Iam a bit curious why exactly Kizaro decided to let Arlong go in the end.
Afterall Arlong was a known human-killer.
So one possibility is that he made some kind of deal with Arlong which guaranteed him his freedom.
Arlong wouldnt work for the humans, but going against the royal family(especially Otohime) would also fit into his own plans. That he can
t be responsible for Otohimes death was already said(because at that time he was already disbanded from the sun-pirates), so it could have something to do with Kizaru wanted to undercut the sun-pirates with a little help from Arlong.
Arlong already doesnt like in which direction Jinbe
s believe goes, so that wouldn`t be unimagenable.
Maybe Kizaru planned to use the sun-pirates to contaminate the fishman-reputation even more, to get even more reason to fight them.
Jinbe was so forced to disband Arlong from the sun-pirates to carry Fisher Tigers will of having a non-human killing piratecrew, while Arlong followed his believe non the less.
So Jinbe reacted against Kizaru`s main plan(or the plan was from the WG) and thats why they decided to control them with giving Jinbe a spot as a shichibukai.