You might not know that Southern California is host to a struggling population of Oncorhynchus mykiss, or Steelhead Trout. You may know these fish better by other names, Rainbow trout, for example. You may know them by the way they appear when pan fried. The ones you are eating, are maybe farm raised or caught in other parts of the world where they are more abundant than in Southern California.
These fish have many different names because of the many different forms they can take in their lifetimes. Like all salmonids they swim up river to spawn. However unlike the other species, they do not always die right after spawning and can spawn multiple times. In fact, they do not always swim up the river to spawn, as some can live in the river all year round and never venture to the ocean. These river dwellers, or residents, are rainbow trout. The fish that make the journey to the ocean are the steelhead. The rainbow trout are named thus due to their beautiful spotted coloration, filled with purples and flecks of gold. The steelhead get their name from the silvery steel coloration they gain when living life in the ocean.
Now you may be asking how can these fish have two completely different lifestyles but be the same species? Well let us break it down. Two adults mate, and the female digs a hole in the streambed using her tail and body. She flops around in the gravel, its not the most majestic act. After excavating the hole, she lays eggs that the male next to her fertilizes. These eggs are then buried in a specific section of the hole with consistent water flowing over that brings oxygen to the eggs.
The little fish emerge after a few weeks with their yolk sacs still attached. These are called alvins and swim around in their nest for a few more weeks. Soon these grow into fry, and consume their egg sacs entirely. Now they feed on small insects for the most part.
Soon the time comes to decide their future, stay in the stream, or venture to the ocean? We are talking about Southern California, and although this area is well endowed, it is missing one thing in particular. RAIN.
Many creeks cannot flow out to the ocean without rainfall, and many of the creeks in Southern California have this exact issue. So the young fish living in these creeks physically cannot head out to the ocean, and are forced to be rainbow trout. However, there are some systems with good flow even in the dry years, and these young fish can head out to sea. On their journey downstream they will smolt, and gain interior and exterior features that allow them to survive in the salt water.
Even stranger still, some will reach the lagoon, or estuary at the bottom of the river. This habitat is mixed with some salt water from the sea and some freshwater from the river. Here some of the fish stay, these are lagoon-anadromous. Then around February, the breeding season begins and the fish, steelhead, rainbow, or lagoon-anadromous, all begin making nests in the riverbed. All three types can breed with one another, which is how the population can overcome the many obstacles in its way.
Depending on the stream they are born in Oncorhynchus mykiss can have three different ways of living. Particularly in Southern California, droughts are frequent and conditions are harsh. So the ability of these fish to adapt to the varying conditions has seen them survive to this day. Although their population was once near 50,000 and today a mere 500 individuals inhabit the region.
Please keep your waterways clean, and see what you can do to lower your carbon footprint, as the rising temperatures make the droughts more and more severe. If we can lend a helping hand to these fish, and in the long run back to ourselves, we may see a future for both humans and Oncorhynchus mykiss.