"There are little red fish."
Translation:Il y a de petits poissons rouges.
Some adjectives go before the noun and others go after.
Examples of those that go before (BANGS):
Age (jeune, vieux)
Number (un, deux)
Goodness (bon, mauvais)
Size (petit, grand)
The adjectives that do not fit in these categories go after. There are a few exceptions, but this is a good general rule. (colors, shapes, origin, material, type, etc.)
The English sentence is plural, there are (meaning more than one) little red fish. If it were singular, it would be written, there is a little red fish.
In English, the plural of fish is... fish in almost all cases*. Certain nouns are the same in the singular and plural forms: a moose, moose / a deer, deer / a grapefruit, grapefruit.
- Fish can be correctly written as "fishes" if the meaning is multiple "species" of fish. This is usually in a scientific context.