STUDYING THE HABITS OF FISHES. II 33 



At the same time the top covering of small stones filters out much of the sedi- 

 ment which would otherwise sift down upon the eggs and smother them or 

 carry to them the fatal spores of fungus. 



The horned dace and the other minnows that build stone nests are rela- 

 tively small fish, toothless, and without spiny fin rays, so that they have no 

 effective means of repelling the attacks of their enemies. They would therefore 

 be unable to protect their eggs by guarding them in open nests after the manner 

 of the larger and more formidable fresh-water dogfish and black bass. By 

 building stone nests which inclose and protect their eggs, certain of these 

 minnows, including the horned dace, seem to have followed the most effective 

 method open to fish which are physically incapable of personally defending 

 their offspring. 



Destructive agencies. — Yet the nests of the horned dace are not impreg- 

 nable castles. Against the smaller carnivorous fishes they afford ample pro- 

 tection, for the stones of which they are built are too heavy to be moved by 

 Rhinichthys, Pimephales, Etheostoma, and the like. On the other hand, the 

 nests may easily be disturbed and even robbed by larger fishes. Campostoma 

 and Catostomus habitually uproot small stones in the process of feeding, and it 

 is possible that in this way they uncover and devour the eggs of the horned 

 dace, though I have not observed this. But there is another way in which the 

 structures built by the horned dace are frequently torn to pieces and their con- 

 tained eggs probably devoured, and that is by the nest-building operations of 

 other fish. When a horned dace nest has been completed by its builder and 

 abandoned, a second dace frequently selects the same site for his nest and 

 proceeds to build with the materials used by his predecessor. Or a Campos- 

 toma may use the gravel ridge of a horned dace nest as a suitable place in which 

 to excavate his pit, or a Hybopsis may carry away some of the dace materials 

 in building his nest. These fish all build at about the same time, and their 

 pits, ridges, and stone piles occur on the same areas. By this process of the 

 repeated occupation of the same area by other fish of the same and other species, 

 the nests of the horned dace are often disturbed, and in such cases the contained 

 eggs are probably in part destroyed. The extent to which this happens varies 

 in different streams. In certain streams areas which I have kept under obser- 

 vation have been utilized as nesting sites two or three times in succession, and 

 the first dace nests built in them have been thereby wholly or in part 

 destroyed. In other streams most of the dace nests have been left undisturbed. 

 Again the top dressing of fine gravel by no means suffices to exclude all 

 sediment. Sediment and fungus spores reach the eggs. In many of the 

 nests that I have examined, living eggs were found in the new-built parts, 

 while the older parts contained only dead eggs matted together and covered 

 by fungus. 



