Flagfin Mojarra

Flagfin Mojarra, Eucinostomus melanopterus

The Flagfin Mojarra, Eucinostomus melanopterus, whose common Spanish name is mojarra de ley, is a species in the Mojarra or Gerreidae Family, known collectively as mojarras in Mexico. Globally, there are 11 species in the genus Eucinostomus, all found in Mexican waters, with seven in the Atlantic and four in the Pacific.

The Flagfin Mojarras have moderately deep, fusiform, and compressed bodies with a depth that is 34% to 38% of standard length. They are silvery white and the tip of their spiny dorsal fin has a wide black tip and a white band below, providing a key to identification. Their anal fins are pale yellow. Adults have no additional distinguishing marks. Juveniles have dark vertical bars on their back and sides. Their head has a concave lower profile, large eyes, and a pointed snout. Their mouth is highly extensible, pointing downward when protruded. They have smooth gill covers. Their anal fin has three slender spines, with the second spine being stronger and shorter than the third spine, and seven or eight rays. Their caudal fin is deeply forked. Their dorsal fin is elevated at the front and deeply notched; it has nine spines and ten rays. Their pectoral fins are long and reach the anal fin origin. They have nine lower gill rakers. Their lateral line is slightly arched and their head and body are covered with rough scales.

The Flagfin Mojarras are a schooling species found in shallow coastal areas over sandy and muddy bottoms, in lower coastal rivers, and in freshwater lagoons at depths up to 250 feet and in water temperatures between 24oC (75oF) and 28oC (82oF). They reach a maximum length of 30 cm (12 inches). They are diadromous and migrate up to 30 miles between freshwaters and oceanic waters on cyclical and predictable schedules but not for breeding purposes. They are found mixed with Largescale Fat Snook, Centropomus mexicanus (which they mimic) and Spotfin Mojarra, Eucinostomus argenteus. They feed during the daytime in small continuous moving schools consuming small fish, shrimp, mollusks, zooplankton, and detritus. Reproduction is oviparous and occurs at sea. They are a poorly studied species and very limited information is available about their behavioral patterns.

In Mexican waters the Flagfin Mojarras are found in all waters of the Atlantic with documented large populations within the Laguna Madre and the mouth of the Río Soto La Marina in the State of Tamaulipas and within the lagoon of the Isla de Sacrificios in the State of Veracruz.

The Flagfin Mojarra is most likely confused with the Silver Jenny, Eucinostomus gula and the Spotfin Mojarra, Eucinostomus argenteus, but both lack the black-tipped dorsal fin. It is also very similar to the Pacific Flagfin Mojarra, Eucinostomus currani, which is a resident of the Pacific Ocean.

The Flagfin Mojarras are too small to be of interest to most. In some areas they are caught with cast nets, beach seines, set nets, handlines, and bottom trawls where they are marketed fresh (but in low demand) or used as live bait. From a conservation perspective they are considered of Least Concern with stable and widely distributed populations.

Flagfin Mojarra, Eucinostomus melanopterus. Fish caught off the Juno Beach Pier, West Palm Beach, Florida, February 2017. Length: 15.0 cm (5.9 inches). Catch and photo courtesy of George Brinkman, Guelph, Ontario, Canada.