Fish Hatchery Management - fisheries & aquaculture

86 FISH HATCHERY MANAGDMENTFIGURE 33. Marketable size catfish being graded and harvested from a largeearthen pond (Fish Farming Experimental Station, Stuttgart, Arkansas).because this increases loss to predators and the possibility of disease.crowding and the lack of food also will reduce the ability of small fish towithstand handling stress. A fresh supply of water should be providedwhile the fish are confined to the collection basin'Although harvesting the fish crop by draining the pond has the majoradvantage of removing the entire crop in a relatively short time, trapping isanother popular harvesting technique. The advantages associated with trappinginclude better overall condition of the fish, because they are collectedin silt-free waterl reduced injury, because the fish are handled in smallnumbersl avoidance of pond draining; successful harvesting in vegetatedponds; avoidance of nuisance organisms such as tadpoles and crayfish; andreduced labor, as one person can operate a trap successfully. The majordisadvantage to trapping is it does not supply a reliably large specifiednumber of fish on a given date.The most widely used trap on warmwater fish hatcheries is the V-trap(Figure 35). Successful trapping requires knowledge of the habits of thefish and proper positioning of the device. The trap usually is used in combinationwith pond draining; it is positioned in front of the outlet screensand held away from them, against the water current, by legs or some othermeans. The trap is constructed so it floats with about 10% above the water