Elacatinus is a genus of small marine gobies, often known collectively as the neon gobies. Although only one species, E. oceanops, is technically the "neon goby," because of their similar appearance, other members of the genus are generally labeled neon gobies, as well. Except for a single East Pacific species, all reside in warmer parts of the West Atlantic, including the Caribbean and Gulf of Mexico. They are known for engaging in symbiosis with other marine creatures by providing them cleaning service that consists of getting rid of ectoparasites on their bodies. In return, Elacatinus species obtain their primary source of food, ectoparasites.
Neon gobies are very small, torpedo-shaped fish. Although sizes vary slightly by species, they are generally about 2.5 cm (0.98 in) long.[2] They have dark bodies with iridescent stripes running from the tip of the nose to the base of the caudal fin. The color of the stripes varies by species. Like all gobies, their dorsal fin is split in two, the anterior dorsal fin being rounded like that of a clownfish and the posterior dorsal fin being relatively flat. The anal fin lines up with the posterior dorsal fin and is of similar shape. The pectoral fins are nearly circular, and, like all other fins, transparent.[2]
Except for the East Pacific E. puncticulatus, all gobies of the genus Elacatinus reside in warmer parts of the western Atlantic, ranging from Florida and Bermuda, through the Bahamas, Caribbean and Gulf of Mexico to the coasts of Central America and northern South America (south to Brazil).[3] Among the species is E. oceanops that resides in the Caribbean Sea, the Florida Keys and the Bahama Islands. They have been found along the northern Yucatan Peninsula.[4]
Elacatinus are generally carnivorous, with their primary diet consisting of ectoparasites on skins, fins, mouth and gill chambers of their clients.[5] Depending on their ecological circumstances, they may also feed on zooplankton and non-parasitic copepods.[6] Although they are carnivorous, Elacatinus occasionally consume algae and other plants as secondary food source.[5]
Some species of gobies exhibit gonochorism and protogynous hermaphroditism, including bidirectional sex reversal.[7] Protogyny refers to a category of hermaphroditism where female organs develop or mature before the appearance of male product.[8] In most males of Tellostei gobiidae, this characteristic is observed.[9]Among those in the genus Elacatinus, protogyny is observed in E. illecebrosus.[10]Protogynous hermaphroditism in gobies consists of a male reproductive system with paired, secretory, accessory gonadal structures (AGSs) associated with the testis.[11]While the AGS is almost universally present in male gobies, protogynous females need to develop AGSs for sex reversal to take place. The AGSs develop from precursive tissues (pAGSs), in the form of bilateral, ventrally localized cell masses, located close to the junction of the ovarian lobes and the oviduct. At the time of sex change, it undergoes rapid growth and diverts to form the AGSs.[11] When pAGSs develop into AGSs, ovigerous tissue is also completely replaced by seminiferous lobules. However, the ovarian lumen remains even after the sex change, functioning as a common spermatozoa collection region that is continuous with the common genital sinus as free spermatozoa travels from seminiferous lobules into the gonadal lumen.[10]
Gonochorism refers to development or evolution of sex.[8] Gonochoric goby species normally do not possess pAGSs, but pAGSs are observed in E. illecebrosus and E. evelynae.[11] Specifically, the ovarian lobes of small-sized juvenile females of these species possess distinctive pAGSs that started to diminish and then disappeared as they approach adulthood.[11]