Dr. Geoffrey Smith
NWFSC Biology Instructor
This month I’ll be highlighting a relatively ubiquitous but not well known species found in most estuarine systems along the Atlantic coast and throughout the Gulf of Mexico (Figure 1). The Clown Goby is a relatively small species, reaching a maximum size of about three inches (hence Microgobius, which roughly translates to small goby). However, they have a relatively large mouth, especially males, for their size (hence gulosus or large mouthed). They are found over bare sandy and muddy substrates, as well as within submerged aquatic vegetation in estuaries. Their large mouths are used to excavate the sediment burrows that they often reside in, particularly while they are mating and rearing eggs. The Clown Goby is very tolerant of a wide range of salinities and can be found in freshwater springs and rivers directly connected to ocean water but they can also be found throughout tidal creeks and along the shorelines of larger rivers and bays. Like all gobies, the Clown Goby has its pelvic fins (the paired fin on the bottom of the body toward the front of the fish) modified into a suction cup like structure that allows them to perch on rock, logs, etc. and remain in place in the presence of waves or current. This species is sexually dimorphic, meaning that there are clear differences in the body form or coloration of males and females. Male Clown Gobies have very long filaments extending off of three of their dorsal fin (fin on the top of the body) spines (Figure 2). The overall body color of both males and females is gray to tan with some darker spots (Figures 2 and 3). In addition, males have iridescent white to light blue markings on their face, similar to face paint on a clown, and iridescent orange and blue along the margins of the dorsal, anal (fin on the bottom rear of the fish), and caudal (tail) fins (Figure 2). These bright colors are used to attract females. They also use a combination of these bright colors and mouth sparring (Figure 4) to ward off other males in their territories. Other than a very limited harvest for the aquarium trade, Clown Gobies do not have a direct impact on the economy. However, they are regularly consumed by juvenile sportfish, such as Common Snook, Red Drum, and Spotted Seatrout that use tidal creeks, marshes, and shallow seagrass beds as nursery areas. And these sportfish do have major, direct impacts on local economies all along the Gulf and Atlantic coasts.
Figure 1: Distribution of Clown Goby within the Gulf of Mexico and along the southern Atlantic coast, note their range extends northward to Maryland (https://biogeodb.stri.si.edu/caribbean).
Figure 2: Typical coloration of a male Clown Goby, note the 3 extended dorsal spine filaments, bright face markings, and bright fin margins. Photos by G. Smith.
Figure 3: Typical coloration of a female Clown Goby, note that lack of extended dorsal spine filaments, bright face markings, and bright fin margins. Photo credit: J. Van Tassell and D. Robertson (https://biogeodb.stri.si.edu/caribbean).
Figure 4: Mouth sparring (gaping contest) between two males. One male was isolated in an acrylic box to facilitate photography. Photo credit: Ana Gaisiner (Gaisiner, A. 2005. Parental care and reproductive behavior of the clown goby, Microgobius gulosus, with observations on predator interactions. Environmental Biology of Fishes 73: 341-356.
