Death fish, vampire fish and robot fish will be no problem to replace.  Just get this mod here from Mod the sims.  It allows you to buy all types of fish at any number. 

http://linna.modthesims.info/download.php?t=343257&goto=nextoldest

If you have the unlucky trait, you can cheat death.  Sort of speak..  Live only to die again to amuse the Grim Reaper.  In that only way that it is useful.  Charismatic and friendly sims build friendships faster.  Snobs are good at keeping themselves clean.  Ambitious and Workaholic sims seem to climb the job ladder faster than other sims.  Ambitious sims sometimes have a wish to raise to the next level of their skills.