The rough silverside (Membras martinica) belongs to the order Atheriniformes, family Atherinopsidae. This species is found in the Western Atlantic, from Long Island, New York, to the Terminos Lagoon in Campeche, Mexico. However, here we report the first sighting of adult M. martinica in the continental Caribbean, specifically in the Nichupté-Bojórquez lagoon system of the Mexican Caribbean.

• Continental Caribbean • Habitat • Lagoon System • Reef Fishes

Navarro TD, Va?zquez JAC (2026) Adult Specimen of Membras martinica (Atherinopterygii: Atherinopsidae): New Record Extending its Range into the Mexican Caribbean. Ann Aquac Res 8(1): 1051.

Out of almost 11,593 kilometers of Mexico’s coastline, about one-third consists of coastal lagoons [1]. Coastal lagoons are inland water bodies separated from the ocean by a barrier but still connected to it at least sometimes [2]. The seawater in these lagoons is usually mixed with freshwater from river mouths, runoff, or rainfall, which affects their ecology [3]. These complex and highly productive environments provide goods and services— such as fisheries, tourism, and aesthetic and cultural values—that support the well-being of many people.

Coastal lagoons are ecosystems that feature several unique habitats interconnected by chemical, physical, and biological factors [4]. They are commonly used by fish for spawning; in addition, these lagoons also serve as nurseries and feeding grounds. Because of the mixture of freshwater and seawater, they also function as pathways for diadromous migrations [4,5]. Furthermore, they provide habitats for species that live in coastal lagoons throughout their entire development [6].

Two decades ago [7], documented 563 fish species in Mexico’s estuarine and lagoon systems; among these,the order Atheriniformes included seven genera and 15 species [8]. A more recent study of the Mexican Caribbean recorded 577 fish species, including 5 species of the order Atheriniformes across 4 genera [9]. The Nichupté Bojórquez lagoon system is located in the northeastern corner of the Yucatan Peninsula, next to the city of Cancun. It is one of Mexico’s top tourist destinations and a developing area [10]. Reséndez-Medina [11], reported 37 fish species in this lagoon system; since then, only one additional species has been found [7-12]. (None of the 38 species recorded for this lagoon system belongs to the order Atheriniformes. This likely results from limited studies to fully document the fish diversity in the Nichupté Bojórquez lagoon system.

The Atherinopsidae family of silverside fish, Atheriniformes, comprises 13 genera and 110 species. Nearly 50 species live entirely in freshwater, while about 58 species are primarily found in seawater or brackish water [13].

The rough silverside Membras martinica (Valenciennes 1835) was described from Martinique in the Caribbean Sea [14], and is considered to have a distribution in the Western-Central Atlantic that extends from Long Island, New York, to the Terminos Lagoon, Campeche, Mexico [15]. However, most M. martinica specimens are found along the northern coast of the Gulf of Mexico near the southern United States [16-24], and in the Mexican states of Tamaulipas and Veracruz [7-26]. In addition to the initial description of the species from Martinique, it has been documented only once in the Caribbean Sea by Ramjohn [26], with one specimen found in Little Rocky Bay, Trinidad and Tobago.

The Gulf of Mexico’s inland sea and the Mexican Caribbean share estuarine lagoon and riverine areas. Given the existing connectivity among coastal aquatic systems, fish species may expand their ranges across Caribbean regions. Little is known about the natural history, biology, and population genetic structure of the rough silverside. Dispersal ability strongly influences genetic connectivity in marine species [27]. The M. Martinica population registry in the Mexican Caribbean provides an ideal system for studying gene flow and isolation-by-distance across geographic scales.

A distribution map of M. martinica in the western Atlantic, including the Gulf of Mexico and the Greater Caribbean, was compiled from reported larval and adult stages in publicly available databases, including FishBase [28], the Smithsonian Tropical Research Institute [29], the Integrated Taxonomic Information System [30], and the World Register of Marine Species [28], along with the adult registry from this study (Figure 1).

Figure 1 Distribution map of Membras martinica in the western Atlantic. Previous records (?) (OBIS, 2018), Type locality (?), ichthyoplankton records (?), and a new record (?) for the species in the Mexican Caribbean.

In July 2017, an adult specimen of M. martinica was collected from the Nichupté-Bojórquez lagoon system, near the Nichupté Mangrove Flora and Fauna Protection Area, at the coordinates 21°8’41.89”N, 86°48’0.65”W (Figure 1). The fish was caught using a 45-meter-long by 1.7-meter-deep seine net with a mesh size of 2.5 cm, except for the bag, which had a mesh size of 1.43 cm. It was transported to the laboratory and fixed in 10% neutral buffered formalin. Afterward, it was washed with water for 48 hours and then preserved in 70% ethanol. Species identification was performed using several identification keys to ensure accuracy [7-31]. The specimen is stored in the Ichthyological Collection of the Ecology and Biodiversity of Aquatic Organisms Laboratory at the Centro de Investigación Científica de Yucatán, with catalog number CIC-7231 and scientific collection permit (SCP) number F00.9.DAPFFMN.-001/2017.

The following diagnostic features distinguish M. martinica from related species (Figure 2):

Figure 2 Membras martinica collected in Nichupté-Bojórquez lagoon, Cancun, Mexico. A) A collected organism, lateral view; B) scales on sides with fringed rear edges.

1) a slim, elongated, compressed body; 2) four large, square-shaped sensory pits on top of the snout; 3) a strongly extendable upper jaw; 4) the first dorsal-fin ray originates well before the origin of the anal fin; 5) a pair of dark spots on the back; 6) the anus opening is closer to the anal fin origin than to the pelvic fin base; 7) flank scales have fringed rear edges; 8) dorsal and anal fin bases are scaled; 9) the body cavity is located anterior to the anus; 10) the upper body is bright yellow to sea-green, speckled or cross-hatched with dark pigment, the lower body is silvery, with a silver flank stripe; 11) the lateral line width is approximately the same as the diameter of the eye.

This manuscript documents the first sighting of an adult rough silverside, M. martinica, in the continental Caribbean, specifically within the Mexican Caribbean’s Nichupté-Bojórquez lagoon system. Previously, the species had only been recorded as ichthyoplankton at the larval stage [1-32]. The original range of M. martinica includes parts of Mexico (Tamaulipas and Veracruz) and the United States (Alabama, Delaware, Florida, Georgia, Louisiana, Maryland, Mississippi, New Jersey, North Carolina, South Carolina, Texas, and Virginia) [33]. Due to limited data on the species’ biological distribution in the Caribbean and infrequent adult sightings in the area, it remains uncertain whether M. martinica from the Gulf or the Mexican Caribbean is native.

Although it has been considered invasive in the Gulf of Mexico [34], the lack of current data underscores the need for a phylogeographic analysis that includes haplotypes from both the Caribbean and the Gulf (including Martinique, suspected to be the origin). Such an analysis could clarify whether M. martinica should be considered invasive. Further research on connectivity between Gulf and Caribbean populations could support these hypotheses. Although existing evidence suggests that the species currently poses a low risk of hybridization producing fertile offspring or causing major ecological disruptions in the short- to medium-term (5-20 years), the discovery of adult M. martinica in the Nichupté-Bojórquez lagoon system could heighten this risk.

Nevertheless, the species also serves as prey for key predators in the area and plays a vital role in the lagoon’s trophic dynamics. In this study, M. martinica was found alongside a school of hardhead silverside, Atherinomorus stipes, which has a translucent green dorsal surface, a prominent silver stripe along the lateral line, and a body shape and coloration similar to those of M. martinica. However, they are distinguished at the species level by specific taxonomic traits, including a large eye (twice the snout length), a broad head (63% of head length), a non extendable upper jaw that extends beyond the front of the eye, a front (premaxilla) bone with a narrow, pointed rear end (not expanded), small, simple teeth arranged in narrow bands on the jaws, small outward-pointing teeth at the center of the lower lip, a small projection at the rear of the lower jaw, an anus located well before the anal fin, and a sheath of scales at the bases of the dorsal, anal, and pectoral fins. 

Therefore, the hypothesis that the lack of records of adult rough silversides at other sites in the Mexican Caribbean is due to the species often being confused with the hardhead silverside because of their similar appearance should be interpreted with caution. Records of the species at the Museum of Comparative Zoology (MCZ, Harvard University) often require taxonomic revision to separate it from other species because of historical misidentifications. The Global Biodiversity Information Facility (GBIF) database shows a high concentration of shared records in the Gulf of Mexico and the Caribbean, where specimens of Membras and Atherinomorus overlap. A Field Guide to Atlantic Coast Fishes is often cited as the standard reference for distinguishing these species. Recent studies of Membras indicate morphological differences (geometric morphometrics) to avoid confusion between small and immature individuals of M. martinica [35].

Observations

The specimen was collected from the Nichupté Bojórquez lagoon system in Cancun, Quintana Roo, Mexico, located next to the Nichupté Mangrove Flora and Fauna Protection Area at coordinates 21°8’41.89”N, 86°48’0.65”W (Figure 1). It was caught with a 45 m long, 1.7 m deep seine net with a 2.5 cm mesh size, except for the bag, which has a 1.43 cm mesh size. The specimen is stored in the Ichthyological Collection of the Ecology and Biodiversity of Aquatic Organisms Laboratory at the Centro de Investigación Científica de Yucatán, with catalog number CIC-7231 and collection permit number F00.9.DAPFFMN.-001/2017.

Identification

The collected organism, the silverside M. martinica, is an adult specimen. The manuscript’s results highlight specific morphological features that distinguish it from other similar species, including the inland silverside (Menidia beryllina). We have reviewed references and photos from FishBase, the Smithsonian Tropical Research Institute, the Integrated Taxonomic Information System, and the World Register of Marine Species, which allowed us to confirm the correct species identification.

The manuscript documents the first record of adult rough silverside (M. martinica) in the continental Caribbean, from the Nichupté-Bojórquez lagoon system (Mexican Caribbean). Before this study, the species had been reported only as larval ichthyoplankton. The collection site is 1-2 meters deep, with an average salinity of 30.1 ppt. It features mangrove fringes, with Rhizophora as the dominant species. The mangrove systems at this site were recently restored and are monitored as part of the mangrove-protected area’s management program [5-39]. The area also hosts Thalassia testudinum, which covers small sandy flats. Despite comprehensive sampling— seining at seven sites across three climatic seasons— the study recorded only one occurrence of the species, suggesting that M. martinica is rare in this region and possibly explaining the lack of previous records in the Mexican Caribbean. M. martinica was collected alongside a shoal of hardhead silversides, Atherinomorus stipes, which have a translucent green dorsal surface, a prominent silver stripe along the lateral line, and a body shape similar to M. martinica but a different taxonomic placement. The absence of adult rough silversides in other parts of the Mexican Caribbean may be due to confusion with Atherinomorus stipes based on overall appearance. Future efforts to collect molecular samples are important, as they could provide crucial information about genetic diversity and relationships within the family.

This work was supported by the Centro de Investigación Científica de Yucatán, A.C., and was made possible by collection permit number F00.9.DAPFFMN.-001/2017. The first author thanks the National Council of Science and Technology (CONACYT) for financial support (Scholarship number 435362). We thank Vincent Smith and Cecilia Hernández Zepeda for their English-language review of the manuscript, and Jorge Carlos Peniche Pérez for his technical assistance. We also thank the personnel at the Nichupté Mangrove Flora and Fauna Protection Area, Isla Mujeres West Coast, Punta Cancún, and Punta Nizuc National Park for their invaluable support.

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