Counting scales and caudal peduncle proportion (black redhorse example)

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Jknuth
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Counting scales and caudal peduncle proportion (black redhorse example)

I wanted to share some tips on how to count lateral line scales and the scales around the caudal peduncle as well as caudal peduncle proportions. 
I am just wrapping up a Black redhorse illustration and figured this would be a good example since these measurements are ket to properly id'ing this species.

 

Caudal Peduncle 
The caudal peduncle is the tail section of the fish. It starts and the posterior end of the base of the anal fin and continues to the posterior edge of the hypural plate.

 

Hypural Plate
The Hypural plate is the last bone in a fishes vertabre. It is not typically visible under the skin on most species. Although some species have a small noticable dent or divet at this point.  It can however be felt under the skin. Its where the muscle tissue stops on the tail and the tail fin begins. But be aware that the tail actaully starts beneath the skin and there are normally scales that continue onty the fin. If you hold a fish and pinch the base of its tail lightly and move the tail from side to side you can feel the "knuckle" as som call it.  This is the edge of the hypural plate. 

 

 

Cleithrum
The Cleithrum is the collar bone found behind the gills on the body of the fish. 

 

 

Lateral line scale count
When counting scales on a lateral line you start at the first fully formed poored scale behind the cleithrum.  
The scale count continues to the last scale on the hypural plate. Its important to not count the scales past this point. Often they can continue past this and well onto the fin.  This will give you a false scale count in the lateral line leading to issues with identification. 
The fish below has a lateral scale count of 47. Black redhorse typically have a scale count of 45 or more and golden redhorse a scale count of 44 or less. 

 

 

Caudal peduncle scale count
When counting the scales around the caudal peduncle this is the method I was taught to use in the field. Often it can be tricky to get this count if the fish is still alive and moving. So rather than count all the way around I count one side while its laying flat. Find a good center point on the peduncle. I count the scales on the side of the peduncle folloing the arc of scale. I disregard the ventral scale and the dorsal scale. 
For example on the fish pictures there are 5 scales on the side, 1 dorsal, and 1 ventral. There are 5 scales on the oppisite side. 5+5+1+1 = 12 scales around the caudal peduncle. 

 

 

Caudal peduncle proportions
Measuring the proportions of the caudal peduncle can be tricky in the feild. a calipers is helpful but often I find doing this at home with a good photo of the fish laying flat is far easier. 
First the caudal peduncle length. From the posterior edge of the base of the anal fin to the posterior edge of the hypural plate. Then the depth or height of the caudal peduncle at its center. 
These measurements are taken and then compared. 
In the case of the fish below it is 1:0.59 The caudle peduncle depth is 59% of its length. 
Black redhorse typically have depth that is 59.9% or less and Golden redhorse have a depth of 62% or more. 

 


 

Outdoors4life
Outdoors4life's picture
Josh you rock!

Josh this is great. 
I am so glad you got this posted. We will have to see if there could be an ID section with certain species such as Golden/Black Redhorse that get mixed up often. 

Typically after seeing enough, we can ID by just looking but it is great to be able to prove the point by knowing how to count the lateral line or Caudal peduncle scale count.

This is the kind of info with graphics that really make the site unique. 

It is all perspective!

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Eric Kol
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This is pure gold

This is pure gold

Carpy Diem!

FP4LifesDad
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Awesome buddy, very cool how

Awesome buddy, very cool how you explained it and the pictures kick butt, thanks for making it simple!

andy
andy's picture
What a great explanation!

Thanks so much for putting this together, JKnuth.  We should really build out an article that contains this information.  Invaluable!

okcaveman
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Very good! Thanks!

Very good! Thanks!