Fish Hatchery Management - fisheries & aquaculture

HATCHITRYREQUTREME,NTS1llesser the penetration, the greater the turbidity), but the word is used lessformally to imply concentration (weight of solids per weight of water)'Turbiditiesin excess of 100,000 parts per million do not affect fishdirectly and most natural waters have far lower concentrations than this.However, abundant suspended particles can make it more difficult for fishto find food or avoid predation. To the extent they settle out, such solidscan smother fish eggs and the bottom organisms that fish may need forfood. Turbid waters can clog hatchery Pumps, filters, and pipelinesIn general, turbidities less than 2,000 parts per million are acceptable forfish culture.ACIDITYAcidity refers to the ability of dissolved chemicals to "donate" hydrogenions (H+). The standard measure of acidity is pH, the negative logarithmof hydrogen-ion activity. The pH scale ranges from I to l4; the lower thenumber, the greater the acidity. A pH value of 7 is neutral; that is, thereare as many donors of hydrogen ions as acceptors in solution.Ninety percent of natural waters have pH values in the range 6.7-8.2,and fish should not be cultured outside the range of 6.5-9.0. Many fish canlive in waters of more extreme pH, even for extended periods, but at thecost of reduced growth and reproduction. Fish have less tolerance of pHextremes at higher temperatures. Ammonia toxicity becomes an importantconsideration at high pH (Chapter 2).Even within the relatively narrow range of pH 6.5-9.0, fish species varyin their optimum pH for growth. Generally, those species that live naturallyin cold or cool waters of low primary productivity (low algal photosynthesis)do better at pH 6.5-9. Trout are an example; excessive mortalitycan occur at pH above 9.0. The affected fish rapidly spin near the surfaceof the water and attempt to leave the water. Whitening of the eyes andcomplete blindness, as well as fraying of the fins and gills with the frayedportions turning white, also occur. Death usually follows in a few hours.Fish of warmer climates, where intense summer photosynthesis can raisepH to nearly 10 each day, do better at pH 7.5-9. Striped bass and catfishare typical of this group.ALKALINITY AND HARDNESSAlkalinity and hardness imply similar things about water quality, but theyrepresent different types of measurements. Alkalinity refers to an ability toaccept hydrogen ions (or to neutralize acid) and is a direct counterpart ofacidity. The anion (negatively charged) bases involved mainly are carbonate(COrj ) and bicarbonate (HCO, ) ions; alkalinity refers to these