VALUE OF NORWEGIAN LAKES FOR FLSII CULTURE. 593 



is placed likewise at much too little ; both parts in all likelihood ex- 

 ceed the probability. 



For each fish that one Avill calculate to capture in the fifth year of 1 

 kilogram in weight I assume that one ought to find in the water (450 + 

 550 + 700+ 1,000) di^ided by 400 = 7 fishes of younger ages, as likely 

 the fishes of the oldest class, which may be too small, will be compen- 

 sated for by younger individuals of greater weight from year to year. 



II one estimates now for each fish, without regard to age, a surface of 

 l.o square meters or 1.5 meters long and 1 meter wide, or for each fish 

 of every age a surface five times as great as M. Bouchon Brandely adopts 

 for four years old, it should probably be assumed that no crowding can be 

 expected to take place ; because a lake of the size mentioned may gen- 

 erally be considered to have an average depth of at least 5 meters ; each 

 fish, small and great, thus obtains 7.5 cid)ic meters or 7,500 liters (Potter), 

 or twenty-five times as great cubic space as that considered sufficient 

 for adult fish by M. Bouchon Brandely. In a water area of 3 hectares, 

 which equals 30,000 square meters, can also be estimated 20,000 fish of 

 all ages, and of these one-eighth, or 2,500 adult fishes over four years 

 old, of a weight of 1 kilogram and upM^ards. There is, as remarked, nat- 

 urally nothing to prevent taking fish of younger age or smaller size. 

 Many will perhaps even prefer fish of half this weight. I hold, however, 

 to the size and age mentioned essentially so as not to estimate the profit 

 too high and attainable in too sliort a time, at the same time, because ac 

 the age indicated the fish may be considered fully mature, as after this 

 age the common trout, which alone I have here in mind, increases more 

 slowly in size and weight, and also becomes less i)rofitable. 



According to the calculated decrease, from year to year, to a number 

 of 2,500 fishes of over four years old, will correspond a number of the 

 youngest class of about 0,500 individuals in the first year which must 

 be liberated in the water to compensate for the decrease of the captured 

 adult fishes. But it is not enough only to calculate on the hatching out 

 of this number. The most delicate age from the time the hatching out 

 can be considered completed with the absorption of the egg-sack until 

 autumn, is, according to all experience, the most dangerous time for the 

 young, since the death rate is greatest, and here it is assumed that the 

 X)onds or basins procured for the rearing of the young during the first 

 summer are not likely to be of the best kind, and that the attention, at 

 all events, at the beginning, is incomplete ; as a result of this, the death 

 rate must be estimated comi)aratively high. If one place this decrease 

 at about 50 per cent., which will likely be estimating it high enough, 

 and add at the outside about 10 per cent, for loss during the hatching 

 itself, there will be required at the highest 10,500 eggs each year for 

 hatching. 



It is probable that this quantity of eggs will yield a larger number of 

 fish than is necessary for obtaining the stated number of adults ; but 

 this can likely involve no harm, because if it should be e^ident that the 

 38 F 



