Probably seems like a quite a lot, but I've been collecting fish books since the late 1950s.
Many were lost along the way, and even though many of the names are/were in some, outdated, much of the info still stands the test of time.
I especially like evolutionary theory's and feeding info in Ad Konings "Cichlids of Central America", geographic info in Staeck and Linke's "American Cichlids Large", Weidners " S Amer Eartheaters", Loiselles "The Cichlid Aquarium", and "the Endemic Cichlids of Madagascar" by Nourissat and de Rham, just to name a few.