Fish Hatchery Management - fisheries & aquaculture

N U'fRI'fI()N AND }EEDING 211rate, measured as gain in wet body weight or gain in length, increases to amaximumand then decreases as temperatures approach the upper lethallimit. The best temperature for rapid, efficient growth is that at which appetiteis high and maintenance requirements (or the energy cost of living)are low.For every ltJ"F increase in water temperature, there is a doubling of themetabolic rate and, as a result, an increase in oxygen demand. At the sametime that oxygen demand is increasing at higher temperatures, the oxygencarrying capacity of the water decreases. The metabolic rate of the fish increasesuntil the critical oxygen level is approached. Just below this point,the metabolic rate decreases.Temperature is a very important factor in establishing the nutrient requirementsof fish. To deal with this problem, the National ResearchCouncil (NRC) reports Standard Environmental Temperatures (SET) forvarious species of fish. Suggested Standard Environmental Temperaturesare 50'F for salmon, 59'F for trout, and 85'F for channel catfish. At thesetemperatures the metabolic rate for these fish is 100'11,. Caloric needsincrease with rising water temperatures, resulting in an increase in thefishes' appetite. The fish culturist must, therefore, adjust the feeding rate orcaloric content of the feed to provide proper energy levels for the variouswater temperatures. Failure to make the adjustment will result in less thanoptimal growth and feed wastage.SPECIES, BODY SIZE, AND AGT]Within the ranges of their optimal water temperatures, the energy requirementsof warmwater fish are greater than those of equally active coldwaterfish of the same size. At the same water temperature, coldwater fish consumemore oxygen than warmwater fish, indicating a higher metabolic rateand greater energy need. Carnivorous fish have a higher metabolic ratethan herbivorous fish because of the greater proportion of protein andminerals in their diet. Even though fish efficiently eliminate nitrogenouswastes through the gills directly into the water, more energy is required forthe elimination of wastes from protein utilization than from fats and carbohydrates.Species that are less active have lower metabolic rates andenergy requirements for activities than more active ones. In general, theenergy requirements per unit weight are greater for smaller than for largerfish. Fish never stop growing, but the growth rate slows as the fish becomesolder. The proportional increase in size is greatest in young fish.PHYSIOLOGICAL CHANGESSpawning, seasonal, and physiological changes affect the rate of metabolism.Growth rate becomes complicated with the onset of sexual maturity.