You can eat fish all year round, but you cannot eat every fish year round. Many fish species have an annual biological cycle. They are of excellent quality for part of the year, but for many fish there is a period when they are better left alone; the spawning time.
In order to respect the seasons of different fish species, a calendar has been developed. This calendar indicates when a certain fish species is of good quality and can be eaten without problems. When the fish is of less quality, it is better to leave the fish alone and then choose a replacement fish, there are enough. See the calendar below.
= Badly available
= Readily available