1 132 BULLETIN OF THE BUREAU OF FISHERIES. 



ridge at the same time lengthens, it becomes filled with eggs. The position of 

 these eggs is shown in figure 3, page 1 1 26, by the black dots among the stones of 

 the gravel ridge. The eggs are undoubtedly fertilized at the moment they are 

 laid, but owing to the fact that the seminal fluid of the male is colorless its 

 emission can not be observed. 



Security 0} nest structure. — The structure of the nest (fig. 3, p. 1 126) is such as 

 to afford the eggs protection, for, as already pointed out, the base of it is composed 

 chiefly of larger stones, which the male drops directly on the end of the ridge, 

 so that they roll down toward its bottom. Among these larger stones the eggs 

 are lodged. The surface of the ridge is, on the other hand, composed chiefly 

 of smaller pebbles which there fill the chinks between the larger stones. By 

 this arrangement the eggs in the spaces between the larger stones in the base 

 of the ridge arc separated from the free. water above by the fine gravel which 

 closes these spaces at the top and are thus protected. 



When the nest of the horned dace has been completed it is a conspicuous 

 object on the bottom of the stream, because the pebbles that compose it are 

 clean and stand out in sharp contrast to the ooze-covered pebbles of the sur- 

 rounding bottom. But within a very few days the sediment from the stream 

 covers the nest pebbles also and the nest becomes then almost indistinguishable. 

 Meantime the builder of the nest, now that his breeding ardor has run its course, 

 has abandoned his work, and the nest with its contained eggs is left to its fate. 

 Here the eggs undergo their development, and after a time, which varies with 

 the temperature of the water, the young fish hatch from them. The eggs or 

 the newly hatched fish may be obtained at any time by scooping up a part of the 

 nest gravel and agitating it with water, when the eggs, which float for a moment 

 in the agitated water, may be poured off. The newly hatched dace do not 

 differ greatly in their general features from the adult, but no accurate description 

 of them has been made. How long they remain in the nest is not known, nor 

 has their method of exit from it been observed. They must soon make their 

 way out through the spaces between the pebbles and through the overlying 

 ooze, but the precise time and method of accomplishing this are not known. 

 Very small dace and those of every intervening size up to the adult are found 

 in the same streams with the parent fish and differ from them apparently only 

 in the smaller size of the prey which they capture and in occupying a slightly 

 different habitat. 



The nest of the dace affords an absolute protection of its eggs and young 

 against the smaller carnivorous fishes, and this protection arises from two sources. 

 The presence of the male dace on the nest keeps these little enemies at bay while 

 the eggs are being laid and while they are being covered by pebbles. This protec- 

 tion extends over some days at least. Besides this the covering of stones over 

 the eggs effectually excludes small fish after the male dace has left the nest. 



