Sockeye salmon (scientific name: Oncorhynchus nerka) have orange colored meat because of the krill they eat while in the ocean. The sockeye is one of the smallest, but most prized of the Pacific salmon. They hatch in freshwater, where they remain for up to three years. They then travel to the ocean, spending 1-4 years at sea before returning home to spawn and die. sockeye die within 1-2 weeks after spawning. Read more about Sockeye at National Geographic.
Pacific salmon (Oncorhynchus spp.) are famous for their homing migrations from oceanic feeding grounds to their natal river to spawn. During these migrations, salmon travel through diverse habitats (e.g. oceans, lakes, rivers), each offering distinct orientation clues and, perhaps, requiring distinct sensory capabilities for navigation. Prior to their seaward migration, juvenile salmon learn (imprint on) odors associated with their natal site and later, as adults, use these odor memories for homing. Our understanding of this imprinting process is derived primarily from studies using artificial odorants and hatchery-reared salmon. Recent findings suggest, however, that such studies may underestimate the complexity of the imprinting process in nature. Summary from HOMING IN PACIFIC SALMON: MECHANISMS AND ECOLOGICAL BASIS by ANDREW H. DITTMAN AND THOMAS P. QUINN. Read the full article.
Juvenile Chinook may spend from 3 months to 2 years in freshwater before migrating to estuarine areas as smolts and then into the ocean to feed and mature. Chinook salmon remain at sea for 1 to 6 years (more commonly 2 to 4 years), with the exception of a small proportion of yearling males (called jack salmon) which mature in freshwater or return after 2 or 3 months in salt water. Read more from NOAA Fisheries Office of Protected Resources.
An assemblage of fossil sockeye salmon was discovered in Pleistocene lake sediments along the South Fork Skokomish River, Olympic
Peninsula, Washington. The fossils were abundant near the head of a former glacial lake at 115 m elevation. Large adult salmon are concentrated
in a sequence of death assemblages that include individuals with enlarged breeding teeth and worn caudal fins indicating migration, nest digging,
and spawning prior to death. The specimens were 4 yr old and 45–70 cm in total length, similar in size to modern sockeye salmon, not landlocked
kokanee. The fossils possess most of the characteristics of sockeye salmon, Oncorhynchus nerka, but with several minor traits suggestive of pink
salmon, O. gorbuscha. This suggests the degree of divergence of these species at about 1 million yr ago, when geological evidence indicates the
salmon were deposited at the head of a proglacial lake impounded by the Salmon Springs advance of the Puget lobe ice sheet. Surficial geology
and topography record a complicated history of glacial damming and river diversion that implies incision of the modern gorge of the South Fork
Skokomish River after deposition of the fossil-bearing sediments. Summary from “Spawning sockeye salmon fossils in Pleistocene lake beds of Skokomish Valley, Washington” by Gerald R. Smith, David R. Montgomery, N. Phil Peterson, and Bruce Crowley. Read the full article here.
Salmon know when their most common predator is around, because they can tell that it’s eaten salmon before, new research shows. Young fish can do this too, even if they’ve never encountered that particular predator before. Read the full article here.
The adipose fin, commonly clipped on hatchery Salmon, has always been thought to be without a purpose. New science suggests differently.
A wide variety of rudimentary and apparently non-functional traits have persisted over extended evolutionary time. Recent evidence has shown that some of these traits may be maintained as a result of developmental constraints or neutral energetic cost, but for others their true function was not recognized. The adipose fin is small, fleshy, non-rayed and located between the dorsal and caudal fins on eight orders of basal teleosts and has traditionally been regarded as vestigial without clear function. We describe here the ultrastructure of the adipose fin and for the first time, to our knowledge, present evidence of extensive nervous tissue, as well as an unusual subdermal complex of interconnected astrocyte-like cells equipped with primary cilia. The fin contains neither adipose tissue nor fin rays. Many fusiform actinotrichia, comprising dense striated macrofibrils, support the free edge and connect with collagen cables that link the two sides. These results are consistent with a recent hypothesis that the adipose fin may act as a precaudal flow sensor, where its removal can be detrimental to swimming efficiency in turbulent water. Our findings provide insight to the broader themes of function versus constraints in evolutionary biology and may have significance for fisheries science, as the adipose fin is routinely removed from millions of salmonids each year. Summary from “Neural network detected in a presumed vestigial trait: ultrastructure of the salmonid adipose fin,” written by J. A. Buckland-Nicks, M. Gillis and T. E. Reimchen.