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SOME EXPERIMENTS ON COLOUR-CHANGE IN 

 THE TENCH. 



By H. N. Milligan, F.Z.S. 



It is well known that the colour of the Common Tench 

 (Tinea vulgaris) adapts itself to the surroundings in which the 

 animal lives,* but a short account of seven experiments on 

 colour-changes in this fish may perhaps be of interest. The 

 first two experiments were involuntary ones. 



1. Two healthy female Tench, each of about six inches in 

 length, had been living in an aquarium, the floor of which was 

 covered with dark brown pebbles and the back with dark brown 

 rocks. The fishes were of a dark bronze-green colour, with their 

 fins tinged with green and their irises of a deep coppery red; 

 and this colouration had not varied, so far as I could see, or at 

 all events had varied little, during the whole of the time (more 

 than two months) they had been in the aquarium. At 11 a.m. 

 on February 26th, however, they were removed to a second 

 aquarium, which was in a somewhat lighter place opposite to a 

 window, containing whitish pebbles and with a back of newly- 

 made rockwork in great part composed of white cement, against 

 which the dark green bodies of the fishes stood out conspicuously. 

 At 9.30 a.m. on the next day my attention was drawn by another 

 person to the fact that the fishes had undergone a striking 

 change of colour. Their bodies were now of a pale yellowish 

 colour, with only a very faint tinge of green, which gave them a 

 sickly appearance, their fins being almost colourless and their 

 irises orange. The change had certainly brought their colour 

 more into harmony with the general colour of their background 

 of pebble and rockwork. The aquarium was a comparatively 

 small one, measuring two and a half feet in length and one and 

 a half feet from back to front, and the two fishes could therefore 



* See, for example, ' A History of Scandinavian Fishes,' Part 2, p. 750, of 

 Fries, Erkstrom & Sundevall, second edition of Smitt. 



Zool. 4th ser, vol, XIX., September, 1915. 2 D 



