CXXVI REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



For the reasons above explained the greatest care must be exercised in 

 taking and handling the spawn. It would be preferable to use filtered 

 water in the hatching work, in order to escape the accumulation of 

 sediment, which settles at the bottom of the jars, and, together Avith 

 dead organic matter, tends to kill the eggs in water of low density. 

 This probably may be obviated, however, by maintaining a higher 

 density than sometimes occurs in this locality, by which means the 

 eggs are kept floating and out of danger. The best results were 

 accomplished and, in fact, nearly all the hatching was done under the 

 latter conditions, which also insure a ready way of separating the good 

 from the bad eggs, sufficiently accurate for all practical purposes. 



In any future experiments it will be advisable to determine if some 

 economical means can not be devised for holding the fry in confinement 

 until they reach a size when they are better able to take care of them- 

 selves. This question has been satisfactorily settled with respect to 

 several other species, and the success which may be attained in the 

 propagation of Spanish mackerel will be measured by the extent to 

 which this feature can be carried out. When the fry are deposited in 

 the open waters of Chesapeake Bay their existence is at once threat- 

 ened by the strong currents and often heavy sediment, and in all 

 places, however much sheltered, they are tlie prey of multitudes of 

 young fishes which swarm in this region. Even though the utmost 

 care was exercised, however, it was found iinjjossible to keep the fry 

 in an aquarium <^)u board the Fish HaicJc for more than one week, but 

 in a iH'operly constructed tidal inclosure better success might possibly 

 be obtained. After the fry began feeding in the aquarium their 

 stomachs were observed to contain a few minute green algse and a 

 mass of material evidently derived through the disintegration of 

 organic substances. The food of the adults during June and July 

 consisted chiefly of young alewives, which were very abundant about 

 the ship, together with various cyprinodonts, silversides, etc. They 

 doubtless devour any small fishes that come in their way. 



Some progress was made in the study of morphology and embryology 

 of this species on board the Fish RawJc, and material was preserved 

 for the purpose of continuing these researches at a later time. 



RIVER POLLUTION. 



In February, 1802, the Fish Commission was requested to investi- 

 gate what was claimed to be a serious case of pollution in the Susque- 

 hanna Eiver near the town of Havre de Grace, Md., having its source 

 in a large mill where j)aper is manufactured from wood pulp. An 

 examination of the conditions existing near the mill was made at once 

 by Prof. Evermann, and careful tests were apjilied to determine the 

 possible effects produced by the outflow of the waste liquor. The 

 results of the inquiry were not conclusive, and, in fact, the studies 

 have not been entirely completed, but, in view of the widespread 



