Fish Hatchery Management - fisheries & aquaculture

]'RANSPORTATION OF LIVE FISHES 357AmmoniaWhen fish are transported in distribution tanks, their excretory productsaccumulate in the water. Ammonia is the main metabolic product of fishand is excreted through the gills. Total ammonia concentrations can reachl0 parts per million (pp-) or higher in fish distribution tanks dependingon the fish load and duration of the haul. Exposure to ll to 12 parts permillion total ammonia (O.tg to 0. l4 ppm un-ionized ammonia) for 6 hoursand longer adversely affects trout and can reduce stamina.Temperature and time of last feeding are important factors regulatingammonia excretion. For example, trout held in water at 34'F excrete 66'/uless ammonia than those held in 51'F water. and fish starved for 63 hoursbefore shipment produce half as much ammonia as recently fed fish. Smallfish should be starved for at least two days prior to shipping. Fish largerthan 4 inches should be starved at least 48 hours; those 8 inches and largershould be starved 72 hours. If they are not, large losses may occur.Water temperature during shipping should be as low as can be toleratedby the fish being handled. Low temperatures not only reduce ammoniaproduction, but oxygen consumption as well.The effects of metabolic waste products and related substances on warmwaterfish during transportation have received little attention, but most fishculturists agree that excretory products, mucus, and regurgitated food degradewater quality and stress the fish. Cannibalistic species, such as largemouthbass, walleye, and northern pike, obviously should not be starved.Although proper grading for size of fish will reduce cannibalism, it doesnot eliminate it.Carbon DioxideElevated carbon dioxide concentrations are detrimental to fish and can bea limiting factor in fish transportation. A product of fish and bacterialrespiration, CO2 acidifies transport water. Although this reduces the percentageof un-ionized ammonia in the water, it also reduces the oxygencarryingcapacity of fish blood. Fish may succumb if CO2 levels are high,even though oxygen levels are seemingly adequate. Trout appear totolerate carbon dioxide at levels less than 15.0 parts per million in thepresence of reasonable oxygen and temperature, but become distressedwhen carbon dioxide levels approach 25.0 parts per million.Fish transported in distribution tanks are exposed to gradually increasingconcentrations of carbon dioxide. Unless aeration is adequate, CO2 levelsmay exceed 20-30 parts per million. In general, for each milliliter ofoxygen a fish consumes, it produces approximately 0.9 milliliters of CO2.If the CO2 level increases rapidly, as with heavy fish loads, fish become