CHAPTER LI 



THE ORDER OF HALF-GILLED FISHES 



HEMIBRANCIIJT 



Because of the fact that a few very small 

 fishes have less than their rightful number of 

 gill-arches, and shoulder-girdles with one bone 

 only instead of two, the Order of Half-Gilled 

 Fishes has been created. 



The Sticklebacks are very small fishes, only 

 a few inches in length, and derive their name 

 from the formidable dorsal spines that stand 

 upon the back in front of the dorsal fin. We 

 have Two-Spined, Four-Spined and Ten-Spined 



observers say that the fish first brings a few 

 stems and bits of vegetation, and by means of 

 his gelatinous secretion practically ties them 

 fast to the upright stalks, to use as a foundation. 

 The fish then proceeds to exude its secretion 

 and dispose it in commingling rings, vertically, 

 around a space sufficiently large for the female 

 Stickleback to pass through. In a manner noth- 

 ing short of marvellous, a hood-like nest is spun, 

 of the fish's own secretion, which well retains its 



Drawn by J. Cakter Beard. 



TWO-SPINED STICKLEBACK. 



Sticklebacks, all three being found in brackish 

 water along the Atlantic coast from Cape Ann 

 to New Jersey. 



All the Sticklebacks are celebrated for their 

 nest-building habits. The abdomen of the male 

 fish has been provided with a large gland which 

 is "filled with a clear secretion which coagulates 

 into threads" when it comes in contact with 

 water. At first the fluid is colorless, but after 

 contact with water it becomes whitish, and its 

 many fibres hang together like strings of spa- 

 ghetti. (Ryder.) 



The entire work of nest-building is performed 

 by the male Stickleback. It begins by selecting 

 a bottom situation, in a gentle current, wherein 

 the nest can be attached to two or more stems of 

 growing vegetation, and anchored fast. Some 



shape for some weeks. In this the female de- 

 posits her eggs, all the time jealously watched 

 by the male, to prevent her from eating them! 

 The male guards the eggs until they are hatched, 

 and it is said that if the current flowing through 

 the nest does not meet his views as to strength, 

 the fish increases the volume of it by moving its 

 pectoral fins to and fro. Sticklebacks are some- 

 times kept in aquaria in order that they may 

 show their wonderful intelligence in nest-building. 

 The Two-Spined Stickleback 1 will serve 

 as a type for the whole Order. It is only about 7 

 inches long, and has no commercial value. It 

 is said to occur in quiet brackish waters along 

 our coast, but is seldom brought into notice out- 

 side of aquaria. 



1 Gas-ter-os'te-us a-cu-le-a'tus. 



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