"She is eating my fish."
Translation:Elle mange mon poisson.
that might help(sorry if you already know it):
mon is when the object you're talking about is masculine and singular.
ma is when the object you're talking about is feminine and singular.
mes is when the objects you're talking about are plural.
The original sentence "She is eating my fish" is vague. Both "mon poisson" and "mes poissons" should both be correct (and currently are) if the context used for "fish" is both singular and plural. However it's really difficult to determine whether the program is asking us to be literal or otherwise with our interpretation of the original sentence when there doesn't seem to be any consistency across the program for either literal or subjective interpretation. I'm at least hopeful that as Duolingo grows and becomes more popular that little irregularities like this will be ironed out!
What the! First time I answered this question, it says both Elle mange mon poisson and Elle mange mes poissons were right. Second time, it marked me wrong for choosing both. Now on the third time, i chose just the Elle mange mon poisson option and still wrong. Will I ever get this right!?
The collective plural of fish is always fish in the UK; in the US, fishes is encountered as well. When referring to two or more kinds of fish, the plural is fishes.
Contextually, it was not defined if it were singular or not so if you are talking semantically you are correct, but practically, it's kind of vague.
As I understand it, ma is the singular feminine, while mon is the masculine singular, and before a vowel. They all translate in English to "my".
Eg. Le robe = the dress (feminine) Ma robe = MY dress
Le gant = the glove (masculine) Mon gant = MY glove
However, if the noun begins with a vowel, you always use MON, even if it is a feminine noun.
Eg. Une orange = an orange (feminine) MON orange = MY orange.
If the plural form is used, you use MES
Mes robes = my dresses mes gants = my gloves mes oranges = my oranges
(Hope this helps a bit. I'm sure there are exceptions though!)