Fish Hatchery Management - fisheries & aquaculture

FISH HATCHERY MANAGEMENTtemperature drop from 50' to 46'F would have an increase in Flow Indexfrom 1.50 to 1.80, because the metabolic rate of the fish normally woulddrop and the oxygen concentration would increase with a drop in watertemperature. The reverse would be true with a rise in water temperature.Although Tabk I is useful for planning and estimating preliminarl carrying capacityin a trlut or salmon hatchery, it should be considered only as a guide andspectfic Flow Indexes ultimately should be deueloped at each indiaidual hatcherl.The table is based on oxygen levels in the inflowing water at or near100%r saturation. If a rise or drop in oxygen occurs' there is a correspondingrise or drop in the Flow Index, proportional to the oxygen aaailable forgrowth (that oxygen in excess of the minimum concentration acceptable forthe species of fish being reared).Example: There is a seasonal drop in oxygen concentration from 11.0 to8.0 parts per million (ppttt) lt the water supply of a trout hatchery, and theminimum acceptable oxygen concentration for trout is 5.0 ppm. The FlowIndex has been established at 1.5 when the water supply contained 11.0ppm oxygen. What is the Flow Index at the lower oxygen concentration?(t) Wlttr 11 ppm oxygen in the water supply, there is 6 ppm availableoxygen, since the minimum acceptable level for trout is 5 pp- (11 ppm-5pPm).(Z) Wittr 8 pp- oxygen in the water supply, there is 3 pp- available oxygen(8 ppm- 5 ppm).(g) fhe reduction in Flow Index is the available oxygen at 8 ppm dividedby the available oxygen at 11 ppm or a 0.5 reduction (e+6).(4) The Flow Index will be 0.75 at the lower oxygen concentration(r.s x o.s).Table 9 presents dissolved oxygen concentrations in water at various temperaturesand elevations above sea level. The percent saturation can be calculated,once the dissolved oxygen in parts per million is determined forthe water supply.Many hatcheries reuse water through a series of raceways or ponds andthe dissolved oxygen concentration may decrease as the water flowsthrough the series. As a result, if aeration does not restore the used oxygento the original concentration, the carrying capacity will decrease through aseries of raceways somewhat proportional to the oxygen decrease. The carryingcapacity or Flow Index of succeeding raceways in the series can becalculated by determining the Percent decrease in oxygen saturation in thewater flow, but only down to the minimum acceptable 0x!8en concentration for thefish species.Calculations of rearing unit loadings should be based on the finalweights and sizes anticipated when the fish are to be harvested or loadings