Define aggressive... what are you thinking? Polys are actually pretty mild in comparison so sometimes can be bullied by aggressive fish like cichlids for example
Delhezi don't get big, water cow goby are said to get up to 17" in which case it'd consume a del. I'd say go for larger species with that goby, they're greedy. By aggressive I assume you mean predatory, you can try a number of catfish like sun cats, 4-line pim, ornate pim, bolt catfish, maybe a vulture catfish if you upgrade, maybe Asian USD catfish, species of synos. For characins, you can do an odoe, maybe a species of wolffish like mala, curu, gold, though you'll need an upgrade for those, depending on what species of bichirs and whether or not you get the goby, maybe even erythrinus. Maybe some pink tail chalceus or Apollo sharks like Vancouver has. SD, barbs, as long as you don't keep plants. Oh and the goby will also need an upgrade. A 180 would really open up your options....
I've got a delhezi a senegal and 3 ropes in my 120g, always plenty of activity in the tank, the delhezi's look great and imo you couldn't go wrong with one of them
