Compressiceps stay small ... smaller than the convicts would get. While I would feed mine eggs and convict fry only a few days old (they have small mouths, the convicts were in their own tank) a pair of convicts would be able to defend their fry from the pike rather easily.
A compressiceps will kill fish up to about an inch long, even though it can't swallow them ... it will crush the head and slurp out the goodies ... watched this happen to tetras I knew were way to big to swallow. :x
They don't need live food ... I only used the convict eggs and fry to condition the pair I was trying to breed. Normally I gave them frozen food ... bloodworms, daphnia, glassworms and mysis shrimp.
If you want something that'll hunt fish, you'll want a bigger pike. Most of the dwarves are specialized feeders on dwarf cichlid fry only, won't even go after apisto adults (as food at least).
o ok i can only stay small now so one Crenicichla compressiceps and what else could i do in ther cihild wise is there a nother dwarf pike that it would live with...becasue you said the dont like each other
I kept mine with dwarf acaras ... but it was a much larger tank. The pike mostly left them alone except at feeding time or if they got too close to his cave. Stay away from aggressive cichlids, ironically enough, that little pike killed a jack dempsy much larger than it becuase the jd picked fights. The dwarf cichlids didn't, so the pike left him alone. At most I would only add one curviceps or a larger apisto pair like caucs ... though in a 20 long/29 personally I wouldn't add another cichlid, just not enough floorspace with the dwarf pike.
The only way to get a confirmed pair would to be buy them as a pair, which would be expensive or get a group of like 10 in a HUGE tank and let them pick a pair. Compressiceps are easy to sex, but throwing together any male and female will not usually work.
Larger cories or brochis are good to clean up the left over frozen food, larger tetras like lemons or pristellas would be good ... pikes aren't that active, just kind of hang out near their cave.