Clue: Turkish commander runs with a fish in jelly (4-4)
Answer: AGAR-AGAR
Explanation: Definition: jelly
AGA + R + A GAR. Not difficult, but I like the way the repeated word is split up in two different ways. Agar-agar jelly (also called just agar jelly) is used as a growth medium for bacteria etc in biological experiments, but also has some (mainly Asian) culinary uses