Does anyone know the taxonomic situation of these animals? The common name is "Southern California Steelhead" and it seems they're a Critically Endangered type of Rainbow Trout. However, when I Googled them it doesn't give me a specific subspecies, just a distinct population. Are they a population of a subspecies or an undescribed subspecies?
The steelhead trout and rainbow trout are genetically the same fish and the same species, Oncorhynchus mykiss. I know this sounds very confusing. But basically, steelhead trout are just rainbow trout that have made their way down rivers and streams to the ocean, and have gone through a process called smoltification which allows them to survive in saltwater, to live their lives in the ocean rather than freshwater. They are more silvery in color and their tail shape also changes slightly.
When it’s time for them to spawn, they return to the freshwater rivers where they were born and lay their eggs there. However, unlike other salmon species that die after they spawn, steelhead trout can spawn multiple times, returning to the ocean after each time. The crazy thing is that when the eggs hatch, they all hatch as…rainbow trout! Some of the fish from the same group of eggs may grow up to remain as rainbow trout in the freshwater while other ones may swim on to the ocean to become steelhead! Scientists don’t know exactly what it is that triggers some to remain rainbow trout and others to change to steelhead. We’re hoping to learn more about them as we have them here at the Aquarium of the Pacific.
But it gets even crazier…there are both steelhead trout AND rainbow trout living side by side in Lake Michigan (which is ALL FRESHWATER). There, the ones that exhibit the behavior of traveling upstream to spawn are the ones they call steelhead, while the rainbow trout will just lay their eggs in shallower areas of the lake but do not make the upstream trek. So how about that? Very interesting fish, huh?
There are some Distinct Population Segments of this species (like the Southern California Steelhead which are endangered) while others have healthier populations.
@ThylacineAlive I would love to know what the aquariums findings are with regards to the reason for those morphological changes. The scientific paper if one is written would be such a fascinating read!
