PARENTAL CARE AMONG FRESH-WATER FISHES. 458 



The color is uniforiu blackish above and silvery on the sides. It 

 reaches a size of about 18 inches. Its nesting peculiarities have been 

 described by Richard Semon in his work entitled " In the Australian 

 Bush" (1899, p. 19G). 



The bolla was found by Semon to resort to " flat, sandy, and stony 

 parts " of the river, '' under a rapidly passing current," to spawn. In 

 such places, in August — that is, in early spring in northern Austra- 

 lia — Semon " found numerous light-colored circles of about a yard 

 across." On looking more closely he " often noticed a fish ; wimming 

 about inside this ring, and, as it seemed, occupied with a work of im- 

 portance. On examining the ring itself, which has a breadth of about 

 eight inches," he found that its light color was " due to the removal of 

 all stones, large and small, from its surface. They had been carefully 

 carried into the inner circle, so that the surrounding ring shoAvs the 

 gleaming white sand of the river bed, bare of every pebble. The ring 

 "hows no other peculiarity. The inner circle," however, excited his 

 interest. At the top he found several layers of big stones, among 

 which nothing was to be discovered. These Avere succeeded b}^ a mix- 

 ture of small pebbles and coarse river sand, beneath whicli followed 

 the common river ground. At first Semon was unable to find eggs in 

 any of these layers, though he closely examined them. Observation 

 through the rapidly flowing water was, however, far from easy, and 

 being sure that this was the depository of the eggs, he further investi- 

 gated the matter. He took out a part of the gravel, cleaned it from 

 sand by passing it through a strainer, and thus found numerous small 

 eggs — small in comparison with the eggs of the egg carriers, but large 

 in comparison with those of most fishes. They had a diameter of 

 about one-eighth of an inch, and were surrounded by a " closely fit- 

 ting tegument." 



The manner in which the nest thus observed is made has been 

 explained at length by Semon : 



When depositing its eggs and building its nest, the fish goes to worlc in the 

 following way. It begins by preparing a bedding about half a yard in area, 

 consisting of gravel and small pebbles, among which it deposits the spawn, 

 which is instantly milted by the male. After this it covers up the eggs by sev- 

 eral layers of bigger stones, thereb.y preventing them trom being washed away 

 b.v the stream or being carried off by water-birds fond of this kind of caviare 

 or by marauding little fishes. The material for this defensive structure is derived 

 from the above-mentioned ring, which thereby becomes devoid of all stones and 

 gleams brightly in its smooth garl) of white sand. It is wonderful to observe 

 the accuracy of the fish's handiwor]< and the jierfect cirble described by the 

 ring. So far as I could see, the fish moved the bigger stones by pushing them 

 along with its tail. 



The whole affair shows a very clever arrangement, the eggs thus being well 

 shielded from enemies, well vetitilated by the current and even protected against 

 being mud-stifled (save in case of a downright flood). 



