108 FISH CULTUEE 



perforations in the bottom. The principle is good, 

 since it allows the water in the bottotn, which is in the 

 poorest condition, to be taken out and aerated. There 

 is no patent on the apparatus and all who will may use 

 it. Another useful device is a tin cylinder about two 

 feet long, three inches in diameter, having a fixed 

 handle at the top and the bottom pointed like a lead 

 pencil. The pointed end is thickly perforated. To 

 aerate with this, plunge the pointed end to the bot- 

 tom, and then withdraw it, allowing the water to run 

 back into the can through the perforations. 



Thermometers are among the useful instru- 

 ments needed, although messengers and men 

 about the hatchery should be taught to guess 

 closely the water-temperature by feeling with 

 the hand. By dint of practice the average 

 hatchery-man can estimate temperature very 

 nearly. 



A meat-grinder, for grinding liver and lungs 

 for fish-food, is indispensable. It must, how- 

 ever, have a number of discs with perforations 

 of varying diameters so as to cut meat of dif- 

 ferent degrees of coarseness. If the hatching 

 establishment is of considerable size it will be 

 almost necessary to operate the grinder by 

 power. This can be done by erecting a small 



