# Key silverside

The Key silverside (Menidia conchorum) is a species of fish in the family Atherinopsidae: Menidiinae. It is endemic to the Florida Keys.
The American Fisheries Society (2023) and Eschmeyer's Catalog of Fishes (2023) both verify Menidia conchorum as a distinct species. Research by authorities such as Robins and Ray (1986), Gilbert (1992), Conover et al. (2000), and Musick et al. (2000) supports its classification, establishing it as genetically and morphologically unique from related species. Population genetics studies (O'Leary et al., 2016) further confirm its status as a valid species, distinguishing it through genetic and morphological analyses.
Since the 1980s, Menidia conchorum populations have faced a significant decline, predominantly due to the rapid disappearance of their habitat in the salt-ponded waters of the lower Florida Keys and, more importantly, due to the effect of rising sea levels the Florida Fish and Wildlife Conservation Commission recently cataloged the species as threatened. The U.S. National Marine Fisheries Service has also identified the species as a Species of Concern.

## Species Description

Getter's 1981 survey, conducted in the late 1970s across the entire Florida Keys, established that the Key silverside exhibits a limited distribution, confined to the lagoonal and ponded waters of the Florida Keys. This unique and relatively rare habitat is home to a community of fishes, many of which are found exclusively in this location.
As the smallest known species in the genus Menidia, according to the Florida Fish and Wildlife Conservation Commission, female Key silversides can reach up to 58 mm in standard length, while males typically grow up to 50 mm. While it shares a close relationship (paraphyletic) with the Tidewater silverside (Menidia peninsulae), the Key silverside is distinguishable by its deeper body, yellow coloring, and habitat and range restrictions. Moreover, laboratory tests show it has a lower cold tolerance than its relatives.

## Conservation

The rise in sea level continues to inundate many of the larger salt ponds that have become well-flushed lagoons. These isolated, fragmented ponds serve as crucial lifelines for the species' survival. In the past, many such salt ponds and lagoons have been filled for development purposes, significantly reducing available habitats. This has resulted in the loss of numerous ponds, previously occupied sites, and ponded and lagoonal habitats.
If proactive interventions are not undertaken, the extinction of an endemic Florida Keys fish species—the Key silversides—may occur within the next decade (Getter, 2010).

## Conservation Designations

According to the Florida Fish and Wildlife Conservation Commission, following the research findings from the Key silverside Biological Review Group and subsequent discussions with other FWC fish experts, the staff recommends that the Key silverside (Menidia conchorum) be listed as a Threatened species. This recommendation is based on the fact that the species fulfills the listing criteria outlined in rule 68A-27.0012, F.A.C.

## Status Reviews

Dr. Chuck Getter, who has been studying the species since the 1970s for his doctoral dissertation (Ecology and survival of the Key silverside, Menidia conchorum, an atherinid fish endemic to the Florida Keys, Ph.D., University of Miami, Rosenstiel School of Marine and Atmospheric Sciences), is currently conducting further research on this species (Getter 2009, 2010). This ongoing work involves updating his initial study with new data in preparation for publication in 2025. Despite challenges, the Key silverside plays an irreplaceable role in its ecosystem. As one of the few species adapted to the fluctuating salinity and temperatures of the Florida Keys’ ponds and lagoons, it contributes to these unique habitats' biodiversity and ecological resilience. The Florida Fish and Wildlife Conservation Commission classifies the Key silverside as “Threatened,” recommending it be prioritized for conservation efforts. The preservation of this species is not just a matter of preventing extinction but also of maintaining the ecological integrity of the Florida Keys’ rare and fragile habitats.
Efforts to conserve the Key silverside align with broader conservation goals in the Florida Keys, where protecting unique species like M. conchorum is critical in the face of rising sea levels and other climate-related threats. The ongoing work by scientists and conservation organizations underscores the importance of proactive measures to protect this species, which, if successful, could serve as a model for preserving other threatened species in similarly vulnerable environments.