Fish Hatchery Management - fisheries & aquaculture

HA I CHlll{Y ()PliRAl'l()N..S 107At)\llNISlR:\ll()N F()l{ t's1.. wllH f()()l) FIsH. ll.Bl{t AR\'. l1)7ti. S()LlR('1.: l\ll.\'l.lt l. I\I'PI-IC1'I I()\I{A I I.]S0.1 ir.O pprn2.i pounds/acre0.5 2.0 ppmI :] ppnr0..)'2.() ppmll0 10 pounds/(n..c)13 I ir pounds/acre\1()t)u()FACt',l t()NNonsystemicNonsy ste micI'robabllnons,VstemicSl stemicS) stem icc()NlNlt.tN1 S1'I-imit is onc part per nillion lorcopper complexes, butCuSO*'5H20 and basic coppercarbonate are exempted fromthe limitInterim Iimit rn potubl,'sater is0.0I part per nillionInterim limit in potablt rrater i.0.2 part per millionUpper limits are l2 parts pcr mil'lion in raw fish and 0.01 partper million in potable $'ater.Upper limit in raw fish and shelllishis I part per million.oxygen capacity: less oxygen dissolves in water at higher temperatures' Ithas an indirect effect on oxygen circulation: as temperature rises, water becomesmore difficult to mix. If temperatures rise high enough, and the wateris deep enough, the pond may stratify into an upPer' warmer, windmixedlayer and a lower, cooler, poorly circulated layer. In such cases, littlewater moves across the thermocline separating the two layers. Theupper layer receives, and keeps, most of the new oxygen (chiefly from photosynthesisby phytoplankton); the lower layer receives little new oxygen,and loses it-sometimes completely-to respiration (chiefly by bacteria).Several pond management techniques attempt to ovelcome the effects suchtemperature-induced stratification has on the oxygen suPply.It is easy to see why pond-oxygen problems are more acute in summerthan in autumn, winter, and spring. when the water is cool, it can dissolvemore oxygen, and it is more easily mixed by wind action to the pond bottom.Photosynthesis is less, but so is respiration, and photosynthetic oxygenis kept in the pond.In contrast, water circulation is constrained in summer' In the upperlayers, especially in stratified ponds, photosynthesis may be so intense thatthe water becomes suPersaturated with oxygen so that much of the gas is