"The brown bears are looking for more fish."
Translation:Ruskeat karhut etsivät lisää kalaa.
"Lisää aikaa" is fine too and can be more fitting depending on the circumstance, although "enemmän aikaa" seems to be more commonly used. The subtle difference I failed to articulate earlier stems from the fact that "enemmän" is the comparative form of "paljon" (much), whereas "lisää" doesn't have any degrees of comparison. For this reason "enemmän" is always used for comparisons instead of "lisää", meaning "more than" is always "enemmän kuin", not "lisää kuin", so that would be one situation where they are not at all interchangeable, which had apparently slipped my mind earlier. Aside from that, you're not likely to raise any eyebrows from using them interchangeably, though "enemmän" is more likely to refer to an addition to what one has, whereas "lisää" is more likely to refer to more of what one has already had, so if someone has run out of time and needs more of it, then they would probably be more inclined to say that they need lisää aikaa.