In blackbelly you can stand on the right overlook (over where your splatzone is, I think the callout is "snipe") and basically kill everything that comes down the right side. The jet squelcher can hit stuff on the tower, but even the dual squelcher can take out anyone except a sniper coming straight at you or from the ramp. You can basically lockdown the whole side by yourself.
I love the DS in walleye and piranha pit as well. Both are fairly open maps with a lot of room to maneuver, which is great for the DS. You have to be more mobile on these sorts of maps, pressuring when you need to and retreating at other times. You are also sort of a backline fighter, so you have to be aware of flanks (hello echo) and reposition to cut off enemies.
I honestly hate arowana because I often find myself in close quarter situations and while the DS can be ok in those situations, if you go 1v1 vs a tentatek, nzap, jr, splash/sploosh, or even aerospray at close quarters it will result in your death. I tend to like burst bomb weapons in that map because I can be close up or have range depending on the situation. Same is also true for Flounder - too much close quarter combat. Not that the DS can't be good on these maps, because it has the versatility, but I tend to use something else.