This is a video about a zander in the Brechtsee in Germany.
According to the Baltic Sea Portal:
The diet of [great] cormorants [in Finland] consists predominantly of the most abundant fish species of shallow waters. The amount of fish needed by a cormorant is about a half kilogram per day. Three fourths of the diet during the nesting period consists of economically valueless species, such as roach. Of economically valuable species, perch makes up one fifth of the total amount of the diet, whereas the proportions of Baltic herring and zander are less than five percent.
Though the proportion of zander is small in the cormorants’ diet, this fish may mean life or death for a great cormorant.
Zanders are big fish. The biggest ones are too big for a cormorant to gulp down. If it tries so nevertheless, the zander may get stuck in the cormorant’s gullet; and the cormorant may die.
According to Dutch daily NRC Handelsblad of 12 February 2009, page 18, there is a maximum height and circumference for fish beyond which cormorants cannot eat them: 7.4 centimer height, 23 centimeter circumference. Which corresponds, for zanders, to 48 centimeter long. Height and circumference are more important than length.
Atlantic herring mega-shoals: here.