When anyone says “Fido”, we immediately think “dog”. Where did the name come from, and why is it almost universally thought of as a dog’s name?
I believe it’s because the name “Fido” comes from the Latin for “faithful.”
And it’s spelled “Phydeaux.” 
I believe Abraham Lincoln had a dog named Fido.
Fidelius ? Latin
I’ve been trying to track down instances of dogs being called Fido in history, but have drawn a blank (apart from Lincoln’s). However, in Jan van Eyck’s famous painting The Marriage of Giovanni Arnolfini and his Bride, dated 1434, there is a little dog who represents the fidelity their marriage was expected to involve. It wouldn’t surprise me if there are earlier examples I’ve overlooked.
We aren’t told what the dog’s name was, but the artist was confident it would be a recognisable symbol for the Arnolfinis and their families in the early Renaissance. Most sources seem to confirm that that is the reason why Fido is a traditional name for a dog.
Since the word Dog is the male of the species and Bitch is the female, is Fido therefore always male?
Why are Dogs (Fido’s) faithful and Bitches considered . . uh . . well you know? However, I suppose they could still be faithful.
Why are both male and female called dogs?
The English language is inconsistent in its use of masculine/feminine/neuter terms for animals. In some cases such as dog the same word is used for the masculine and general cases and a different word is used for the feminine case. In others (such as cows, ducks, geese etc.) the same word is used for the feminine and general cases and a different word is used for the masculine case. In others still (such as pigs, whales, elephants etc.) three different words are available for the three cases.
There is no reason I can see to assume that only male dogs are faithful, or that only male dogs are thought of as being faithful. It seems to me that the word bitch carries negative connotations because it is the name of an animal, not because it is female. “Dog” (and the old fashioned “cur”) have been used as insults too.
You’ll have to wait for a better Latin scholar than I am to tell you whether the name Fido is implicitly masculine, but we are familiar with male names in Romance languages ending in -o and female ones ending in -a, so that might influence our decision in naming our pets. FWIW Lincoln’s dog happened to be male.
It is also conventional to consider dogs to be masculine animals generally, presumably because their appearance and general behaviour seems stereotypically masculine.
I’ve also read Fido is from Roman times where it meant faithful. Also I’ve read that the name Hannibal, another famous dog name, has Roman origins as well. When the Romans were angry they’d go kick their dog around a bit, and if they called it Hannibal they could pretend it was the Carthaginian general Hannibal which they didn’t like very much. Very healthy to get the aggression out of the system I suppose – well not for the dog of course ;j .
Rune
Actually, that’s not quite true. Female dogs, both intact and spayed, do have a tendency to be, well, bitchy. It’s particularly not recommended for bitches of similar age, rank, and size to live together because slights are not forgotten between bitches and become grudges, and small squabbles can become serious fights to the death. This is particularly true of several large working breeds.
-Miabella, dog enthusiast and amateur trainer
But is that reflected in the use of the word in general English? We aren’t all dog enthusiasts or amateur trainers are we?
My post was addressed to Miabella.
I have two bitches. I got a 6 lb. Yorkie 14 years ago. Two years later, I got her a 3 lb. poodle for a pet for Chrismas. The poodle beat up the Yorkie rather quickly and we have maintained the alpha dog status ever since. They are inseparable. This must be an odd pair, huh?
everton, I never assumed that you or anyone else here trained dogs or had studied their behavior firsthand. However, it is true that through changes in lifestyle and industrialization, the relationship between dogs and humans has changed drastically. The average person is far less likely to have closely observed the behavior of dogs than back in the days when dogs were our constant working partners. I would maintain that at the time the epithet “bitch” was coined, the average person knew much more about dog behavior than now.
I haven’t done any research into the background of the term “bitch” as an insult, but if you want to learn more about how our relationships with dogs have changed, I refer you to the works of Stanley Coren, Ph.D., Patricia McConnell, Ph.D., and Suzanne Clothier.