For me its the payara species Scomb. and redtail barracuda's. I have tried 6-8 of the scombs and 4 of the cuda's and the never made it more than a month. I don't think I am alone here as i see more and more people calling the scomb-the 2week scomb.
I'v never really had a problem keeping fish alive... it's resisting buying that monster to put in the tank that is going to eat them all.
No but seriously, I have no problem keeping any fish that I bought alive (and healthy). I seem to have a problem with water dragons though. I have owned 4 of them and every one dies before it gets over 5"
i have no idea where my neon's dissappear everytime i get some.....they just vanish...difficult to believe the tank mates would eat them [guppies,small mollies,platies and glowfish ]