Yes, it is. But the hump comes too late to be useful as the fish are already quite big and have reached sexual maturity when other gender clues, like color, size and reproductive tube become obvious. A big hump is definitely a male, but some poor quality males never develop a hump any bigger than an old female.
I disagree with the poor quality male statement? It is just largely influenced by the fish's genetics and somewhat the environment. Some green terrors develop the nuchal hump and others simply do not develop a nuchal hump...
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