You came pretty close to answering the question. :)

That book was reviewed on Guppylog after a visit to Borders. But much as one might like, they can't buy every fish book they read or scan through at the bookstore. Borders according to a recent business section article in the paper is in trouble. Maybe it would have been better to have bought yet another general fish book. ;)

Scientific names get changed often enough. And sometimes they get changed back again, something that is even more confusing. But popular names can also be confusing. Some North American fishes may have a half-dozen to a dozen regional popular names and that is just in the US, not counting Canadian and Mexican names. Shops, wholesalers and fish farms sometimes get clever and coin new common names or borrow an old name for a another fish. One magazine publisher used to be notorious for suggesting "popular names" which no one else had ever used. There are a lot of nominees for a black barred livebearers. :)

The other night, on the correct premise that browsing a book I was familiar with would help me go to sleep, I picked up a copy of Innes's venerable Exotic Aquarium Fishes. The first edition of that book came out 70 years ago! My copy has got to be a garage sale or library sale special which is 40 years old. (The post 1970 TFH editions plugged some more "recent" color images in there and despite their intentions, made something of a mess of that work.

Once one sorts through the name games, Innes' book (once considered something of a Bible of the hobby for a couple generations of aquarists) is still surprisingly useful. And curiously enough, scientific names in there have fallen out of favor and with recent DNA work may be brought back. Dr. Donn Rosen, a livebearer specialist "lumped" a lot of the livebearer in the genus Poecilia in the 1960s. That somewhat dated Innes' book, in part, reflects the hobby from before World War II! Back then not so many fish species were imported to the US from Africa or Asia. A lot more wild livebearers from relatively accessible Central America (or southern North America) were imported for the aquarium market.

Many of those are not so common in the hobby and almost never found in the shops. ALA activities, auctions of the larger, more active aquarium societies, the few local livebearer clubs (New England, Houston, the Pacific northwest...) and Aquabid are among the more likely sources of those fish.

I probably should know this, but what part of the country (US or otherwise) do you hail from? This isn't to smoke out your specific address, because that is not our business, But as a example, I live the Chicago area or in the southern 'burgs of Chicago.

With Rosen's work, guppies were moved from Lebistes to Poecilia. The fishes of the Genus Limia (warm water livebearers from the larger Caribbean islands) were also moved to Poecilia. Even the Mollies were moved from Mollienisia to Poecilia.

Some years ago a Cuban scientist by the name of Rivas published a response to Rosen works, contending that Limia was indeed a genus in good standing and (something important to fish taxonomists or systematic people) probably descended from a common ancestor. That has been pretty much accepted by scientists and hobbyists. To my bemused surprised, a couple of livebearer posts lately have begun again referring to Mollienisia and Lebistes!  This can cause one to start making b-b-b-b-b noises.

A lot of changes have been talked about at the last couple of ALA conventions and I missed out on them, as I will (sigh) again this year. I always thought that this species and genus stuff was set in stone. Boy was I wrong!

Certainly genus can be a matter of opinion, hopefully based upon fairly informed reasoning. But the data which goes into defining what fishes are in a genus include a number of things. So if two fishes will not produce viable offspring past two generations as a hybrid, they are probably different species. Even behavior, though this is quite controversial, may be considered in deciding if two populations of fish are the same species or different. If their pattern of chromosomes, the size of certain chromosomes or the number of chromosomes are different, they are likely different species. DNA differences (in the portions of the DNA which vary from species to species) can indicate different species. Geographic separation also can indicate that different fishes are different species. (An interesting side-line here is that the presence or absence of related fresh water fishes can be used to help trace the ballet of Continental drifting.)

For instance: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WNH-456JS6R-37&_user=10&_rdoc 1&_fmt&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVer sion=0&_userid=10&md5=45c71ea0f04adfa1e684e6e41e2dda44

http://links.jstor.org/sici?sici=0039-7989%28198412%2933%3A4%3C428%3AFFABOC%3E2.0.CO%3B2-H&size= LARGE&origin=JSTOR-enlargePage

By the way, even though Innes sorted through a lot of imported livebearers, he didn't list any of the common names as a Black-Barred livebearer. ;)

(A black-barred livebearer is like having a gray Gambusia, a silver minnow or a blue killie.)

Several of the scientific and popular names do remain the same though. Innes' merry widow, Phallichthys amates, still goes by both of those names.

Sometime, I'm going to take a couple of days and make lists of all of the killies mentioned in certain old books. (There are several recent killie books and sites of use in reliably checking that stuff out.) Then we'll list what those fish are called today, for the benefit of hobbyists who are quite rightfully confused and bewildered by some of the name changes. I've got a couple of sites in mind where those could be posted to, so other aquarists could benefit from a few explanations and so that still others may correct my mistakes and the inevitable changes which will arise in the literature.