Bigmouth Sleeper, Gobiomorus dormitor
Bigmouth Sleeper, Gobiomorus dormitor. Fish caught from within the Sebastian Inlet, Micco, Florida, April 2019. Length: 26 cm (10 inches). Catch, photograph and identification courtesy of Ryan Crutchfield, Tampa, Florida.
Bigmouth Sleeper, Gobiomorus dormitor. Fish caught from within the Sebastian Inlet, Micco, Florida, March 2021. Length: 28 cm (11 inches). Catch, photograph and identification courtesy of Ben Cantrell, Sebastian, Florida.
Bigmouth Sleeper, Gobiomorus dormitor. Fish caught from within the Sebastian Inlet, Micco, Florida, April 2021. Length: 33 cm (13 inches). Catch, photograph and identification courtesy of Ben Cantrell, Sebastian, Florida.
Bigmouth Sleeper, Gobiomorus dormitor. Fish caught from a freshwater stream in Puerto Chomes, Costa Rica, March 2021. Length: 33 cm (13 inches). Catch, photograph and identification courtesy of Eli (obsessiveangling.wordpress.com).
The Bigmouth Sleeper, Gobiomorus dormitor, is a member of the Sleeper or Eleotridae Family, and is known in Mexico as guavina bocona. Globally, there are four species in the genus Gobiomorus, of which two are found in Mexican waters, one in the freshwater drainage systems of the Atlantic and one in the freshwater drainage system of the Pacific Ocean.
The Bigmouth Sleeper has an elongated cylindrical stout body that tapers toward the rear. They are dark brown to olive brown dorsally transitioning to tan to tan with yellow tints ventrally. They have several faint dark stripes on the gill cover, an oblique black bar across the rear half of the first dorsal fin and rows of spots on the caudal and second dorsal fins. Juveniles are more intensely colored than adults with a black stripe that runs from the snout through the eyes to the base of the caudal fin; their tail base has 3 black spots. Their head is broad and elongated with a blunt snout with a conical profile that is depressed above with small beady eyes on top with a large mouth with a projecting lower jaw that is equipped with several rows of small conical teeth on the jaws and the front of the roof of the mouth. Their anal fin has 1 spine and 8 to 10 rays; their caudal fin is broad and rounded; their first dorsal fin has 6 weak spines; their second dorsal fin has 1 spine and 9 rays; their pectoral fins have 16 or 17 rays and are broad and fan-like; and, their pelvic fins have 1 spine and 5 rays and are widely separated at the point of attachment. They have 14 to 17 gill rakers. Their body is covered with rough scales; their head has smooth scales. They do not have a lateral line.
The Bigmouth Sleeper is a demersal species found in clear freshwater rivers, often far upstream, over sand substrate within the current near cover in water temperature between 22oC (72oF) and 29oC (84oF) at elevations below 300 m (1,000 feet) at depths up to 5 m (16 feet). Their juveniles are found in shallow estuaries and brackish waters with salt levels between 0 and 13 ppt. They have the ability to move over land short distances. They reach a maximum of 90 cm (2 feet 11 inches) in length and 7.5 kg (16 lbs 8 oz). As of January 1, 2023, the International Game Fish Association world record stood at 2.03 kg (4 lbs 7 oz) with the fish caught in coastal waters off Costa Rica in March 2001. The adults are ambush predators that feed on small river shrimps and small fishes including cichlid fry. The juveniles consume insects. They rely on their cryptic coloration for both feeding and to avoid predation. For reproduction they are diadromous with the adults migrating from freshwater to the ocean to reproduce or they release their eggs and larvae such that they are taken by the currents into the ocean. The juveniles return to the fresh water environments and develop until they return to the ocean to reproduce. Because of this reproduction mode they are classified as environmentally sensitive and have been placed on the list of vulnerable organisms. The Bigmouth Sleeper is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.
The Bigmouth Sleeper is easily confused with the Guavina, Guavina guavina (all fins with yellow margins), the Large-scaled Spinycheek Sleeper, Eleotris amblyopsis (dark spot on upper pectoral base; body without lines or spots; large canines at the rear of mouth); and, the Small-scaled Spinycheek Sleeper, Eleotris pernigers (dark spot on upper pectoral base; large canines at the rear of mouth).
The Bigmouth Sleeper is found in all Mexican freshwater systems at elevations up to 300 m (1,000 feet) that drain into the Atlantic Ocean. They are more common in the tributaries the drain into the Southern Gulf of Mexico.
From a conservation perspective the Bigmouth Sleeper is currently considered to be of Least Concern with stable, widely distributed populations. They are fairly common in Mexican freshwater of the Atlantic Ocean watershed. The Bigmouth Sleeper is popular with recreational fishermen and considered to be an excellent food fish. Their long-term viability is threatened by dam construction, stream flow alteration and pollution to their water systems caused by human developments. They are also prone to expatriation by the introduction of non-native fish into their environments. There are on-going efforts to develop methods to raise them via aquaculture.