What physical feature is considered the most reliable constant differentiator between Channel Catfish and Blue Catfish?

Answer

The anal fin morphology (rounded vs. straight margin)

While coloration can fade or vary, the fixed anatomical feature of the anal fin margin—rounded for Channel Catfish and straight for Blue Catfish—remains constant for identification.

What physical feature is considered the most reliable constant differentiator between Channel Catfish and Blue Catfish?
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