82 MARVELS OF FISH LIFE 



Changes in colour and markings are generally attri- 

 buted to environment. A trout, for example, living in 

 a deep hole of a brook, with a muddy bottom, is found 

 to lose his bright spots, and to become of a dull colour, 

 whereas the same fish living in a rapidly flowing stream 

 with a gravelly bottom becomes bright in colour, and 

 covered with numerous well-marked spots. 



Though environment undoubtedly has a material 

 effect upon the coloration of the trout, food is an equally 

 important factor in bringing about colour changes, and 

 both colour changes and silvery iridescence may result 

 from food and food alone. 



As an illustration of this point, I would quote from 

 the experience of my friend, Mr. Richmond. 



On his fish farm at Shottermill are two similar ponds 

 about one hundred and twenty yards apart. These 

 were supplied from the same water source, but the food 

 in them was of a totally different character. The upper 

 pond abounded in molluscse, but the food in the lower 

 pond consisted almost entirely of daphnia and cyclops. 

 Both these ponds were stocked at the same time -with 

 trout similar in appearance. Very soon, however, the 

 fish in the upper pond became dark in colour with in- 

 tense red spots and yellow underparts, while those in 

 the lower pond assumed a silvery appearance shot with 

 a pale pink hue. 



The silvery appearance of the trout in the second 

 pond, was due to deposits of light-reflecting spicules, 

 known as iridocytes on the scales of the fish. When 



