Photo Credit: Elea Medina
The opah (Lampris guttatus) is a large, mid-water pelagic fish that occurs seasonally in the Southern California Bight (SCB). While they are not targeted, they are taken incidentally in both local recreational fisheries for tuna and the California drift gillnet fishery targeting swordfish. In recent years there appears to have been an upsurge in opah catch and the rich meat has become increasingly popular in seafood markets. Despite their value to commercial and recreational fishermen, little research on the basic biology and ecology of opah has been conducted, especially in the SCB. For example, there are few data on foraging ecology, size composition in fisheries, essential habitat and stock structure. To begin to fill some of the data gaps, the Southwest Fisheries Science Center began collecting biological samples from opah in 2009 and initiated an electronic tagging program in 2011.
Analyses of the biological samples and the data provided by the tagging program have revealed a plethora of information. Genetic analysis has determined that there are multiple different species of opah, those caught off California being a different species than those caught off Hawaii. Opah also appear to have a unique gill arch structure which has never been seen before. The unique structure might help scientists understand their ability to forage deep in the water column, from generally 50 m at night down to 200 m during the day. The vertical movements are likely due to opah following prey with similar migrations. Opah primarily forage on squid and deep water fishes such as barracudinas, a small elongated fish of up to 50 cm. Barracudinas are notable mid-water predators and they are an important food for large fishes such as tunas, swordfish, bigeye thresher shark and, evidently, opah.
SWFSC scientists plan to continue the biological sampling and genetic analysis of opah to further explore intraspecific differences. This will include stomach processing to identify the important prey for opah and whether the diet changes with environmental conditions, and more dissections of the gills and whole fish to learn about the anatomy of opah and their swimming mechanics. Scientists also hope to continue tagging opah to learn about their movements and range. This research will provide the basic life history information necessary for future population assessments and management. Historical catch data may also show correlations between opah catch and abundance with changes in sea surface conditions such as El Niño and La Niña.
Link to FishWatch page on opah
Link to Union Tribune article on opah
Link to Runcie et al. article on opah cranial endothermy
For more images of opah and a brief summary, visit our Opah Image Gallery
Further information on the Fisheries Resources Division’s Large Pelagics program can be found on the About Large Pelagics Program page