Aquaculture Feed Calculator

Two numbers govern the feed budget of a fish farm. The daily ration is a percentage of standing biomass, so 1,000 tilapia averaging 250 grams represent 250 kilograms of biomass and a 3 percent rate means 7.5 kilograms of feed per day, split across two to four feedings. That percentage falls steeply with size: fry and fingerlings may take 8 to 10 percent of body weight daily while market-size fish take 1 to 2 percent, because relative growth rate and surface-to-mass ratio both decline. The second number is the feed conversion ratio, kilograms of dry feed divided by kilograms of live weight gained. Modern extruded diets give roughly 1.1 to 1.3 for salmon and trout, 1.5 to 1.8 for tilapia and channel catfish, and near 2.0 for carp in semi-intensive ponds. Because feed is typically 40 to 60 percent of variable cost, a 0.1 improvement in conversion is worth more than most other management changes. Both numbers depend on temperature, since fish are ectotherms whose metabolic rate tracks the water. Tilapia feed strongly between about 25 and 32 degrees C and nearly stop below 18; salmon do best around 12 to 16 degrees C and become stressed above 20. Feeding at the same rate outside the optimum wastes feed and fouls the water. Dietary protein is matched to feeding habit, roughly 40 to 50 percent for carnivorous salmonids, 28 to 35 percent for omnivorous tilapia and catfish, and less for herbivores, with juveniles needing more than adults. Protein beyond requirement is deaminated and excreted as ammonia, raising cost and degrading water quality at once. Published ratios also assume good conditions: dissolved oxygen below roughly 3 milligrams per liter suppresses appetite, and a biological conversion ratio ignores mortality, so the economic ratio a farm actually pays for is always worse than the tabulated value.

Fish culture is ancient, with carp ponds documented in China more than two thousand years ago and monastic ponds throughout medieval Europe, but those systems relied on natural productivity and farm waste rather than formulated feed. Scientific fish nutrition began with trout hatcheries in the late nineteenth and early twentieth centuries, which fed ground slaughterhouse offal and liver, a practice that spread disease and polluted raceways. Arthur Phillips and colleagues at the Cortland hatchery in New York worked through the 1940s and 1950s on defined trout diets, establishing energy and protein requirements and producing the widely copied Cortland formulations. The practical breakthrough came with pelleting. The Oregon Moist Pellet, developed around 1960 through work involving the Oregon Fish Commission and researchers at Oregon State University, replaced raw fish with a stable pelleted ration for salmonids. Dry expanded and later extruded pellets followed in the 1970s and 1980s, and because extrusion allows high inclusion of oil, feed conversion ratios in salmon farming fell from well above 2 to near 1.2 within a generation. Requirement data were consolidated by the United States National Research Council, which published nutrient requirement volumes for warmwater and coldwater fishes and revised them in 1993 and again in 2011 as Nutrient Requirements of Fish and Shrimp. Since the 1990s the dominant research push has been replacing fishmeal and fish oil with plant proteins, rendered by-products, and more recently insect meal and algal oils, driven by the limited supply of forage fish.