HATCHERY OPERATIONS 101 



The form of calcium to apply depends upon the primary purpose for 

 which it is used. Unless bottom mud is below pH 7, lime is not recom- 

 mended except for sterilization purposes. For general liming, calcium hy- 

 droxide or ground limestone are the forms most suitable. Each has certain 

 advantages and disadvantages which make it desirable in specific situa- 

 tions. 



Waters softer than 10 parts per million total hardness generally require 

 applications of lime, whereas waters harder than 20 parts per million sel- 

 dom respond to liming. The need for lime may be indicated when inor- 

 ganic fertilization fails to produce a substantial plankton bloom. However, 

 analysis of the water or, preferably, of the bottom mud should be made for 

 total hardness and alkalinity before lime is applied. A state agricultural 

 experiment station or extension service can assist with these (and other) 

 analyses. 



Liming can be done with the pond either dry or filled with water. Suit- 

 able mechanical equipment is needed to assure uniform dispersion. A 

 boat- mounted spreader can be used for ponds filled with water. If the pond 

 contains water, additional amounts of lime may be added to satisfy the 

 needs of the water as well as of the bottom mud. It may take 3 to 6 months 

 before the pond responds. In some situations, limed ponds revert to an acid 

 condition within two years after the initial application. 



COMBINING FERTILIZERS 



In making a decision on whether to use organic or inorganic fertilizers, the 

 advantages and disadvantages should be carefully considered. Comparative 

 tests have been attempted but conclusive answers as to which material is 

 best often will depend upon the individual situation or production cycle in- 

 volved. 



Combining organic and inorganic fertilizers is a common practice. Many 

 workers have found that a combination of an organic meal and superphos- 

 phate, in a ratio of 3:1, gave higher fish production than the organic 

 material alone. In hatchery rearing ponds where draining is frequent and 

 time for development of a suitable food supply often is limited, combining 

 organic and inorganic fertilizers appears to be advantageous. While the 

 cost of such a procedure is greater than with inorganic fertilization, the 

 high value of the fish crop involved normally justifies the added cost, 

 particu- larly in the case of bass and catfish rearing. 



The ratio of 4-4-1, N2-P20-,-K20, is needed to produce favorable 

 plankton growth for fish production ponds. The fertilizer grade most com- 

 monly used is 20-20-5, which gives the 4-4-1 ratio with relatively little 

 filler. 



The type of fertilizer program chosen will be determined by such factors 

 as species of fish reared, time of year, cost, availability of product, and past 



