June Fish of the Month: Fat Sleeper Dormitator maculatus

Dr. Geoffrey Smith

NWFSC Biology Instructor

The Fat Sleeper is a fish that is relatively common throughout Florida, including the panhandle. It is found in brackish waters and freshwater creeks and rivers connected to estuaries from North Carolina south through the Gulf of Mexico to Brazil (Figure 1). However, there is evidence that populations found in the Caribbean and the southern portion of its range may actually consist of several very similar, closely related species. This species commonly reaches 5-6 inches in length, with maximum sizes of up to 27 inches being reported. However, some of this variation in size may be related to the possibility that this is actually several different species.

The Fat Sleeper is a member of the Family Eleotridae, named after the Greek word referring to a specific fish species of this family found in the Nile River. The fishes in this family are commonly known as sleepers due to their tendency to lie on the bottom, and they were previously grouped with the gobies. However, the sleepers do not have the fused pelvic fins that are generally characteristic of the gobies (see some of our previous Fish of the Month posts). The genus name Dormitator is derived from the Latin dormire which means to sleep, again referring to the fact that these fish often sit on the bottom, and the species name maculatus is derived from the Latin maculare meaning to make spotted, referring to the spotted or blotchy appearance of this species.

Overall, Fat Sleepers are generally a brown to black background color depending on water and bottom coloration (Figure 2). There are a number of oblique bars formed from spots on the body, a large blue to black blotch above the base of the pectoral (side of body) fins, and several darker stripes on the head. The dorsal (top of body) and anal (bottom rear) fins may also have some red to orange coloration, especially in spawning males (Figure 2).

The Fat Sleeper is often referred to as a marine invader in freshwater systems, since the adults are generally found in lower salinity brackish to fresh waters (often miles from the ocean) while it is thought that the larvae need to develop in marine waters prior to moving into lower salinity waters. There is not much know about the overall biology of this species in terms of maximum age or reproduction, but they can survive for up to a decade or more and their eggs are laid on rocks, vegetation, etc. before hatching, when it is suspected that the larvae are carried into marine waters by tides prior to migrating back into lower salinity waters.

In the US, there is generally little harvest of this species and that harvest is generally for the aquarium trade where they are one of several species that are sold as Jade Gobies. However, in the southern part of its range, there is harvest not only for the aquarium trade, but also as food both for local subsistence and sold as a local delicacy.