Fish Hatchery Management - fisheries & aquaculture

HATCHERY REqUIREMENTS 43Tent.n 5. AMMONTA AND oxycEN coNcENTRATToNS tN tDENl'rcAL cTRCULARTANKS WITH HIGH ANI) LOW-PRESSURE WATER SYS'fEMS. TANK DIAME'I'L,RS ARE (JI'EE]', 'I'ANK VOLUMES ARE 530 GALLONS, FLOWS ARE IO GALLONS PER MINUTE(GPM), WATER CHANGES ARI] I.I3 PER HOUR, FISH SIzE IS tI.5 INCHES, AND OXYGENCONTI,N1' oF INFLOW WATER I].5 PAR'IS PL,R MILLIONPOUNDS PER SqUARE INCH (PSI).IPPM). WATER PRESSURE,S AREWATI']R PRESSUREHIUII l2r Pslll.u\\ il.i PsliFish weight (pounds)Pounds/cubic footPounds/gpmTotal ammonia (ppm)Dissolved oxygen (ppm)100 200 2501.4 2.U 3.5l0 20 250.21 0.44 0.807.5 6.5 5.23004.3ll00.u95.1100 200 2501..1 2.8 3.5l0 20 250.21 0.4,1 0.7,15.8 4.3 3.2food and excrement toward the center for removal through the outletscreen. velocity should never be great enough to cause fish to drift withthe current. Velocities for small fry may be so low that the tank does notself-clean and it will be necessary to brush accumulations of waste to thecenter screen.Oxygen consumption per pound of fish is higher in circular tanks thanin troughs and raceways. This difference may be due to the increased energydemand created by the higher water velocity in the circular tank.SWEDISH PONDThe Swedish Pond was developed specifically for Atlantic salmon. It issquare with rounded corners and its operation is very similar to that of acircular tank. Water is supplied through a pipe at the surface of the water.Waste water leaves the tank through a perforated plate in the center of theunit and the water level is controlled by a standpipe outside the wall of thetank. This design provides a large ratio of surface area to water volume;some fish culturists feel that Atlantic salmon require more surface area asthey do not stack over each other like other salmonids.RECTANGULAR TANKS AND RACEWAYSOriginally rectangular raceways were elongated earthen ponds. Such pondsrequired considerable maintenance because weeds and plants grew alongthe banks and the pond walls eroded. Irregular widths and depths resultedin poor water flow patterns.Rectangular tanks or troughs generally are used for rearing small fry andfingerlings in the hatchery building (Figu.e lg). These can be made ofaluminum, fiber glass, wood, or concrete. Potentially toxic material such as