But, of all the family, the mackerel is the most fitted for 

 rapid propulsion and has the most powerful tail ; and this, 

 you know, means the greatest power of propulsion, for the 

 sole natural propulsive power of every fish lies in its tail. 

 I once proved this beyond question, thus : We stay in 

 summer in a house so close to the sea that we are in our 

 boat within a minute of our leaving our front door, and we 

 have there a pill, or salt water pool, in the rocks, about 

 thirty feet long by ten wide by three deep, which is left by 

 the tide for about six hours in every tide, and into this pool 

 we put the fish which we bring in alive from our trammels 

 every morning, and watch them until we want them. 



I have watched an octopus in that pool many times. But 

 once I cut off the tail of a fish, a pollock I think, and I 

 put it in this pool. At first the fish did not realise its loss, 

 and we saw the stump of its tail working, but the other fins 

 were, as usual, only balancing the fish. There was no 

 progression. After a while the fish stopped working the 

 stump of the tail, and lay simply balanced. About an hour 

 afterwards I came back to it, and it was slowly progressing by 

 using its pectoral fins (those next behind the gills) as oars. 

 I had seen all I wanted to know, and had ascertained that 

 the tail fin was the fin of propulsion, that the fish had sense 

 enough to find out when it had lost it, and reason enough 

 to adapt its pectoral fins to a use for which they were never 

 intended. I then killed the fish, but my conscience did not, 

 nor does it, accuse me of any cruelty towards it. It showed 

 no symptoms of pain. Indeed, of all the very many 

 thousands of fish that I have seen die, I never saw one show 

 symptoms of pain. The nearest approach to it has occurred 

 in the crimping of skate immediately on its being taken out 

 of the water. The crimping is done by drawing a sharp 

 knife in three cuts to the bone, on each side of and parallel 



