Jordan Sargent has a remarkable photograph taken by Ingolf Kristiansen off the coast of Norway. Apparently a large number of herring were swimming close to the surface when a gust of cold wind froze the water near the surface, trapping the fish in place. I found this surprising because the phase change from water to ice is not instantaneous and one would think that as it happened the fish would go lower where it remains as water.
Very rapid instantaneous freezing is possible when water is supercooled. i.e., stays in the liquid state below the freezing point. This can happen when the water in a container is undisturbed as the temperature drops. Sudden motion can then cause it to rapidly change its phase into ice. Below is a video that shows it happening for a regular bottle of water.
Note how the water freezes from the top down. I did not think that fish freezing could be caused by supercooled water because the fish were swimming around and the water is being constantly disturbed.
The other possibility I can think of is that the oxygen level in the water lower down was so depleted by the cold that the fish had no choice but to stay near the surface, even as the water froze around them.