For most fish, especially these, at which, similar to pike, 'Fertilization of eggs takes place outside the mother organism, the influence of environmental factors becomes an element that determines the effectiveness of reproduction. Only the survival of the offspring depends on them. In many cases, there is a direct or indirect influence of environmental conditions on biological features, on which depends the amount of deposited eggs.
An example is the age of reaching puberty. From the point of view of reproductive ability, it is, when the young fish, which, as a rule, make up the largest proportion of the population, they start their first spawning early. By repeating them every year, they have the opportunity to produce more reproductive cells throughout their lives.
TABLE 3. Age and length of pike reaching sexual maturity.
Data summarized in the table 3 they indicate, that the age of sexual maturation is not a permanently established trait of pike and it varies between 1 do 6 years. By rejecting extreme values one can assume, that most often the first spawning takes place 2-3 years after hatching. During this period, pikes reach an average length of 30-45 cm, and because both individuals matured in the first are of similar length, and in 5-6 years, should be judged, that the end of adolescence is associated with certain body sizes, while its duration depends on the speed of growth, which in turn reflects more or less favorable environmental conditions for the population. These relationships are well illustrated by the situation noted by Domaniewski (1959) in the Cimlian Reservoir. In the first year after the flooding, excellent conditions were created for the breeding of numerous fish species, providing a rich food base for the pike generation, which hatched in 1952 year. At the end of the first year of life they reached a length of 33-34 cm and in the spring 1953 year 50% individuals have already begun breeding. The rest of them matured at the age of two. Next generations, finding much worse food conditions, they were only 17-18 cm long at the end of the first year, a sexual maturity at the age of 3-4 years.
Some differences in the growth rate of individuals occur in each body of water. Hence the numbers given in the table 3 they do not apply to entire populations. Usually about 10-20% of fish are ahead of the rest or lag behind most of them by 1-2 years. Very often, males mature earlier than females and with smaller body sizes. This is probably due to their slower growth - in this case, a biological property independent of the environment - and shorter life span. Both of these features have an impact on the composition of the breeding stud herd, in which the sex ratio changes with the increasing size of the fish in favor of the females (tab. 4).
TABLE 4. Sex ratio in different size groups of pikes from the Rybinsk Reservoir (according to Zakharova, 1955).
Because the number of eggs deposited during spawning depends on the number of females, the age and size composition of the population is another factor shaping its reproductive potential - a factor, which is not so much defined by environmental conditions, how much mainly with the intensity of the fishing carried out there.