hatchery requirements 27 



Table 3. pollutant levels in the effluent frcjm earthen catfish rearing 

 ponds during fish seining and draining of the pond. (after boyd li»79.) 



I'ONI) USH 



POLLLTANl'' ORAIMNG SF.INING 



Settleable solids (ppm) O.OH 28. .1 



Settleable oxygen demand (ppm) 4.31 28. i) 



Chemical oxygen demand (ppm) 30.2 342 



Soluble orthophosphate (ppb as P) Hi .'J9 



Total phosphorus (ppm as P) 0.11 0.49 



Total ammonia (ppm as N) 0.98 2.34 



Nitrate (ppm as N) O.Hi 0.14 



Concentrations (parts per million or per billion) are on a weight basis except for settleable 

 solids, which are on a volume basis. 



The levels of pollutant in a hatchery effluent can be determined with the 

 following general equation: 



,, pollutant factor X lbs food fed 



Average ppm pollutant = -. ^ 



water flow Igpmj 



The following pollutant factors should be used in the equation: 



Example: A trout hatchery in which fish are fed 450 pounds of food per 

 day and which has a water flow of 1,500 gallons per minute has a total 

 ammonia concentration of 0.8 parts per million in the hatchery effluent. 



. 2.67 X 450 



ppm ammonia = -: = O.o 



^^ 1500 



Studies in warmwater fish culture have shown that there is no consistent 

 relationship between the weight of fish harvested in earthen ponds and the 

 amount of settleable solids discharged in the effluent. In general, an 

 increase in fish weight results in an increase in settleable solids. Pollutant 

 levels in the discharge from earthen ponds vary with the volume of water 

 being discharged and the pond design. Some pollutant levels that have 

 been reported in the effluent of catfish ponds are presented in Table 3. 



SEDIMENTATION BASINS 



The principle of sedimentation basins is to spread flowing hatchery effluent 

 out in area, thus slowing it down, so that suspended solids will settle out of 



