hi yall, i just have some general questions about needlefish. im considering gettin some, when my other fish get to big for them to be eaten

has anyone here eve kept them? i know they get a little bit big, so i'll need a decent sized tank.
how agressive are they? my fish are pretty peaceful, so im not worried about the needlefish gettin picked on, but visa versa.
anyway, i'd really just like to hear about any advice or experiences yall might have
thanks yall
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29 gallon
1 male convict, 1 female convict(breeding pair), about 50 babys, 1 albina chocolate plecos
no plants, about to give away convicts and turn over custody of tank to my girlfriend.
20 gallon
1 or 2 african leaf fish(they dissapear)

, 1 striped peacock eel, 1 rapheal catfish, 1 rubberlipped plecos, 2 convict fry, meant as feeders never eaten