Here is my horrendous mess that is my library. My wife has long given up nagging me to clean it up, and it continues to grow as an ugly sprawl. Only about three-quarters of the shelving you see are fish/fish-related books. The other quarter (to the far left) largely consists of my recreational reading (military history, mostly aviation-related and vertebrate paleontology).
There is another shelf that I keep most of the catfish-only books and theses:
(the first three books in the left of the second photo of this series are an original copy of Bleeker's catfish Prodromus that I rebound, and printed and bound copies of all catfish papers published in Zootaxa for 2003-2006 and 2009-2010).
I arranged the rest of the library geographically (not always strictly adhered to), so here's the Asian section:
Australasian+European
African
South American
North and Central American (which is actually much larger than all but the Asian section)
Miscellaneous (mostly) fish books that I did not/could not place geographically
There were a couple more shelves (all the aquarium fish books) that I did not include, as are the oversized books (e.g. the Smithsonian reprint of the catfish volume of Bleeker's Atlas). My printed reprint collection (two filing cabinets’ worth) is not stored at home, so I didn't include that either.