OPERATING THE HATCHERY 



TRANSPORTING AND HOLDING 

 BAIT FISH 



Aeration and temperature control 

 are important factors in the success- 

 ful operation of both carrying and 

 holding tanks. A series of experi- 

 ments was run in Minnesota to de- 

 termine the effect of these factors 

 on the mortality of fish. It was 

 shown that fathead minnows ex- 

 posed over a period of hours to non- 

 aerated Avaters die with increasing 

 rapidity at the higher temperatures. 

 The most rapid loss occurs at tem- 

 peratures above 65° F. Fathead 

 minnows can be kept in well-aer- 

 ated water for several hours at rela- 

 tively high temperatures without 

 loss, and greater numbers of min- 

 nows can be carried at all tempera- 

 tures in aerated water than in non- 

 aerated water. 



These experiments showed that 

 safe operation of minnow tanks re- 

 quires close adherence to the follow- 

 ing limits : 



1. When tanks are aerated by circu- 

 lating water, a continuous flow of not 

 less than 1 gallon per minute for each 

 25 gallons of water in the tank should be 

 maintained. The water should reach 

 the tank from pressure jets placed so 

 the water is sprayed toward the op- 

 posite side of the tank. Each tank 

 should have a minimum of two pressure 

 Jets and at least one jet for every 25 

 gallons of water in the tank. 



2. When oxygen or other forms of 

 aeration are used, the equipment should 

 be operated so as to maintain a mini- 

 mum of 3 p. p. m. of dissolved oxygen. 

 When oxygen is used for aeration, it 

 should be dispensed into the water 

 through carborundum tips or a per- 

 forated oxygen-release tube. 



3. Water in nonaerated tanks should 

 be kept at 65° F. or lower. 



A popular practice when han- 

 dling minnows is to fill the truck 

 tank at the bait store with cold 

 water (often around 50° F.). 

 While this water is being hauled 

 to the pond, it does not have time 

 to warm up very much. The min- 

 nows are seined from a warm- 

 water pond and placed in the cold 

 water of the tank with only a few 

 minutes of tempering. The shock 

 is not great enough to kill the fish 

 at once, but within a few hours a 

 large percentage will be dead. 

 Those that survive this period 

 usually develop fungus and die 

 within a few days. A minnow 

 should not be subjected to more 

 than a 10° F. change. A pocket 

 thermometer should be used to de- 

 termine temperature differences. 



Likewise, bait fish that are to 

 be used locally should not be held 

 in very cold water unless the fish- 

 erman travels far enough for the 

 water to warm up. Minnows that 

 are taken from a cold minnow pail 

 and put into warm lake water will 

 turn belly up in a few minutes. 



Transporting minnows 



The hauling of minnows over 

 long distances during very hot 

 weather presents a difficult prob- 

 lem. Success depends on close ob- 

 servance of the following impor- 

 tant requirements: 



1. Harden the fish before they are 

 transported. Conditions such as crowd- 

 ing, excessive handling, and changing 

 water temperatures, encountered when 

 transporting minnows for long distances, 



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