HOLDING FISH 



placed well above the surface of the 

 water. One overflow outlet should be at 

 or near the bottom to remove stagnant 

 water and waste material. 



6. Well water containing more 'than 

 1 p.p.m. of iron will cause heavy minnow 

 mortality. Iron can be removed from 

 the water with the right kind of filter. 

 Some water-softening filters will remove 

 iron if the water is aerated before it 

 is filtered. 



Copper well points and copper water 

 pipes often give off enough copper to 

 kill minnows in holding tanks. This is 

 especially true in soft water or where 

 the pH is high. In such cases, the of- 

 fending pipes must be replaced with iron 

 pipes. 



7. Each tank should be small enough 

 that the complete contents can be sold 

 in a few days. No more fish should be 

 added until these are sold, and the tank 

 should never be overloaded. The trans- 

 fer of fish from one tank to another will 

 greatly aid the spread of disease. 



8. When the fish from one tank have 

 been sold, the tank should be drained 

 and carefully cleaned. The sides and 

 bottom .should be thoroughly scrubbed 

 with a 1 : 10,000 solution of sodium hypo- 

 chlorite. This solution is mixed by add- 

 ing 1 quart of sodium hypochlorite or 3 

 to 5 quarts of any commercial bleach to 

 250 gallons of water. The tank should 

 be thoroughly sterilized at least once 

 a week. After an ample rinse the tank 

 can be filled with water and stocked with 

 fish. 



9. All dead fish in the tanks should be 

 removed immediately and destroyed. 



10. There may be considerable loss 

 from the common practice of selling 

 minnows wholesale by the gallon. This 

 procedure necessitates the measuring of 

 minnows in a nearly dry state. Such 

 measuring cannot be done without injury 

 to the fish. 



11. Very large dip nets should not be 

 used for minnows. Lifting a half bushel 

 of minnows in a dip net is likely to injure 

 those on the bottom. Overloading 



smaller nets will also produce injury and 

 consequent loss of fish. 



12. Feed minnows that are held for 

 more than a few days. A series of feed- 

 ing experiments conducted by the Wis- 

 consin Fi.sh Management Division to de- 

 termine the effect of food on the loss 

 of minnows in holding tanks, showed that 

 brassy minnows could be held for 63 days 

 at 46° F. with very little loss of weight 

 when fed all the canned carp they could 

 clean up. Fish that received half as 

 much carp survived nearly as well and 

 showed only slightly more loss of weight. 

 Fish that received no food succumbed to 

 heavy infestations of fungus, but those 

 receiving food had very little fungus. 



Minnows will eat a variety of foods, 

 but the most practical foods are those 

 that are easy to handle and ccmvenient 

 to store. The food should appeal to the 

 fish so that it is consumed fast enough 

 to prevent undue contamination of the 

 tank water. Oatmeal and cottonseed 

 meal are satisfactory foods. Meal worms, 

 ftour-weevil larvae, and similar worms 

 are very attractive to minnows and form 

 a substantial food ; but all must be raised 

 for the purpo.se, As this takes quite a 

 bit of time and space, most bait dealers 

 do not use these organisms. Dry dog 

 foods or commercial fish foods can be 

 used as a balanced diet that is easy to 

 handle and is reasonable in cost. 



13. Early treatment of diseased fish is 

 important. Epidemics of fungus disease 

 will produce a large loss of fish in hold- 

 ing tanks. While careful seining, trans- 

 portation, and holding of the minnows 

 will greatly reduce the chances of an 

 epidemic starting, it may happen even 

 in the best-regidated establishments. 



At the start of the epidemic all dead 

 fish should be removed and destroyed 

 at once. The remaining fish should be 

 dipped in malachite green 1 : 15,000 solu- 

 tion (Ys ounce in 15 gallons of water) 

 for 10 seconds. The tank must be 

 drained and sterilized with sodium hypo- 

 chlorite 1 : 10,000 solution. All tools and 

 dippers must be sterilized in the same 



43 



