Spawning generally takes place be-tween early May and late July, and is primarily dependent upon water tem-perature. Usually, this needs to be in excess of 17°C (62.6°F) to stimulate the wild carp into spawning. There is strong evidence to suggest that spawning is often prolonged over a period of several days, or even weeks although whether different fish are involved, or the same fish makes repeated efforts, is not clear.
The eggs are usually shed in shallow water, on soft aquatic vegetation. In deep ponds and lakes, with no shallows, the carp has been known to come close to the margins to spawn on overhanging vegetation, and even on fibrous roots and branches. The female is generally accompanied by two or more males, and the actual spawning is carried out very energetically so that the splashing of the fish may be audible over considerable distances. The small, translucent-grey eggs, c 1 mm in diameter, swell and are sticky 1 on contact with water, becoming <o attached singly to whatever medium % the carp are spawning over. The o amount of eggs carried by the female is directly related to her size, but may also vary according to environmental factors. The proportion by weight of eggs in a female wild carp, just prior to spawning, is less than in the cultivated ‘King’ carp variety, amounting to approximately 10 – 20% of body weight, while the roe of a female ‘King’ carp can represent up to one third.
The eggs hatch in 4 – 8 days, depending on the temperature, the newly hatched larvae having a yolk-sac on which to feed initially. The larvae are able to attach themselves to plants, or will lie on the bottom, before floating to the surface after two or three days to fill their swimbladders with air. They then become free swimming, and feed on microscopic algae, rotifers and water fleas. Growth is variable and depends mainly on the amount of food available and water temperature, but other factors, such as the oxygen content, also have an effect.