Species Description: The frillfin goby, Bathygobius soporator, is one of several species in the IRL belonging to the family Gobiidae. Members of this family are mostly small, demersal (bottom-associated) fishes with separate dorsal fins. The pelvic fins of gobiids have one spine and five rays, are close together, and are usually connected via a disk-shaped membrane called a frenum (Robins & Ray 1986). Numbers of fin rays, scales and head pores, as well as differences in color and pattern, are important characteristics used to distinguish among species.
The body color of B. soporator is variable, changing with habitat type to shades of green, brown, tan, cream or black (Tavolga 1950b). Most individuals are dark brown, bearing a series of five black saddles across the back. The saddle below the 1st dorsal fin is the broadest (Robins & Ray 1986).
The common name of this species is derived from the upper rays of the pectoral fin, which are free, branched and frill-like.
Potentially Misidentified Species: Comprised of over 2,000 species, Gobiidae is possibly the largest family of fishes (Robins & Ray 1986), several of which are found in the IRL. Of these, the species most closely related to B. soporator is the notchtongue goby, B. curacao. Similar in appearance to the frillfin goby, B. curacao is characterized by a tan stripe on the 2nd dorsal and anal fins, especially in males (Robins & Ray 1986). As the name implies, the tongue is more deeply notched than the frillfin goby. Like B. soporator, the 1st dorsal fin bears six spines, but the pectoral fin rays range from 15-18, and lateral line scales from 31-34. Individuals are found in tide pools, around mangroves and in sheltered seagrass beds.
Regional Occurrence & Habitat Preference: Comprised of over 2,000 species, Gobiidae is one of the largest families of fishes (Robins & Ray 1986), with several representatives in the IRL. Of these, the species most closely related to B. soporator is the notchtongue goby, B. curacao. Similar in appearance to the frillfin goby, B. curacao is characterized by a tan stripe on the 2nd dorsal and anal fins, especially in males (Robins & Ray 1986). As the name implies, the tongue is more deeply notched than the frillfin goby. Like B. soporator, the 1st dorsal fin bears six spines, but the pectoral fin rays range from 15-18, and lateral line scales from 31-34. Individuals are found in tide pools, around mangroves and in sheltered seagrass beds.
IRL Distribution: The frillfin goby occurs throughout the IRL, but is likely most abundant around inlets at jetties, seawalls, tide pools and hardbottom areas. Individuals have been collected from the Fort Pierce and Sebastian Inlets (Sweat, pers. obs.).
Age, Size, Lifespan: The maximum age of B. soporator is unknown, and the lifespan can vary with food availability and environmental factors. The average reported size for the frillfin goby is 7.5 cm (Robins & Ray 1986), though specimens collected from the Bahamas ranged in length from 2.0 to 8.8 cm (Tavolga 1950).
Reproduction: Following internal fertilization, the female goby lays eggs on a sheltered hard surface, commonly the interior of empty conch shells (Tavolga 1958a). Presumably, as with other gobiid species, the male fertilizes eggs of several females. Each mate lays her eggs in the same location to form one large cluster of 800 to 1,000 eggs (Tavolga 1958a) comprised of a few to several clutches. This egg cluster is protected by the parental male until hatching occurs. Unlike non-breeding males and females, parental males are fiercely territorial, chasing intruders and never venturing more than a few feet from the nest (Tavolga 1958a).
Embryology: When first laid, the eggs of the frillfin goby are ovoid with a thin, smooth chorion (outer layer) (Tavolga 1958a). As mentioned above, eggs are attached to hard substrata like conch shells, usually on the underside surface. After 2-3 minutes, the chorion elongates, with the egg remaining in the center. Finally, after 15-20 minutes the chorion expands fully and alters its shape to hug the developing embryo, resembling a sarcophagus. The embryos develop in a head-down position most likely to facilitate hatching. Those that were manipulated to an upright orientation could not break through the egg membranes and died within several hours (Tavolga 1958a). Embryos maintained between 27 and 29°C develop in about 100 hours, passing through 22 stages before hatching. Larvae are approximately 2.6 to 2.7 mm long and feed on protozoa and microalgae. When a suitable habitat is located, the larvae settle to the bottom near adult B. soporator. Field collected post-larvae of the frillfin goby measure about 7.5 mm in length.
Temperature: The tropical to subtropical range of the frillfin goby suggests that the species prefers warm, coastal waters. Larvae of B. soporator have been successfully reared in captivity at temperatures of 24 to 29°C (Tavolga 1950a, 1950b).
Trophic Mode: The dietary preferences of B. soporator
are poorly reported. However, the demersal lifestyle of the
goby suggests that it may feed upon small invertebrates, fishes
and detritus from rocky intertidal areas.
Predators: Information regarding predators of B. soporator is scarce. However, this goby is likely preyed upon by a variety of larger fishes and crustaceans. Cannibalism of egg clutches by parental males has been reported when the nests were disturbed (Tavolga 1950a). The planktonic larvae of the frillfin goby are consumed by a variety of organisms.
Associated Species: No known obligate associations exist for B. soporator. However, frillfin gobies are associated with several organisms common to rocky intertidal areas, hardbottom communities and tidepools.
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