Trout Fins

A trout’s fins are its means of locomotion, affording it near total control inside the 3D world of water.

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I was hanging over the bridge rail at Big Springs, participating in that quintessential Island Park activity of watching the huge trout below as they lazily finned in the crystal-clear waters.

I observed how the fins worked independently and jointly to keep the fish in an exact spot and in an upright position. I doubt that the fish had to consciously consider the actions of their fins any more than I have to concentrate on the position of my toes and feet when I walk. It just seemed automatic. Curious, I looked into the function of trout fins when I got home.

Trout have eight fins. First is the tail or caudal fin. Then there is the dorsal (back) fin, two pelvic fins and a single anal fin in back and two pectoral fins in front, located on the bottom side of the fish. Lastly, there is a small fin between the dorsal and tail fins called an adipose fin. This small fin has no bone and is made up of fatty tissue.

A watery environment is much more like life in the air than the experience we have walking on land with gravity to keep us oriented. Water dwellers have to concern themselves with up and down—pitch, left and right—yaw, and roll, just as an airplane would. They use fins to control these variables to keep their bodies properly oriented in this 3D world.

Pelvic fins control pitch—whether or not the head points up, down or straight ahead. Dorsal and anal fins control roll, much as a skeg keeps a sailboat from rolling over.

The pectoral fins are the workhorses of all fins. They help control yaw and pitch and serve as the rudder for direction. They are also the primary fins used for braking and can operate independently of other fins and each other.

The caudal or tail fin is the strongest fin. It is mainly used for thrust and can propel a stationary one-pound trout to 22 mph in one second.

What about the adipose fin? Is it simply a vestigial fin from some era long ago in a trout’s evolutionary development as scientists have thought? It has been considered sacrificial and removing it has been used as a way to mark large groups of fish. However, recent research demonstrated that when it is removed on juvenile rainbow trout, they experienced a reduced swimming efficiency compared to fish with unclipped fins. In short, the adipose fin helps to reduce drag by maintaining the boundary layer, that thin layer of water molecules next to the skin, intact longer.

Trout are often found in very fast-moving water. Common sense might suggest that these trout are spending a lot of energy to maintain their position, but the opposite is true. Like a hawk taking advantage of wind to remain in position without beating its wings, trout can find the “sweet spots” in a fast-moving water column where they expend less energy maintaining station than in slower moving water. Judicious finning keeps them in the perfect position.

Hatchery trout raised to catchable size often show the result of life in a raceway with pectoral and pelvic fins worn down to nubs. These fish would likely not fare well if released into swift waters. They don’t have the control they need to negotiate the currents.

We humans think we are all big and bad with our opposable thumbs. However, if we lived in the water, we might wish they were fins instead.

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Help Idaho Wildlife

When we traveled across the state in October 2017, most of the vehicles we saw using the wildlife management areas did not have wildlife plates. Buying wildlife plates is a great way for non-hunters and hunters alike to support wildlife-based recreation like birding.

C'mon folks, let's help Idaho's wildlife by proudly buying and displaying a wildlife license plate on each of our vehicles! 

See below for information on Idaho plates. Most states have wildlife plates so if you live outside Idaho, check with your state's wildlife department or vehicle licensing division for availability of state wildlife plates where you live. 

And tell them that you heard about it from Nature-track.com!

Wildlife License Plates

Great news! as of 2024, there are three NEW designs for license plates. They still are bluebird, cutthroat trout and elk, but they are beautiful.

Idaho Wildlife license plates provide essential funding that benefits the great diversity of native plants and wildlife that are not hunted, fished or trapped—over 10,000 species or 98% of Idaho’s species diversity. Game species that share the same habitats (such as elk, deer, antelope, sage-grouse, salmon, trout) also benefit from these specialty plates.

No state tax dollars are provided for wildlife diversity, conservation education and recreation programs. Neither are any revenues from the sale of hunting or fishing licenses spent on nongame species. Instead, these species depend on direct donations, federal grants, fundraising initiatives—and the Idaho Wildlife license plates.

Both my vehicles have Bluebird Plates. I prefer the bluebird because the nongame program gets 70 percent of the money from bluebird plates, but only 60 percent of the money from elk and trout plates - 10 percent of the money from elk plates supports wildlife disease monitoring and testing programs (to benefit the livestock industry) and 10 percent from cutthroat plates supports non-motorized boat access.

Incidentally, in 2014, the Idaho Legislature denied the Department of Fish and Game the ability to add new plates or even to change the name of the elk and cutthroat plates (very specific) to wildlife and fish plates, a move that would have allowed for changing images occasionally and generating more revenue. It would seem that they believe that we Idahoans don't want a well funded wildlife program.

I think it is time we let the Legislature know that Idahoan support wildlife funding and that we would like to see these generic plates come to fruition.