Opaleye, Girella nigricans
The Opaleye, Girella nigricans, whose common Spanish name is chopa verde, is a species in the family Kyphosidae, the Sea Chubs, known as chopas in Mexico. Globally, there are eighteen species in the genus Girella, of which two are found in Mexican waters, both in the Pacific.
The Opaleyes have elongated oval compressed bodies that have a depth that is 38 – 42% of standard length. They are olive-green to gray-green with two pale spots on their upper back below the mid-dorsal fin that are absent in mature adults. Most have a white bar across their snout between the eyes. They have bright blue-green eyes for which they are named. Their coloring transitions to a uniform dark brown upon death. They have a short blunt head and a small mouth with thick lips opening at the front. They have small incisiform teeth set horizontally in the mouth with flattened three-pointed tips and a curved hockey-stick shape. Their anal fin has three spines and ten to thirteen rays, their caudal fin is concave, their dorsal fin is continuous with twelve to fourteen spines folding down into a scaly grove and twelve to fifteen rays, and their pectoral and pelvic fins are relatively short. With the exception of the caudal fin, all their fins are blunt to rounded. Their body is covered with small, thick, and rough scales.
The Opaleyes are found in large schools, normally demersal, within rocky areas with an abundance of algae growth at depths up to 105 feet; they will occasionally enter estuaries. Juveniles are pelagic and found near the surface often within floating debris. They reach a maximum length of 66 cm (26 inches). They are an eurythermal species being able to tolerate water temperatures as low as 46oF and as high as 95oF. They are diurnal omnivores grazing on algae and preying on invertebrates. They are found along the entire west coast of Baja, with isolated populations found throughout the Sea of Cortez, and are absent south of Mazatlán along the west coast of the mainland.
The Opaleye is most likely confused with the California Halfmoon, Medialuna californiensis (black blotch at top of gill cover), the Gulf Opaleye, Girella simplicidens (pointed anal and dorsal fins; three to four white spots; bright blue eyes), and the Zebraperch, Hermosilla azurea (eight faint bars on sides; black spot at pectoral fin base).
The Opaleyes are considered marginal table fare and only retained by subsistence fishermen.