I had a large Synodontis of unknown species a few years back which terrorised my ornate bichir. Each morning i would get up to find large grey patches on the bichirs body where the slime coat had been rasped away but i had no idea who the aggressor was until one night i waited up with a small blue LED torch and watched the tank, soon after everyone else had gone to bed the 8" syno came out of its cave and started to chase the then 12" bichir around the tank before finally trapping the bichir in a corner and started to feed on it slime. The syno was gone the next morning and i havent kept one with my bichirs or ray since.