Would you expect whitefish embryo cells to continue to divide indefinitely?
No, whitefish embryo cells will not continue to divide indefinitely.
In fact, you could say that no cells divide more than once, because division results in two entirely new cells (the dividing cell ceases to exist). But we can see that this question is asking more about the lineage of cells - will a line of cells continue to divide indefinitely? The short answer is no.
The long answer is that some lineages of embryo cells will divide longer than others. This is because cell differentiation occurs as an embryo develops. The initial few cells of an embryo are totipotent - they can develop into any of the very specialized types of cells that exist in an adult organism. We call these specialized cell types differentiated, some examples are muscle, nerve, bone, and skin cells. There are some types of differentiated cells which do not divide at all - most notably brain neurons. Other types of differentiated cells continue to divide.
So the cells which become neurons will stop dividing sooner, whereas a different lineage of cells might differentiate to a different cell type that will continue dividing long into the animal's adult life. But no, no cells divide indefinitely.