How do environmental changes like sudden temperature fluctuations affect older, veteran Arowanas?

They can severely destabilize the older fish whose systems have adapted to equilibrium.

As an Asian Arowana ages, its body systems become highly attuned to the long-standing equilibrium established within its environment, a process that takes decades. Consequently, external stimuli that a younger, more adaptable fish might easily tolerate—such as a minor shift in tank location or a slight temperature swing—can have a disproportionately negative and severe impact on a veteran fish nearing or exceeding twenty years. Managing transitions becomes exceedingly delicate for older specimens because their established physiological stability is more easily disrupted, potentially leading to serious health consequences that they may not have the reserves to recover from.