26 KlSll HATCHERY MANAGEMKNT 



lies in the greatly reduced volume of effluent to be treated compared with 

 single-pass hatcheries. 



HATCHERY POLLUTANTS 



Generally, three types of pollutants are discharged from hatcheries: (l) 

 pathogenic bacteria and parasites; (2) chemicals and drugs used for disease 

 control; (3) metabolic products (ammonia, feces) and waste food. Pollution 

 by the first two categories is sporatic but nonetheless important. If it 

 occurs, water must be sterilized of pathogens, disinfected of parasites, and 

 detoxified of chemicals. Effluent water can be sterilized in ways outlined 

 for source water (page 17). Drug and chemical detoxification should follow 

 manufacturers' instructions or the advice of qualified chemists and patholo- 

 gists. Standby detoxification procedures should be in place before the drug 

 or chemical is used. 



The third category of pollutants — waste products from fish and food — is 

 a constant feature of hatchery operation, and usually requires permanent 

 facilities to deal with it. Two components — dissolved and suspended 

 solids — need consideration. 



Dissolved pollutants predominantly are ammonia, nitrate, phosphate, and 

 organic matter. Ammonia in the molecular form is toxic, as already noted. 

 Nitrate, phosphate, and organic matter contribute to eutrophication of 

 receiving waters. For the trout and salmon operations that have been stud- 

 ied, each pound of dry pelleted food eaten by fish yields 0.032 pound of 

 total ammonia, 0.087 pound of nitrate, and 0.005 pound of phosphate to 

 the effluent (dissolved organic matter was not determined separately). The 

 feed also contributes to Biological Oxygen Demand (BOD), commonly 

 used as an index of pollution; it is the weight of dissolved oxygen taken up 

 by organic matter in the water. 



More serious are the suspended solids. These can, as they settle out, 

 completely coat the bottom of receiving streams. Predominantly organic, 

 they also reduce the oxygen contents of receiving waters either through 

 their direct oxidation or through respiration of the large microbial popula- 

 tions that use them as culture media. For the trout and salmon hatcheries 

 mentioned above, each pound of dry feed results in 0.3 pound of settleable 

 solids — that part of the total suspended solids that settle out of the water 

 in one hour. Most of these materials have to be removed from the effluent 

 before it is finally discharged. Typically, this is accomplished with settling 

 basins of some type. 



It should be noted that except for ammonia, the pollutants listed can be 

 augmented from other sources such as waste food and organic material in 

 the incoming water. The fish culturist should not assume that the total pol- 

 lutant concentrations in the effluent are derived only from food eaten by 

 the fish. 



