268 SALMONID^ OF BRITAIN. 



which is, provided the mortality during incubation is not great, Avhat is it among 

 the alevins, springlings and yearlings ? In the first lot (laid down Nov. 11th, 1884) 

 there was a great deficiency of vitality among the alevins, which suffered extensively 

 from dropsy of the sac, about 10 per cent, dying during the first month and another 

 20 per cent, subsequently before June. A similar result occurred in the second lot 

 (laid down Nov. 29th, 1883) wherein in fact by August, 1884, only 100 remained 

 alive. 



Next we see (Dec. 9th, 1884) a few eggs of a salmon grilse which it was 

 attempted to fertilize by means of the milt of an adult Lochleven trout, and here 

 doubtless the same mechanical difficulty already alluded to would take place, the 

 number of eggs lost during incubation being 62 per cent ; only about one-half 

 having been impregnated. 



Passing on to still smaller eggs, as of the American char, the attempt to 

 fertilize them (Nov. 29th, 1883) with even young salmon was a great failure, as 

 many as 93 per cent, being lost during incubation, in fact all but 21 out of 1000 

 appear to have escaped impregnation. 



In the next two experiments (Nov. 15th, 1882, and Nov. 29th, 1883, zebra 

 hybrids) eggs of Lochleven trout were fertilized by American char and here no 

 mechanical difficulty could be present, and the deaths during incubation were from 

 15 to 17 per cent., while comparatively very few were lost from want of impregna- 

 tion. With two such distinct species as a char and a trout, crossed as described, 

 we find deaths and deformities due to hybridizing, in fact to some physiological 

 not mechanical cause ; while as the parents were both of pure breeds and no 

 reason existed to suppose that the generative organs of either were affected, 

 this would seem to point out that crossing these two distinct species was calculated 

 to occasion deformities or monstrosities in the resulting offspring. 



Similarly fertilizing American char eggs Avith milt from the Lochleven trout 

 (Nov. 15th, 1882, leopard hybrids) the mechanical difficulty would seem to again 

 occur and the mortality during incubation was about 32 per cent, or double what 

 took place in the preceding cross. As might be anticipated the physiological 

 deleterious cause was likewise present in this instance, consequently deformities 

 were numerous. 



If we, however, pass on to a cross made between a male American char and a 

 British char (Nov. 15th, 1882, struan hybrids) we see an almost intermediate 

 condition. Here we can hardly suppose that the mechanical difficulty would 

 be present, yet the mortality was as great as 23 per cent., pointing to the 

 physiological or pathological question, but the young were not so malformed as in 

 the preceding crosses. But it may be a subject that has yet to be solved as to what 

 is the relationship between the British and American chars ? 



This brings us to the consideration of are hybrids fertile ? and in the preceding- 

 experiments it has been shown that they are. But mere possibility of fertility 

 from the males or females of these hybrids, however interesting physiologically, 

 is not so much so to the fish-culturist and riparian proprietor who wishes 

 to know the amount of fertility which might reasonably be anticipated, and 

 through how many generations ? Also whether fertility decreases with increased 

 hybridization ? 



Doubtless the amount of mortality among the eggs of hybrid Salmcmidce is, as 

 has been shown, very great, but the age of these fish is one factor that has also to 

 be taken into consideration. 



First as to the interbreeding of struan hybrids, in the first year when this was 

 carried out (Nov. 12th, 1884) or when the fish were 21 months old, the mortality 

 was over 96 per cent, of the eggs, in fact out of 146 eggs only six hatched. On 

 December 6tli of the same year this cross was again made, but the mortality was 

 over 91 per cent., and of the 50 which were hatched only one lived ; these fish 

 had no stamina. 



Breeding these struan hybrids among themselves when a year older (33 months 

 old) gave the folloAving result (Nov. 25th, 1885), a mortality of 83 per cent., but 

 the deaths among the young, although considerable, did not reach to what occurred 

 the previous year. 



