HATCHERY REQUIREMENTS 11 



lesser the penetration, the greater the turbidity), but the word is used less 

 formally to imply concentration (weight of solids per weight of water). 



Turbidities in excess of 100,000 parts per million do not affect fish 

 directly and most natural waters have far lower concentrations than this. 

 However, abundant suspended particles can make it more difficult for fish 

 to find food or avoid predation. To the extent they settle out, such solids 

 can smother fish eggs and the bottom organisms that fish may need for 

 food. Turbid waters can clog hatchery pumps, filters, and pipelines. 



In general, turbidities less than 2,000 parts per million are acceptable for 

 fish culture. 



ACIDITY 



Acidity refers to the ability of dissolved chemicals to "donate" hydrogen 

 ions (H^). The standard measure of acidity is pH, the negative logarithm 

 of hydrogen-ion activity. The pH scale ranges from 1 to 14; the lower the 

 number, the greater the acidity. A pH value of 7 is neutral; that is, there 

 are 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 can 

 live in waters of more extreme pH, even for extended periods, but at the 

 cost of reduced growth and reproduction. Fish have less tolerance of pH 

 extremes at higher temperatures. Ammonia toxicity becomes an important 

 consideration at high pH (Chapter 2). 



Even within the relatively narrow range of pH 6.5-9.0, fish species vary 

 in their optimum pH for growth. Generally, those species that live natural- 

 ly in cold or cool waters of low primary productivity (low algal photosyn- 

 thesis) do better at pH 6.5-9. Trout are an example; excessive mortality 

 can occur at pH above 9.0. The affected fish rapidly spin near the surface 

 of the water and attempt to leave the water. Whitening of the eyes and 

 complete blindness, as well as fraying of the fins and gills with the frayed 

 portions turning white, also occur. Death usually follows in a few hours. 

 Fish of warmer climates, where intense summer photosynthesis can raise 

 pH to nearly 10 each day, do better at pH 7.5-9. Striped bass and catfish 

 are typical of this group. 



ALKALINITY AND HARDNESS 



Alkalinity and hardness imply similar things about water quality, but they 

 represent different types of measurements. Alkalinity refers to an ability to 

 accept hydrogen ions (or to neutralize acid) and is a direct counterpart of 

 acidity. The anion (negatively charged) bases involved mainly are car- 

 bonate (CO3 ) and bicarbonate (HCO3 ) ions; alkalinity refers to these 



