Opaleye, Girella nigricans
The Opaleye, Girella nigricans, whose common Spanish name is “Chopa Verde”, is a member of the Sea Chub or Kyphosidae Family, known collectively as “Chopas” in Mexico.
The Opaleye has an elongated oval compressed body with a width that is 38 to 42% of standard length. They are an olive green to gray green with two pale spots on the upper back below mid-dorsal fin that are absent in mature adults. Most have a white bar across the snout between the eyes. They have bright blue-green eyes for which they are named. The colors transition to a uniform dark brown upon death. They have a short blunt head with a small mouth that has thick lips that opens at the front with small incisiform teeth set horizontally in the mouth with flattened three-pointed tips and a curved, hockey-stick shape. They have an anal fin with three spines and ten to thirteen rays the front, a concave caudal fin, a continuous dorsal fin with twelve to fourteen spines, that fold down into a scaly grove, and twelve to fifteen rays, and pectoral and pelvic fins that are relatively short. Except for the caudal fin the fins are blunt to rounded. The body is covered with small, thick, rough scales.
The Opaleye reach a maximum length of 66 cm (26 inches). They are found in large schools, normally demersal, to depths of 105 feet within rocky areas with an abundance of algae growth; they will occasionally enter estuaries. The juveniles are pelagic and found near the surface often within floating debris. The species is an eurythermal species being able to tolerate water temperatures as low as 46o and as high as 95oF. They are diurnal omnivores grazing on algae and preying on invertebrates. They are found from along the entire west coast of Baja and with isolated populations found throughout the Sea of Cortez; they 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 with bright blue eyes), and the Zebra Perch, Hermosilla azurea (eight faint bars on its sides and a black spot at the pectoral fin base). This is species is considered to be marginal table fair and only retained by subsistence fishermen.