228 "PERFECT-MOUTHED" FISHES 



a continuous current of fresh, well - oxygenated water to pass 

 through it." 



The stickleback is not very difficult to keep, and forms a most 

 interesting addition to the fresh-water aquarium, where we have 

 an opportunity of watching its habits at our leisure. 



The larger Fifteen-spined Stickleback (Spinachia vulgaris), a 

 marine species, is just as devoted a parent. It makes its nest in 

 sheltered bays, harbours, or sometimes in the rock pools round 

 our coast. The material chosen is usually a tuft of growing sea- 

 weed, or a bunch of hydrozoa, and the fish binds the fronds or 

 branches closely together with a silken thread which he spins 

 from his own body, and is said to be secreted by the kidneys of 

 the male solely during the breeding season. As he spins his thread 

 the stickleback swims round and round the clump of weed and 

 thus forms a species of cocoon, somewhat after the manner of a 

 spider. Over this, when he has induced a female to deposit her 

 spawn inside it, he keeps constant watch and ward until the young 

 fry emerge. The Fifteen-spined Stickleback is apparently the 

 only vertebrate capable of spinning threads in this way. 



The nest-building habit is, with one exception (so far as we 

 know), confined to certain fresh- water fishes and marine species 

 frequenting shallow waters. The exception is the work of a fish 

 whose identity has not been established, but is believed to be 

 one of the Flying-fishes. The nest in question is found floating in 

 mid-ocean in the midst of the masses of Sargasso weed in the North 

 Atlantic. It is almost round in shape, about 6 inches in diameter, 

 and is made of fronds of weed bound together by threads, which 

 are not, however, spun by the parent fish, but are bundles of 

 filaments proceeding from the opposite poles of the eggs within 

 the nest. 



The little Sand Goby (Gobius minutus) is one of the nest-building 

 fishes. The male fish seeks a large, empty shell, usually a pecten 

 shell, lying in an inverted position in shallow water, and indus- 

 triously scoops away the sand from beneath it, thus excavating a 

 neat little chamber with the shell forming the roof, as it were. 

 In this nest the female Goby deposits her eggs, which are of an 

 adhesive nature, fastening them to the under-surface of the shell 

 roof. The male fish remains on guard to protect the eggs and 

 keep them supplied with a sufficiency of oxygen by the vigorous 



