I tried a large soft shell in my tank few years back he was fine with jar but kept biting my catfish's tails because they were lay still so i had to re home him with a mate who keeps turtles
I've found that cichilds will work but they do need to be tough and have the mouths for it big mouthed fish seen to do better at defence in my tank , jaguar cichlid , dovii , bass etc , tried flowerhorns , Midas etc they just get smashed up by the evil jar
i have three good sized endlis, two.smaller.parrots,and a zz flowerhorn. the real issue is the fh getting punked. the jar leaves the rest alone mostly.
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