nunes, M. R., Conversani, V. R. M., Santificetur, C. & Giaretta, M. B. 2016. COSS-Brasil: Coleção de Otólitos de Peixes Teleósteos da Região Sudeste-Sul do Brasil. Instituto Oceanográfico da Universidade de São Paulo. Available from: Available from: http://www.usp.br/cossbrasil Access date: 2026 Jan. 30.
» http://www.usp.br/cossbrasil -
Saba, G. K., Burd, A. B., Dunne, J. P., Hernández-León, S., Martin, A. H., Rose, K. A., Salisbury, J., Steinberg, D. K., Trueman, C. N., Wilson, R. W. & Wilson, S. E. 2021. Toward a better understanding of fish-based contribution to ocean carbon flux. Limnology and Oceanography, 66(5), 1639-1664. DOI: https://doi.org/10.1002/lno.11709
» https://doi.org/10.1002/lno.11709 -
Sarmiento-Lezcano, A.-N., Triay-Portella, R., Castro, J. J., Rubio-Rodríguez, U. & Pajuelo, J. G. 2018. Age-based life-history parameters of the mesopelagic fish Notoscopelus resplendens (Richardson, 1845) in the Central Eastern Atlantic. Fisheries Research, 204, 412-423. DOI: https://doi.org/10.1016/j.fishres.2018.03.016
» https://doi.org/10.1016/j.fishres.2018.03.016 -
Saunders, R. A., Lourenço, S., Vieira, R. P., Collins, M. A. & Xavier, J. C. 2020. Length-weight and otolith size to standard length relationships in 12 species of Southern Ocean Myctophidae: a tool for predator diet studies. Journal of Applied Ichthyology, 37(1), 140-144. DOI: https://doi.org/10.1111/jai.14126
» https://doi.org/10.1111/jai.14126 -
Schwarzhans, W. & Carnevale, G. 2021. The rise to dominance of lanternfishes (Teleostei: Myctophidae) in the oceanic ecosystems: a paleontological perspective. Paleobiology, 47(3), 446-463. DOI: https://doi.org/10.1017/pab.2021.2
» https://doi.org/10.1017/pab.2021.2 -
Smale, M. J. & Watson, G. 2024. Otoliths atlas of marine fishes of Southern Africa and adjacent oceans. Makhanda, NISC. DOI: https://doi.org/10.5962/bhl.title.141860
» https://doi.org/10.5962/bhl.title.141860 -
Weigert, S. C. & Madureira, L. S. P. 2011. Registros acústicos biológicos detectados na zona econômica exclusiva da região Nordeste do Brasil - uma classificação em ecotipos funcionais. Atlântica, 33(1), 15-32. DOI: https://doi.org/10.5088/atl%C3%A2ntica.v33i1.2676
» https://doi.org/10.5088/atl%C3%A2ntica.v33i1.2676 -
Zanchin, V. R., Temperoni, B., Acha, E. M., Buratti, C. C. & Alemany, D. 2025. Lanternfish (Myctophidae) distribution and diversity patterns in the Southwestern Atlantic Ocean. Deep Sea Research Part I: Oceanographic Research Papers, 222, 101518. DOI: https://doi.org/10.1016/j.dsr.2025.104518
» https://doi.org/10.1016/j.dsr.2025.104518
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AI USE STATEMENT
Artificial intelligence tools (OpenAI) were used exclusively to refine the English language of this manuscript. The content was carefully reviewed by the authors to ensure consistency and correctness, and the authors are fully responsible for the final version of the manuscript.
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FUNDING
This study was financed by the São Paulo Research Foundation (FAPESP), Brazil. Process Numbers #2023/09027-0 and #2020/14356-5.
