60 PHYSOSTOMI. 



brook trout. Sterility, however, does not appear to normally exist in these so-called 

 hybrids which raises a suspicion that we may be dealing with developing varieties 

 and not with hybrids at all. And as these forms have facilities for returning to 

 the sea, did they desire to do so, we are led to ask whether some of them may not 

 be changing their conditions of life, and as a result developing structural 

 differences, or even whether they and the brook trout can be really distinct species.* 

 At Sir James Gibson Maitland's fish farm at Howietoun, some of the young of the 

 Loch Leven trout take on cannibal propensities, and if small their colour is yellow, 

 their teeth become abnormally developed, and they grow very rapidly. It is thus 

 evident that under certain circumstances we may find trout provided with stronger 

 teeth than is usual in the species. If we look at examples of sewin retained some 

 time in fresh water ponds we see their pectoral fins more pointed and usually 

 longer than in their sea-going relatives. This leaves chiefly for consideration 

 whether these silvery forms with black X-shaped spots could, under any conditions, 

 assume the deep coloured and spotted appearance of the common brook trout, or 

 anything approaching to it. 



At Howietoun this general yellow tint shows itself when the fish has arrived 

 at about its fourth year, but is also affected by seasons and food. When fed 

 upon horseflesh they remain of a gray colour, if clams (Pecten obtusata) are given 

 they assume the yellow colour. Overcrowding large ones, or such as are 4 lb. or 

 upwards, induces rusty spots ; if the numbers are reduced, and vegetable food 

 given, as lilies and clover, they became gray ; while silvery scales are a sign that 

 they are in their primest condition. The young parrs may retain red spots up to 

 eighteen months old, but such are almost absent between that age and three years. 

 Red spots on large fish are mostly perceived in examples intermediate between 

 kelts and trout in their primest condition, but occasionally they are present 

 all the year round. During the breeding season the males, if healthy, assume a 

 brownish orange colour, or if from considerable depths a darker tint, while the 

 females are golden or orange red. It consequently appears that conditions of 

 health and changes of food may occasion alterations not only in the superficial 

 colour of these trout, but likewise in their more deeply-seated colour spots. 



The foregoing point out that as the colour of Loch Leven trout may be altered 

 by food and conditions of health, there exists no reason why the same changes 

 may not occur among examples of sewin which take on a fresh water state of 

 existence, more especially as the British Museum possesses some of these so-called 

 hybrids from the Copenhagen Museum. In the series of Welsh fishes the whole 

 of the changes from the anadromous sewin may be explained as natural sequences 

 to ascertained causes and without accepting the theory of their being non-sterile 

 hybrids. 



Much discussion has arisen why some of the salmon breed earlier in certain 

 rivers than in others, whether this is due to the temperature of the water, or 

 occasioned by alterations in the physical conditions of the bed of the stream and 

 its affluents ; or, lastly, to the local breed being an early or late one. This last 

 question involves the consideration of whether necessity having compelled the 

 change from what was an early breeding river into a late one, the descendants of 

 the fish removed to suitable localities would still adhere to the late period of 

 spawning of their immediate progenitors, or return to the earlier time of their 

 ancestral stock. 



In looking at these questions it will be necessary first to consider whether any 

 general rules as to dates of spawning among this family of fishes can be deduced 

 from what occurs in different localities. The period in Great Britain among the 

 salmon may be roughly estimated (excluding local exceptions and climatic 

 eccentricities) at from the commencement of September until the middle of 

 January. 



Sir Humphrey Davy, writing from Southern Austria, remarked that " the 

 charr I got this morning with mature eggs was just about to spawn, yet in England 



* If, as asserted, these are hybrids between two species, the sewin and the brook trout, it is 

 difficult to understand why these is a regular gradation between the two forms. 



