How many eggs do sea trout produce?
There is quite a lot of variation, although the theoretical average figure of 800 eggs per pound of body weight has been cited in the past. Overall, British and Norwegian stocks of sea trout have similar levels of fecundity, but French sea trout produce many more eggs for the same body size. It is unclear how much of this natural variation is inherited and how much it depends on early growth rate, overall age and levels of feeding at sea. In Scotland, River Ewe System (Wester Ross) sea trout contain significantly fewer (but larger) eggs than River Earn (East Coast) sea trout of the same size. Unlike in birds, egg size in trout increases with overall body size, but it also increases with age, independently of body size. So, large, old sea trout produce the biggest eggs, while smaller, but fast-growing, young sea trout have lots of small ones. The early survival prospects of fry may be positively linked with egg size, but many other factors come into play in deciding their fate.