Yeah if you want something you can keep in something as small as a 40 breeder for life that's as mean as a snakehead I highly suggest red wolf, erythrinus erythrinus, or if you can rind one they say white tip erythrinus are meaner. Along with kesselleri (not sure if I spelled that right). In a 75 you could probably do 2 wolves and couple smaller bichir with proper filtration. Plenty of hiding spots and decor to break sight lines if you try more then one wolf. Keep a divider ready just in case especially if ones a bit bigger
As far as temperament mine have dittoed the above post other then in terms of activity, mine is swimming about a lot perching itself in random places. They go after live worms real quick haha but they sit and wait for a live fish to come near to eat. My Ornate bichir would always just let my red wolf chase feeders basically into his mouth lol
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