Fish Hatchery Management - fisheries & aquaculture

356 FISH HATCHERY MANAGEMENTTemperatureInsulation and ice have been used to control the temperature of transportwater. Ice sometimes is difficultto find during a delivery trip and cancause damage to fish and tanks if used in large pieces. The main advantageof ice is its simplicity;that can break down.it involves no mechanical refrigeration equipmentRefrigeration units are being used increasingly to mechanically controlwater temperature. Such units are expensive and require careful maintenance.Large units easily justify the cost of refrigeration but small systemsrequire additional development before they become economical (Figure111).Because temperature is such an important factor, it should be continuouslymonitored and controlled. Electric thermometers are readily availableand inexpensive, and provide monitoring of temperature from the truck cab.Temperature strongly influences oxygen consumption by fish; the lowerthe temperature, the lower the oxygen consumption. For each l'F rise intemperature, the fish load should be reduced by about 5.60/o; conversely, foreach l"F decrease in temperature, the load can be increased about 5.6%.Thus, if a distribution tank will safely hold 1,000 pounds of 9-inch trout in52"F water, an increase in temperature to 57"F decreases the permissibleload by 27 .8olo (5' x 5.56%), o, to 722 pounds. If the water temperature isdecreased from 52'F to 47"F, the load-can be increased by 27.8% to 1,278pounds.***tFtcunn 111. Aluminum elliptical tank with refrigeration unit mounted at thefront. Aeration is by gas-driven pumps and pure oxygen. Note air scoops (arro*)for CO2 removal on front and rear of tanks. (Ennis NationalFWS.)Fish Hatchery,