Herring - Life Cycle

Life Cycle

At least one stock of Atlantic herring spawns in every month of the year. Each spawns at a different time and place (spring, summer, autumn and winter herrings). Greenland populations spawn in 0–5 metres (0–16 ft). North Sea (bank) herrings spawn at up to 200 metres (660 ft) in autumn. Eggs are laid on the sea bed, on rock, stones, gravel, sand or beds of algae. "...the fish were darting rapidly about, and those who have opportunity to see the fish spawning in more shallow water ... state that both males and females are in constant motion, rubbing against one another and upon the bottom, apparently by pressure aiding in the discharge of the eggs and milt" (Moore at Cross Island, Maine).

Females may deposit from 20,000 up to 40,000 eggs, according to age and size, averaging about 30,000. In sexually mature herrings, the genital organs grow before spawning, reaching about one-fifth of its total weight.

The eggs sink to the bottom, where they stick in layers or clumps to gravel, seaweeds or stones, by means of their coating mucus, or to any other objects on which they chance to settle.

If the egg layers are too thick they suffer from oxygen depletion and often die, entangled in a maze of fucus. They need substantial water microturbulence, generally provided by wave action or coastal currents. Survival is highest in crevices and behind solid structures, because predators feast on openly disposed eggs. The individual eggs are 1 to 1.4 millimetres (0.039 to 0.055 in) in diameter, depending on the size of the parent fish and also on the local race. Incubation time is about 40 days at 3 °C (37 °F), 15 days at 7 °C (45 °F), 11 days at 10 °C (50 °F). Eggs die at temperatures above 19 °C (66 °F).

The larvae are 5 to 6 millimetres (0.20 to 0.24 in) long at hatching, with a small yolk sac that is absorbed by the time the larva reaches 10 millimetres (0.39 in) is reached. Only the eyes are well pigmented (a camera works only with a black housing). The rest of the body nearly transparent, virtually invisible under water and natural luminance conditions.

The dorsal fin forms at 15 to 17 millimetres (0.59 to 0.67 in), the anal fin at about 30 millimetres (1.2 in)—the ventral fins are visible and the tail becomes well forked at 30 to 35 millimetres (1.4 in)—at about 40 millimetres (1.6 in) the larva begins to look like a herring.

The larvae are very slender and can easily be distinguished from all other young fish of their range by the location of the vent, which lies close to the base of the tail. But distinguishing clupeoids one from another in their early stages, requires critical examination, especially telling herring from sprats.

At one year they are about 10 centimetres (3.9 in) long, first spawning at 3 years.