Long-armed River Prawn, Macrobrachium tenellum

Long-armed River Prawn, Macrobrachium tenellum. Collected out of the San José del Cabo Rio, Baja California Sur, with a cast net, August 2011. Length: 7.0 cm (2.8 inches).

The Long-armed River Prawn, Macrobrachium tellellum (Smith, 1871), is a member of the Palaemonidae Family of Palaemonid Shrimp that is also known as the Long-clawed River Prawn and in Mexico as chacal’n, langostino, manocarrizo and manopalito.

The Long-armed River Prawn Long-armed River Prawn has a right claw arm that is about 1.5 times longer than the left claw arm and it is almost always closed and the left one is usually open. The body is yellowish brown, becoming dusky dorsally. They reach a maximum length of  9.0 cm (3.5 inches).

The Long-armed River Prawn is found in fresh water rivers and estuaries in both flowing water or in stagnant pools at depths up to 3 m (10 feet). This species is amphidromous living in fresh water, but returning to brackish water to spawn. They are omnivorous scavengers, feeding on algae, detritus and small invertebrates. They have long been used as a food source by the local indigenous people for centuries and sold on a limited basis commercially. They are currently considered a very good aquaculture specimen as they are not aggressive, and have a good tolerance for waters with varying amounts of salinity, temperature changes, and oxygen levels.

The Long-armed River Prawn is a resident of the Pacific and found along the west coast of the Baja Peninsula, from the Santa Rita drainage, near the village of Marecuaco, Baja California Sur, south to Cabo San Lucas and on the east coast of the Baja from from Mulegé to the Los Cabos area, Baja California Sur.  They are also found along the coast of the mainland from Guaymas, Sinora southward to Guatemala.

Synonyms include Palemon longipes and Palemon tenellus.