Opah Biology

Opah species distributionDNA barcoding

Very little is known about the life history of the opah (Lampris guttatus), and the only other extant recognized species in the genus is Lampris immaculatus. Observations from researchers throughout the years suggested the presence of two distinct morphotypes of Lampris guttatus in the North Pacific. SWFSC scientists collaborated with researchers from the Pacific Islands Fisheries Science Center (PIFSC) to sequence genes for these two morphotypes and other specimens collected worldwide to better clarify the taxonomy of this group of fishes. The results of their genetic sequencing produced five strongly diverged and well-supported clades, likely representing separate species. They concluded that opah are likely a complex of at least five separate species, which would have implications for their management. 

Read more about the genetic research here: Hyde, J. R., Underkoffler, K. E. and Sundberg, M. A. (2014). DNA barcoding provides support for a cryptic species complex within the globally distributed and fishery important opah (Lampris guttatus). Molecular Ecology Resources, 14: 1239–1247.

A. Distribution of elevated temperature in the opah.
B. Internal body temperature of an opah in comparison to water temperature while swimming at depths of 60-100 meters. Whole-body endothermy 

SWFSC researchers have recently reported in ScienceThe previous link is a link to Non-Federal government web site. Click to review NOAA Fisheries Disclaimer that the opah is the first fish known to have a whole-body form of endothermy. Unlike tunas and lamnid sharks which are capable of warming specific regions of the body (regional endothermy), the opah is the only vertebrate outside of mammals and birds known to circulate warmed blood throughout the body. The bulk of its heat appears to be generated by its unusually large pectoral muscles which are used in continuous swimming. These muscles are insulated from water by a thick layer of fatty connective tissue. In addition, the opah has a unique series of extensive counter-current heat exchanges inside its gill arches which are used to minimize heat loss at the gills where blood comes in close contact with the water to absorb oxygen and release carbon dioxide during respiration. Thus the entire body core including the swimming musculature, visceral organs, and the heart are warmer than the environment. Although warm blood perfuses the entire body, the cranial region (eye and brain) is warmer than the body core. Previous work by SWFSC biologists in collaboration with researchers from California State University Fullerton (CSUF), University of Hawaii (UH), and University of California San Diego (UCSD) found that the proximal region of the paired lateral rectus extraocular muscles (used in controlling eye movement) appears to generate additional heat, which is locally conserved by small counter current heat exchangers. The ability of opah to warm its entire body allows for enhanced physiological function (e.g., increased swimming speeds, faster reaction rates) in its relatively deep and cold environment, providing a distinct advantage over its slower, cold-bodied prey. In addition, unlike many other predators, opah do not need to return to surface waters to warm between feeding bouts, allowing them to remain at depth foraging.

Read more about the research here:

Wegner, N. C., Snodgrass, O. E., Dewar, H., and J. R. Hyde. (2015). Whole-body endothermy in a mesopelagic fish, the opah, Lampris guttatus. Science, 348 (6236): 786-789.

Runcie, R. M., Dewar, H., Hawn, D. R., Frank, L. R., and Dickson, K. A. (2009). Evidence for cranial endothermy in the opah (Lampris guttatus). The Journal of Experimental Biology, 212(4): 461–470. 

Opah Sexual Dimorphism

Sexual Dimorphism

Sexual dimorphism is the presence of different physical traits (coloring, shape, size) between male and female members of the same species. In opah, differences in the pectoral girdle of sexually mature fish make the sexes easily distinguishable. In males, the girdle is thick and concave and is shaped with a much deeper, abrupt angle than the female girdle. The female girdle is narrow and convex and more gradual in the angle in which it rounds. 

Read more about the research behind opah morphology.The previous link is a link to Non-Federal government web site. Click to review NOAA Fisheries Disclaimer.