Herring Fishing is going on along our coast right now and ‘According to Wikipedia the male initiates the process by release of milt, which has a pheromone that stimulates the female to begin oviposit ion. The behavior seems to be collective so that an entire school may spawn in the period of a few hours, producing an egg density of up to 6,000,000 eggs per square meter. ‘So that colour that the water changes to (pale green) is the ‘milt’ which initiates the release of the female spawn.