168 American Fisheries Society 



"FILTROS" 



Experiments are being made with "filtros," a rock-like 

 substance which may be purchased in cylinders %-inch in 

 diameter and 6I/4, inches long. This material is quite 

 porous and while it disintegrates in the course of time, it 

 lasts about four times as long as wood when used for liber- 

 ating air. "Filtros" does not contract when not in use and 

 therefore requires little attention in the way of adjustment 

 However, the experiments with filtros have not been car- 

 ried far enough to warrant its general use on fish distribu- 

 tion cars. 



JET AERATOR 



During the spring and summer of this year a new aerat- 

 ing device which circulates the water in the container and 

 operates by air was used to a limited extent on the distri- 

 bution cars with very satisfactory results. This aerator was 

 devised for the purpose of aerating the water and removing 

 the carbon dioxide gas given off by the fish. 



The device consists of a tube placed on the inside of a 

 larger tube, care being taken to allow room enough to per- 

 mit the water to be forced up in the space between the two 

 tubes. 



There has always been a question in regard to whether 

 the liberation of free air in water is the best method of 

 aeration. It has been noticeable for a number of years 

 that when air circulation is discontinued the fish show signs 

 of distress in ten or fifteen minutes while, if the water is 

 thoroughly aerated by dipping or pouring, they may be left 

 without aeration for as long a time as one hour. The jet 

 aerator, by throwing the water into the air, furnishes a 

 more natural aeration. 



The following extract taken from the log of Car No. 8 

 is typical of reports received from those who have tried the 

 jet aerator: 



"These aerators showed their superiority over the ordinary wooden 

 plug when a number of fingerling sunfish were moved from La Crosse, 

 Wisconsin, to Denver, Colorado, in July of this year. When received on 

 the car, these fish had just come out of hot sloughs along the upper 

 Mississippi River and were very weak. There was a rather heavy 

 loss but the pails having the jet-pump aerators in them had consider- 

 ably less loss than the other pails with wooden aluminum plugs." 



Experiments with this device are still being carried on 

 and while its practicability is not generally perceived at 



