Fish Hatchery Management - fisheries & aquaculture

FISH HAI'CHEI{Y MANAGEMENl'several buyers, who find them more attractive if the fish are of uniform sizewithin each lot.A number of commercial graders are available. Mixed sizes of fish mayrequire grading through more than one size of grader. Floating gradingboxes with panels of metal bars on the sides and bottom are commonlyused in fish hatcheries. Spacing between the bars determines the size offish that are retained; fish small enough to pass between the bars escape.The quantity of fish in the grader at any one time should not exceed fivepounds per cubic foot of grader capacity. Small fish can be driven from thegrader by splashing the water inside the grader with a rocking motion.Recommended grader sizes for such warmwater fish as minnows andchannel catfish are as follows:MinnowsChannel catfishSpacing Length Spacing Lengthbetween of fish between of fishbars held bars heldftnches) Gnches) 6nches) Gnches)II(,1l)l() I:-'i,1llt;1li)l'll.l 2l:rI2()lI,) |29l'2iIl,t!(rl10{i1.18l) Irll;('{ri.lJA5(;78A 1]-inch grader will retain J-l-pound channel catfish. Catfish passmost readily through the bottom of a grader and minnows through thesides.Fish Handling and HaruestingHandling of fish should be kept to a minimum to avoid injury and stressthat can lead to disease or death. Losses from handling can be substantial,but they do not always occur immediately and can go unnoticed after thefish have been stocked in natural waters.An adequate supply of oxygen must be provided in the raceway or pondduring harvest, and during transit in containers. Silt and waste materialsuch as feed and feces in the water should be avoided or kept to aminimum. Overloading nets or containers will abrade the skin of the fish.Extremes in water temperature should be avoided in the hauling containersand between rearing units. Sudden changes in water temperature of 6"F or