Your post is very old but someone might stumble on the same question so I'll answer it. As I know (I might be wrong) 'hen' refers to the female bird, so it's translation is 'gallina'. For 'pollo', the correct translation is 'chicken' which refers to the species in general, not to a specific gender. Hope it helps
Exactly. It's similar with fish and is dependant on the context. Fish is the plural form for one kind of fish. So if you have a fising-cutter and you fish for let's say tuna, then at the end of the day you have a lot of fish, just as a farmer has a lot of chicken. If you have an aquarium, then you probably would say you have some fishes there, because they are most likely of a different species. Another example: If you say you saw four fish when scuba diving, that means you saw four individual fish, but if you say you saw four fishes, we might infer that you saw an undetermined number of fish of four different species
Spot on with the fish analogy, but the phrase "a farmer has a lot of chicken" would to me (British) mean meat. I think when talking about the animal, chicken = singular, chickens = plural. As far as the meat goes, chickens would never be used, only chicken which doesn't specify a quantity. It could mean anything from 1 chicken breast to 100 or something
I believe that when walking around on a farm, the word/s used should be "hen/hens", but once cooked and on a plate the word becomes "chicken" whether one or more as the word should not be used in the plural. when the animal is alive eg The farmer has 20 hens. Likewise, the farmer has 2 pigs, but once cooked and on a plate the word changes to "pork", which like "chicken" should not be used in the plural .. So, I intentionally wrote "chicken" as I believe the plural to be incorrect, and Duo marked me wrong! The following time, I wrote "hens" to see whether it would be accepted, but Duo still marked me wrong. Duo can you please review this sentence.
It is true to a point that the names of animals and their respective meats are often different (as you noted, "pigs" vs "pork").
Chicken, however, is a bit of an exception. It is more common to use "chicken" to refer both to the animal and to the meat. (Just note that the plural for the animal is "chickens" and the plural for the meat is still "chicken".)
There is a word exclusively for the meat, "poultry", but it's seldom used, especially in speech.
NB: A hen is just a female chicken; the male counterpart is a cockerel.