Pacific Sleeper

Pacific Sleeper, Gobiomorus maculatus

The Pacific Sleeper, Gobiomorus maculatus, whose common Spanish name is dormilón manchado, is a member of the Sleeper or Eleotridae Family, known collectively as guavinas in Mexico. Globally, there are only four species in the genus Gobiomorus, two of which are found in Mexican waters, one in the freshwater drainage systems of the Atlantic and one in the Pacific.

The Pacific Sleepers have elongated cylindrical bodies that taper at the rear. Adults are dark mottled brown and transition to white ventrally. Their fins are transparent and their pectoral fins have a dark band at the base. They are sexually dimorphic with males having longer anal fins and dorsal rays as well as rows of small dark spots on their caudal and dorsal fins. Juveniles have a dark stripe mid-body and three bars radiating from their eyes. Their anal fin has one spine and nine or ten rays and their caudal fin is rounded and has a long base. Their dorsal fins are well separated; the first has a short base with six small spines; and the second has a base shorter than the distance separating it from the caudal fin with one spine and nine rays. Their pectoral fins have 15 or 16 rays and their long widely separated pelvic fins have one spine and five rays. Their head is elongated and conical with a depression above it. Their eyes are longitudinal ovals. Their mouth is large and oblique with a projecting lower jaw equipped with small conical teeth in several rows and additional teeth on the roof of the mouth. They have large gill openings extending forward to under the mouth. They are covered with rough scales and have no lateral line.

The Pacific Sleepers are a demersal species found in freshwater rivers, creeks, and lakes with varying levels of salinity and with temperatures between 24oC (75oF) and 33oC (91oF) at elevations up to 300 feet. Juveniles are more common near the coast. They reach a maximum length of 35 cm (14 inches) with females being larger than males. They consume crustaceans and fish. Reproduction includes pelagic eggs and larvae. They are poorly studied and very little is known about their behavioral patterns.

In Mexican waters the Pacific Sleepers are found in all the freshwater systems that drain into the Pacific from Magdalena Bay southward along the southwest coast of Baja, from La Paz southward along the east coast of Baja, and from the central Sea of Cortez south along the coast of the mainland to Guatemala.

The Pacific Sleeper is most likely confused with the Spotted Sleeper, Eleotris picta (eyes very close to tip of snout), however, it is one of several freshwater Sleepers found in Mexican freshwater systems that is not well documented, poorly studied, and the source of significant confusion about this species.

The Pacific Sleepers are fairly common in Mexican freshwater of the Pacific watershed, however, they are of limited interest to most with the exception of subsistence fishermen. From a conservation perspective they are considered of Least Concern as they are widespread and common with stable populations.

Pacific Sleeper, Gobiomorus maculatus, Juvenile. Fish collected by locals with a cast net at the mouth of the San José River, Baja California Sur, August 2008, during a breach in the barrier. Length: 12.0 cm (4.7 inches). Identification courtesy of H.J. Walker, Jr. and confirmed by Dr. Phil Hastings, Scripps Institution of Oceanography, La Jolla, CA.

Pacific Sleeper, Gobiomorus maculatus, Male. Fish collected by locals with a cast net at the mouth of the San José River, Baja California Sur, August 2008, during a breach in the barrier. Length: 25 cm (10 inches). Identification courtesy of H.J. Walker, Jr. and confirmed by Dr. Phil Hastings, Scripps Institution of Oceanography, La Jolla, CA.

Pacific Sleeper, Gobiomorus maculatus, Male. Fish collected by locals with a cast net at the mouth of the San José River, Baja California Sur, August 2008, during a breach in the barrier. Length: 26 cm (10 inches). Identification courtesy of H.J. Walker, Jr. and confirmed by Dr. Phil Hastings, Scripps Institution of Oceanography, La Jolla, CA.

Pacific Sleeper, Gobiomorus maculatus, Female. Fish collected by locals with a cast net at the mouth of the San José River, Baja California Sur, August 2008, during a breach in the barrier. Length: 28.5 cm (11.2 inches). Identification courtesy of H.J. Walker, Jr. and confirmed by Dr. Phil Hastings, Scripps Institution of Oceanography, La Jolla, CA.