Fish Hatchery Management - fisheries & aquaculture

HA'l CHllRY RE(2U IREMIrNl Sthan hypochlorite, and has been used experimentally with some success. Itis unstable and has to be produced on site (from oxygen, with electrical orultraviolet energy). Ozonated water must be reaerated before fish can livein it. Although very effective against microorganisms, ozone is extremelycorrosive and can be a human health hazard-Treatment of Water for ReuseOften it is feasible to reuse water in a hatchery; some operations run thesame water through a series of raceways or ponds as many as ten times.Any of several reasons can make it worthwhile to bear the added cost ofreconditioning the water. The quantity of source water may be low; thecost of pollution control of hatchery effluent may be high. The price of energyto continuously heat large volumes of fresh source water may limitproduction of fish; continuous quality control and sterilization may beexpensive.A hatchery that uses water only once through the facility is called a"single-pass" system. Hatcheries that recycle water for additional passes bypumping and reconditioning it are termed "reuse-reconditioning" systems.In either system, water that passes through two or more rearing units istermed "reused." Most practical water-reconditioning systems recycle90-95'li, of the water, the supplement of make-up water coming from thesource supply. To be practical, the system must operate for long periodswithout problems and carry out several important functions (Flgure 7).As water passes through or within a hatchery, fish remove oxygen, giveoff carbon dioxide, urea, and ammonia, and deposit feces. Uneaten foodaccumulates and water temperatures may change. This decline in waterquality will lower growth and increase mortality of fish if the water rs recycledbut not purified. A water-reconditioning system must restore originaltemperatures and oxygen concentrations, filter out suspended solids, andremove accumulated carbon dioxide and ammonia. [Jrea is not a problemfor fish at the concentrations encountered in hatcheries.Temperatures are controlled, and suspended solids filtered, in ways outlinedabove for incoming water. oxygen is added and excess carbon dioxideremoved by mechanical aeration. The removal of ammonia is moreinvolved, and represents one of the major costs of recycling systems.The advantage of manipulating rearing environments in a recycle systemhas been demonstrated in the rearing of striped bass fry and fingerlings.They have been reared to fingerling size with increased success when thesalinity of the recycled water was raised to 47 parts per thousand duringthe rearing period. channel catfish also have been successfully reared inrecycled-water svstems.