I always thought it might have something to do with how they hunt in nature, I would be interested to see someone set something up like a archer fish tank and see if the arowana developes dropeye.
I've owned many jardinis and leichardtis (Australian arowanas) for around 10 years, aswell as some of my friends, and have NEVER repeat NEVER experienced drop-eye... or even seen it for that matter amongst the two species.
I keep my asian aro in my pond. I honestly think its because of the constant looking down. I plan on building a fence and letting loose crickets on the above water plants to let him hunt wild.
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