Find the actual similarity rule
Fish Merge describes combining similar items in an underwater setting, with colorful fish as its theme. Similar can mean different things across merge games, and this listing does not define the legal pairing rule. Look for the game's explanation of which items can combine. An apparent resemblance in color or shape is a clue to examine, not proof that two fish belong in the same merge group.
Track one lineage at a time
Once a valid combination is established, follow what it produces. A useful practice note connects the input items with the resulting item, without assuming the next recipe follows the same pattern. If several possible combinations exist, focusing on one visible lineage can make progress more understandable than triggering unrelated merges rapidly. The description cuts off before explaining the wider progression or any final collection goal.
Judge order through the board
Mouse and touch are listed, but drag behavior, board size, and placement restrictions are not. Use the actual interface to determine whether order or space matters. If the game gives you a constrained field, compare how two legal merges affect that field; if it does not, do not import a space-management problem from another title. The soothing underwater presentation can be a preference, while the combination rules remain the practical basis for play.