544 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [6] 



pose; but the process of filtering should be repeated near the fish cult- 

 ural establishment. 



Mr. Haack justifies the absence of filtering apparatus by saying that 

 practice has shown the sediment to be harmless, and I can state from 

 personal observation that fish eggs have been successfully hatched at 

 Hiiningcn even in hatching-boxes and in California apparatus, supplied 

 with water directly from ditches without any grating at the entrance. 



At Max von dem Borne's establishment I saw in operation the filter 

 with several chambers, terminating with the so-called American filter 

 (of flannel), but in answer to my inquiries he stated that for filtration 

 there might be substituted the washing of the eggs by letting water fall 

 on them from a certain height from the pierced spout of a simple water- 

 ing-can. This proves at any rate that this eminent fish-culturist has 

 not abandoned the idea above referred to, that the sediment is hurtful, 

 as long as he tries to remove it in some way or other. 



Those who maintain that filtration is useless can not say that they 

 follow the example of nature, because if it is true that the trout cover 

 the eggs which they lay in brooks, they do it with small stones and not 

 with mud; and the sediment cannot adhere to the eggs, because they 

 are continually kept floating by little currents passing through the 

 crevices between these stones. 



I am not able to explain the difference of opinion in this respect among 

 such competent persons ; but I have no doubt that in every case the 

 opinion is based on experience drawn from the peculiar practice pre- 

 vailing in the different localities. It is generally agreed that if the 

 quantity of the sediment exceeds certain limits it becomes hurtful to 

 the eggs, preventing free respiration. But as regards allowing a small 

 quantity of sediment, people should be guided by its quality, which in 

 one place may be such as to render its removal necessary, while in 

 others it may be left without running any risk. 



Of whatever description the filtering apparatus may be, the filtering 

 should be done through thick or relatively indestructible matter, sand, 

 or fine gravel, alternating with layers of charcoal, sponges, &c. Even 

 then it may not be entirely efficacious in directly preventing the devel- 

 opment of the minute spores, which are among the most dangerous en- 

 emies of pisciculture. But if sediments of a mineral nature are com- 

 bined with organic matter, which may sometimes happen (although the 

 combination may greatly vary in its character), I think a mechanical 

 process of filtration may indirectly be successful by keeping the para- 

 sites away, or at least diminish their spreading, since only organic mat- 

 ter contains the conditions favorable to their growth. There is no 

 doubt, however, that the antiseptic property of coal, which is largely 

 employed as a means of filtration, is lost after a short time, so that after 

 a certain time the filters will only act in a mechanical way. For this 

 reason I would like to know whether any experiments have been made 

 in pisciculture with filtration by "carferal" (carferal, or iron sponge,, 



