Silvers are the biggest. They are also the cheapest. And most prone to drop-eye. You MUST have a lid covering every square inch of surface area. The lid needs to be supported with something heavy or ducktaped. They jump all the time in the wild for insects. Drop-eye is when the muscels in the eye freeze and they can't move. Pointing straight down. It looks really bad and I've never heard of a captive raised silver over 20" not having it. I mean your dealing with a 99.99999% chance of him getting it. Enough get it that most people will just round the numbers to 100%. Because its pountless to give somebody this false hope. If I liked the fish a lot I probably wouldnt mind it. Just me though. but I'm just giving u a heads up. That's all. Jardini are also very agressive and generally intolerant towards tankmates. Arowanna are a very demanding fish so be prepared. Not your typical 'fish-in-a-bowl'. Jardini 'can' get drop-eye its just much much less common. Chances are on your side he wont get it.
Hopefully this helps
Its a Jersey Thing
and the ducktape part. i keep a big heavy rock on top of all lids.