108 



DR. M. c. fish are well fed, and will not be tempted by a bait, but, when water is low, it 

 COOKE. i s a common proverb that fish will be hungry. With an influx of additional 



feeders, such as would be the case when salmon return to the rivers, and this 



taking place at low water, a scarcity of food .would follow, and hence debility. 

 It might even be supposed that gravid fish would be more than ordinarily 

 voracious, which would tend to a diminution of the food supply. Another of 

 the consequences of low water is that the fish congregate in the holes of the 

 stream; and in this overcrowding, which is an inevitable consequence, another 

 source of debility is provided. Overcrowding in holes of this kind is analogous 

 to overstocking an aquarium, the water gets no aeration, its air is exhausted, 

 and the fish must become the prey of disease. On a large scale it is a repetition 

 of the experiment of carp in a tank. Before salmon disease was thought of, it 

 was known that carp and other fish would be attacked by the same fungus if 

 too many were together, or the water was not properly aerated. There is 

 another problematic view in which this collecting of fish in holes is to be 

 regarded. If it is assumed that the resting-spores of the disease, being heavier 

 than water, sink to the bottom, they will consequently be washed into the 

 holes, which would become reservoirs for the zoospores which are liberated in 

 the spring from the oogonia, or resting spores. If this be the fact, and it is 

 plausible, then there is also an excess of fungus spores in the holes waiting to 

 attack any sickly or debilitated fish. When the water is high and plentiful 

 the fish do not collect in the holes, are not debilitated by overcrowding, and 

 are not forced into the midst of contagion ; consequently at such times there is 

 less disease. This is not mere speculation, it is a view which is fully borne 

 out by the evidence. We cannot forget that the fish-fungus is no respecter of 

 species or individuals. It attacks nearly all, if not all, freshwater fish. It 

 exhibited its predeliction for carp before the salmon disease became prevalent. 

 How is it that all the fish in the infected rivers are not destroyed as well as the 

 salmon ? The only answer possible is, that in some condition of bodily health, or 

 physical weakness, the salmon falls a prey, whilst the carp and roach by a more 

 robust constitution, or some peculiar circumstances which the salmon does not 

 enjoy, escape " scot free." If the conditions of all were equal, the consequences 

 also would be equal. Some weight must be attached to the argument which has 

 been advanced, that disturbing the natural conditions, by protecting the salmon, 

 has tended to the production of a weaker and physically degenerated race. We 

 cannot deny that artificial arrangements for the control of nature inevitably fail. 

 We make war upon small birds, and then exhibit surprise that the insects make 

 war upon us, or upon our fields and orchards. We destroy all the destroyers 

 of sickly salmon and then express surprise that we rear a sickly race. The 

 argument was placed in a strong light when compared with the grouse disease. 

 One writer says, " Take the case of the red grouse on our moors. The birds 

 " are protected by law for the greater part of the year, and their natural enemies, 

 " the various raptorial birds, are so assiduously hunted down as to have 

 " become in some cases practically extinct in this country ; and the consequence 

 " of this destruction of their natural enemies has been that all the weakly 

 " birds, which in natural circumstances would have been picked off by 

 " the larger hawks have remained to breed and perpetuate a still weaker 

 " progeny. In a race of birds thus weakened the parasite found everything to 

 " favour its propagation, and the grouse disease became an epidemic; and 

 " many proprietors recognising this are now protecting the peregrine falcons 

 " as strictly as they preserve the grouse. Something very similar has taken 

 " place with the salmon. The otter is the natural enemy of the salmon in the 

 " fresh waters, but they have been hunted, trapped, and shot, till not one 

 " remains, where formerly there were dozens. The otter, like the peregrine, 

 " takes the prey most easily captured, thus removing the weakly, the sick, all 

 " those which, from whatever cause, would cause a degeneration of the breed. 

 " If there had been otters in the district in the numbers in which they once 

 " were, those wretched looking salmon to be seen along the sides of the Nith 

 " would all have been dragged out and eaten by them. I am confident the 

 " disease would be checked if the otters, just for a change, were protected for 

 " a year or two. The course of the salmon disease and the grouse disease tells 

 " us in unmistakable language ,to beware of altering the balance of nature. 

 " Left to herself the great law of the ; survival of the fittest ' would always 



