Opaleye

The body of Girella nigricans is laterally compressed and oval in shape. The snout is blunt and short, with a thick-lipped small mouth located at the front. The species is dentally polymorphic, with some juveniles transitioning from tricuspid teeth to simple teeth. The fins are all relatively short and rounded to blunt in shape. The dorsal fin is continuous and the tail fin has a straight margin. The dorsal fin of opaleye consists of soft rays and spines, in which the dorsal soft rays are longer or about equal to the dorsal spines. The dorsal fin has 12 to 14 spines (anterior) and 12 to 15 soft rays (posterior). The anal fin has three spines and 10 to 13 soft rays. The paired fins, which are the pectoral and pelvic fins, are relatively short. Adults are grey-green to olive green in color in life, with two to six lighter colored spots on the middle of the upper back.

Opaleye are endemic to the Eastern Pacific Ocean, and their geographic range spans from San Francisco, California to Baja California, Mexico. They are most abundant south of Point Conception. Opaleye spend their adult lives in kelp beds of the rocky subtidal zone, while juveniles inhabit the intertidal zone, often in tidepools.

Opaleye are omnivorous fish, however the majority of their diet is herbivorous. Primarily, they feed on red and green algae and seagrasses. They do feed on kelp as well, but less often than other types of algae. Small organisms that live on the algae they eat are also incorporated into their diet. Although the proportion of their diet that consists of animals is very small, they do sometimes feed on crustaceans, hydroids, and other small animals. Their feeding habits depend on factors such as habitat, water temperature, and digestive system morphology. In warmer water temperatures, opaleye tend to be more herbivorous, feeding on a higher amount of algae than they do in colder water. Also, opaleye that are more herbivorous usually have longer guts allowing them to digest plant material more easily.

Opaleye exhibit homing behavior, meaning that they continuously return to a specific tidepool or area. Homing behavior is predominantly seen in juvenile opaleye, as they spend the first part of their lives living in tidepools where they can leave and return to one specific pool. This behavior decreases as the fish grow older, because they eventually leave the intertidal area for the subtidal zone.

Some juvenile opaleye individuals have shown cleaning behavior, where they remove scales or ectoparasites from other fish species. However, this behavior is not done habitually.

Pre-juvenile opaleye have been known to sometimes aggregate under floating objects like masses of kelp and jellyfish, both offshore (before reaching the intertidal zone) and in tidepools.

Opaleye are pelagic spawners, where the eggs and larvae are released into open water and are free floating. This spawning occurs in April, May, and June. As juveniles, they migrate closer to the shore in small schools of around two dozen or less, usually moving into tidepools. For most young opaleye this happens around late June when the fish are about two months old, and around one inch long. They stay in the intertidal zone for anywhere between one year to two or more years. Living in tidepools allows the juveniles to grow and develop without the presence of large predators that do not inhabit this area. Eventually, they make their way back to deeper waters, where they mature and spawn, usually around age two or three. They typically spawn in kelp beds.

On the IUCN Red List, opaleye are listed as least concern. Their populations are stable with no indication of population decline. There are no major threats to opaleye populations. The geographic range of opaleye does include multiple Marine Protected Areas, although the species itself does not have any conservation measures. There is a rare population in the Gulf of California for which there is concern. In fisheries, opaleye are caught mainly for recreational purposes, however they are caught incidentally in commercial fisheries as well. They are sometimes sold in live fish markets. Mainly they are caught using hook and line, and sometimes by spear. Because they are typically incidental catch and are abundant, fisheries do not have a negative impact on their populations.