On shabbos the freezer door wouldn’t close because there was some frozen fish blocking it from closing. Can the fish be removed to another freezer or moved? If not it can spoil the other frozen food in the freezer or even the freezer itself?
Frozen fish is muktzeh machmas gufo (it is not a utensil, and has no potential use on Shabbos; see Shulchan Aruch, Orach Chaim 308:32), and therefore may not be directly moved even if its place is required.
However, it can be moved indirectly, because moving it is for the sake of its place, or moved by pushing it with a part of the body (based on the leniency of the Mishnah Berurah (308:13) whereby it is permitted to move a muktzeh item with one’s body).
One option is therefore to push it deeper into the freezer with one’s body (the forearm, etc. can be used).
Another option is to move the fish indirectly, i.e. by means of something else (an item can be placed under the fish). Once the fish is moved (indirectly) to allow the freezer to close, it can be transported to the other freezer (see Mishnah Berurah 266:35; 308:12, based on Tosafos Shabbos 308:9; see also Biur Halachah s.v. yachol that points out the safek of Rabbi Akiva Eiger on this matter).
The above option is not permitted according to all opinions (the reason being that it is possible to do ni’ur, to simply shake out the fish, which will allow the freezer to close; the act of moving the fish is therefore for the sake of the muktzeh fish; this depends on a dispute between the Mishnah Berurah and the Chazon Ish (see Magen Avraham 310:10, based on Bach; see Rabbi Akiva Eiger 309), and the first option is therefore preferable.