338 



BULLETIN OF THE UNITED STATES FISH COMMISSION. 



The problems of aeration seem closely connected with those of fungous growth, as 

 may be seen in the following paragraphs: 



Inroads of fish fungus, Achlya. — The greatest difficulty encountered by Prof. Ryder 

 in his experiments at Delaware City appeared to be due to fungous growth. This would 

 be found to arise at various points of the hatching-tray during the first 48 hours of 

 hatching, and would gradually spread its velv T ety encasing over and stifle the entire] 

 egg mass. For success in hatching, water sterilization was then suggested, the fungous 

 spores to be removed by use of either filters or heat. 



The effect upon fungous growth of more perfect aeration and increased salinity ofj 

 water, however, had not been positively determined. And in the following experi-J 

 ment the writer aimed to reconsider these matters, hoping that favorable results 

 might suggest a simpler and less costly means of evadiug fungous growth. 



The results of Prof. Ryder had been obtained in a small fresh-water pond empty- 

 ing through the river bank directly into the Delaware; the hatching-cases had beei 

 placed in a sluiceway through which water was constantly escaping; yet in spite of 

 this current, fungous inroads had here destroyed all but a few of the fertilized eggs.' 

 It was the plan of the writer to array a line of hatching-cases from this shore point 

 near the mark of low water out as far as the edge of the channel in deep water. Byj 

 this means (the cases to contain eggs in every way similarly conditioned) the effects 

 of differences of salinity, aeration, and silt deposit upon fungous growth seemed most 

 likely to be understood. Surface waters of mid stream, stronger in current, would 

 naturally be better aerated and more devoid of silt than marginal waters. In channel, 

 moreover, the water density was noted at 1.007 (sp. gr.). 



The success of the experiment seems clearly to indicate the means that may he 

 here taken to obtain practical results. The eggs in strong current, in Salter and less 

 silty waters were practically exempt from attacks of fungus; those in marginal waters 

 speedily perished (see table). It would in fact seem to the writer that the fungus is 

 rather a consequent than a prime cause of egg destruction. That it is lacking under 

 the natural conditions of sturgeon hatching is a fact not the most remarkable, and 

 that it may be obviated in artificial processes by imitation of the natural hatching 

 conditions seems the simplest plan of cultural procedure. 



No. of 

 case. 



II 

 III 

 IV 



V 



Location. 



At outlet of fresh pond, as in experiments of Prof. 



Ryder 



At stake near line of low water 



At wharf sluice a rod farther out 



At wharf end a rod farther out 



In deep water in current at breakwater 



Percentage of eggs destroyed by fungus. 



Second 

 day. 



100 

 60 

 20 



Third 

 day. 



100 



80 



20 



5 



Fourth 

 day. 



100 



50 



5 



Fifth 

 day. 



60 

 5 



In. the above results the problem of hatching sturgeon eggs is doubtless intimately 

 conditioned by water current, by silt deposits, by salinity of water. To determine to 

 what degree each of these factors is contributive to success would doubtless be very 

 difficult. In the ease of the common anadromons sturgeon (Acipenser sturio) a slight 

 degree of brackishness of water might be regarded as a favorable, if not a necessary 

 condition, were it not that the eggs of this species have been repeatedly hatched in 





