Sand Grunt, Rhonciscus branickii
Sand Grunt, Rhonciscus branickii, Juvenile. Fish caught with a cast net from coastal waters off Puerto Adolfo Lopez Mateos, Baja California Sur, August 2017. Length: 10.0 cm (3.9 inches). Identification courtesy of H.J. Walker, Jr., Scripps Institution of Oceanography, La Jolla, California.
Sand Grunt, Rhonciscus branickii, Juvenile. Fish caught off the dock in Mazatlán, Sinaloa, October 2018. Length: 11.4 cm (4.5 inches). Photograph courtesy of George Brinkman, Guelph, Ontario, Canada.
Sand Grunt, Rhonciscus branickii. Fish caught from coastal waters off Point Palmilla, Baja California Sur, February 2018. Length: 22 cm (8.7 inches).
Sand Grunt, Rhonciscus branickii. Fish caught from coastal waters with Magdalena Bay, Baja California Sur, July 2016. Length: 26 cm (10 inches).
Sand Grunt, Rhonciscus branickii. Fish caught from coastal waters off Point Palmilla, Baja California Sur, February 2014. Length: 28 cm (11 inches).
The Sand Grunt, Rhonciscus branickii, is a member of the Grunt or Haemulidae Family, that is also known as Branick’s Grunt and in Mexico as roncacho arenero and roncador. Globally, there are three species in the genus Rhonciscus, and all three are found in Mexican waters, one in the Atlantic and two in the Pacific Ocean.
The Sand Grunt has a relatively slender elongated compressed body with a depth that is 32% to 34% of standard length. They have an overall uniform silvery appearance with brown tinges, a yellow-brown gill cover, and no additional significant markings. They have a large head, large eyes with yellow irises, and thick lips. Their anal fin has 3 spines, the second of which is long and stout, and 7 rays; their dorsal fin has 13 spines, a key to identification, and 11 or 12 rays; and, their pectoral fins are long. This species is particularly well-protected with a long stout second anal spine, the length of which is two times the diameter of their eyes and four times the size and length of their first anal spine, and an enormous first pelvic spine that is approximately two-thirds the length of their second pelvic ray. They are covered with scales and have a strong lateral line.
The Sand Grunt is an inshore demersal species that is found over sandy substrate and at depths up to 91 m (300 feet), as established by a fish that I caught. They will also enter muddy bays and estuaries. They reach a maximum of 31 cm (12 inches) in length and are under 1.0 kg (2 lbs 3 oz) in weight. The Sand Grunt 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 Sand Grunt is a resident of Mexican waters of the Pacific Ocean but has a very limited distribution being found from Magdalena Bay, Baja California Sur, southward along the southwest coast of Baja, from Loreto, Baja California Sur, southward along the southeast coast of Baja (these southerly limit being established by fish that I caught), and along the coast of the mainland from Mazatlán, Sinaloa, south to Guatemala.
The Sand Grunt can be confused with the Panamic Grunt, Rhencus panamensis (dark blotch at top of gill cover; slender second anal spine), the Longspine Grunt, Rhencus macracanthus (12 dorsal spines; dark spot on top of gill cover and pectoral fin base), and the Yellowstripe Grunt, Haemulopsis axillaris (black blotch on top border of the gill cover; dark lines on flank; third anal spine longer than second).
From a conservation perspective the Sand Grunt is currently considered to be of Least Concern with stable, widely distributed populations. They are small in stature and of limited interest to most. They are viewed as marginal table fare by locals.