Burro Grunt, Rhonciscus crocro

Burro Grunt, Rhonciscus crocro, Juvenile. Fish caught within the Indian River Lagoon, Micco, Florida, May 2021. Length: 7.0 cm (2.75 inches). Catch, photograph and identification courtesy of Ben Cantrell, Sebastian, Florida.

The Burro Grunt, Rhonciscus crocro, is a member of the Grunt or Haemulidae Family, that is known in Mexico as corocoro crocro and la ticopa. 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 Burro Grunt has an oblong, strongly compressed robust body with a depth that is of 26% to 36% of standard length. They are a dark olive color dorsally that transitions to silvery ventrally. The fins are dusky. In adults the second dorsal fin has a black margin. Their flanks have dusky spotting. Their head has a small mouth with thin lips. They have 7 to 9 short, blunt, lower gill rakers. Their anal fin has 3 spines and 6 or 7 rays with the second ray being long and stout; their first dorsal fin has 13 spines; their second dorsal fin has 11 to 13 rays. They are covered with scales.

The Burro Grunt is a demersal species that is found in brackish waters over mud and sandy substrate within bays, creeks, estuaries and rivers of low to high current velocities at depths up to 15 m (50 feet). They require access to creeks and small rivers are known to ascend freshwater creeks for more than 100 miles. They reach a maximum of 33 cm (13 inches) in length and 1.85 kg (4 lbs 1 oz). They consume crustaceans and small fish. Reproduction is oviparous with distinct pairing during breeding The Burro 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 Burro Grunt is a resident of all Mexican waters of the Atlantic Ocean however their populations are poorly documented. There is a landlocked population in two freshwater lakes in Veracruz.

The Burro Grunt can be confused with the Barred Grunt, Conodon nobilis (eight prominent bars on the flanks).

From a conservation perspective the Burro Grunt is currently considered to be Data Deficient with poorly documented populations. They are caught in small quantities by artisanal fishermen utilizing beach seines and trawls and utilized as a human food. Their long-term survival has been threatened by human development in shoreline habitats and the construction of dams.