14 MARVELS OF FISH LIFE 



the three-spined stickleback. During most of the year 

 the male and female fish are coloured alike, being olive- 

 green and grey on a silvery background, but about April 

 the male fish, in order to attract the opposite sex, becomes 

 brilliant in colour. At first there is a mere reddish 

 tinge on the under-surface, but as the time approaches 

 for him to build his nest his sides and under-surface, 

 and even the inside of his mouth, become scarlet, his 

 back turns a greenish blue, and his little eyes become a 

 brilliant emerald. When he decides to build he first 

 scoops out a hollow in the ground, and then arranges 

 round this hollow small pieces of roots, weed-stems, 

 and other debris, either tugged from the growing vege- 

 tation or picked up from the bottom. Wriggling 

 through this untidy mass, he binds the pieces together 

 with the mucus from his body. 



Next he nips off bits of the same roots and stems, 

 and, after chewing them well in his mouth, rams them 

 into the bottom of the nest. Having put in three or 

 four mouth fuls of material in this manner, he will 

 suddenly dart off into the adjacent weeds, talk for a few 

 seconds to his intended bride, and then return brighter 

 in colour to tackle his work with renewed energy. These 

 periodic visits stimulate the secretion with which he 

 welds together the building material. Finally the end 

 and roof of the nest are completed, and it appears as 

 a mound on the ground, surrounded by general debris. 

 Working from early dawn to dark without intermission, 

 the stickleback completes his task in a couple of days. 



