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OCH BLOG

Species Spotlight: Opaleye

Updated: May 6, 2023

When visitors stroll down by the tidepools, they will often see a tiny brown fish (with one or two white dots on its back) snacking on algae growing around the tidepools. If visitors crouch close for a better look, these tiny fish will quickly dart into the closest crevice or rock to hide. These tiny fish are baby opaleyes, and the tidepool habitat serves as their temporary nursery. The opaleye lifecycle highlights the importance of a healthy tidepool and its contribution to different parts of the ocean, such as the kelp forest.


Adult Opaleye fish. Photo credit: Peter J. Bryant (University of California Irvine)

Opaleyes (Girella nigricans) or rudderfish are a non-migratory, rayed-finned species. Their geographic range is across the eastern Pacific ocean from San Francisco Bay to Baja California (fishbase). When opaleyes reach maturity in 2 to 3 years, they have the following key characteristics: colors ranging from gray-green to brown, laterally compressed oval-shaped bodies, and a body length up to 26 inches (georgiaaquarium; wikipedia). Though the white dots are a distinct trait, they can fade when the fish reaches adulthood (SiMON). As for their habitat, they inhabit shallow waters and intertidal zones across the eastern Pacific. By extension, key areas include rocky areas, tide pools, and kelp beds (georgiaaquarium). However, where they are found may depend on what stage of their life cycle they are in.


Adults are typically found further in the ocean’s kelp beds or rocky shores. They will be found as far down as 30 meters, and they can withstand temperatures from around 46 to 95℉ (guidesly). When April, May, and June approach, the adults will form schools around these areas and broadcast spawn (wildlife.ca.gov), a reproduction method where the adults release gametes (sperm & egg) out into the ocean. As a result, fertilization occurs by chance in the ocean, and the parents do not raise their offspring (fishbase.se). Though this process can occur miles offshore, the juveniles will form schools of about 24 individuals and eventually seek refuge in tidepools (wildlife.ca.gov).


In contrast to the adults, the juveniles are typically around a few inches (or less) long. Being such a tiny fish in the ocean means being surrounded by various threats, such as larger predatory fish, harsh currents and storms, etc. This is where the tidepools play a role in the opaleye lifecycle. The tidepools not only act as a temporary nursery, but they provide an enclosed space to grow and dart away from potential threats.


Juvenile Opaleye fish. Photo credit: Evie Andrade

Opaleye juveniles are well adapted to the tidepool habitat and will usually stay in them for 2 years (ocregister), sustained by the algae growing in the pool's rocky surface (wildlife.ca.gov). Though larger spaces and flourishing tidepools are preferable, they are capable of surviving in harsh conditions. Opaleyes can temporarily breathe out of the water and survive in shallow pools further from the ocean (guidesly). As they grow bigger, they will seek deeper waters in the ocean and soon, the whole life cycle will start again.


Whether they are small juveniles in the tidepools or fully-grown adults swimming through the kelp forest, these fish play two important roles in both ecosystems: grazing algae and sustaining the ocean food web. By being a grazer, opaleyes help prevent algae takeover in both the tidepools and kelp forest. Their grazing provides an opportunity for immobile organisms to flourish and compete with algae (ucsb.edu). As for the other role, opaleyes feed various species, even those found outside the tidepool environment. These can include more open ocean species, such as seals, seal lions, and larger fish, and even inland birds, such as eagles and egrets (SIMoN).


Opaleye in Kelp Forest. Photo credit: SIMoN

The opaleye population is fairly stable and they are designated LC (least concern) by the IUCN. However, improper tidepool etiquette can harm these fish. Visitors can scare off the fish by trampling or swimming in tidepools. Additionally, attempts to collect the fish with pails and nets can threaten local populations.


Luckily there are resources to safely navigate and learn about the tidepools. According to the California Department of Fish & Wildlife, all Marine Protected Area (MPA) tidepools across Southern California follow the same protocol: tidepools must be left alone, and picking any animals up is not allowed (lagunaoceanfoundation.org). If you are interested in learning more about tidepool safety and wildlife in Orange County, the Laguna Ocean Foundation and OC Habitats offer in-person educational tours for an immersive experience.


By respecting the tide pools and its creatures, visitors can do their part to ensure the opaleye successfully goes through its lifecycle and contributes to the ocean’s ecosystems.


Want to read more? See our guide through the tidepools here!


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