is there any special meaning behind it? a symbol for the outside of the city (which seems to be surrounded by water)?

I think it has some wierd meening - that fish is Lathimeria (my spelling is wrong but it is like that ^^) - that fish is a "living fosile" - meenig that fish is still living today in the same shape for - i don`t remember correctly but for aprox 50-100 million years. They catched one in 1974 - um, near the coast of Mexico - or it was India ... um... sorry don`t remember. But that is the wierdest living fish - by shape older than anything else...
Meening - don`t have a clue it could be infinite meanings... Like thing that never changes... (*god,now I`m talking craps ˇ-ˇ*)

Btw. in chapter one, page 2 or 3 when Killy is passing with that boy there are two MANTA RAYs flying above them - hologram or he eated too much acid? ^^

Well I realy didn`t get it if it is connected with some of the characters... when I think of it maybe it represents humans - like living fosiles on the Earth, that they are long lost but still here... or something like that...
In OVA Log 01 there is allso image of Lathimeria on the walls in blue light...
... or maybe it meens nothin, is just for show...

Latimeria menadoensis


So - the fish... ^o^
http://www.fishbase.org/Summary/SpeciesSummary.cfm?id=53783
or
http://www.fishbase.org/Summary/SpeciesSummary.cfm?id=2063

Expanding on what ergates said, I think that Cibo is also somewhat inspired in Gadfium from Feersum Endjinn, but I wouldn't know just how much, since I haven't gotten very far into Great Sky River yet. I could only get a hold of it in Spanish and even though it's my native language I hate reading books in Spanish; especially books that where not originally written in Spanish. I'm trying to make an exception but it just seems so lame when translated; however, I'm stubborn so I'll finish it eventually.