Learn Turkish: Uzunca yüzgeci ile yüzen balık yosunda saklanıyor. - The fish swimming with its rather long fin is hiding in the algae.

The suffix -ca (or -ce, -ça, -çe) softens or approximates an adjective. While uzun means "long", adding -ca makes it mean "rather long" or "long-ish". It tells us the fin is on the longer side, but not necessarily exceptionally long.

Why does the word for fin, yüzgeç, become yüzgeci here?

We need to add the third-person possessive suffix -i to mean "its fin". When a vowel suffix is added to a word ending in the hard consonant ç, it softens to c. This makes pronunciation smoother.

What does the -en suffix do in the word yüzen?

The -en suffix is a subject participle. It turns the verb yüzmek (to swim) into an adjective that describes the fish. You can translate yüzen balık as "the swimming fish" or "the fish that swims".

Why use saklanıyor instead of saklıyor for "hiding"?

The root verb saklamak means "to hide something else". Adding the -n suffix creates the reflexive verb saklanmak, which means "to hide oneself". Since the fish is hiding itself in the algae, we must use saklanıyor.