Engineers design tanks for rearing commercial fish to minimize both the use of natural resources (water) and the rearing volume necessary to ensure fish welfare. One key to a well-designed tank is obtaining a reliable estimate of the volume (biomass) of fish reared in the tank. The feasibility of a laser scanning technique for estimating fish biomass was investigated in the Journal of Aqua cultural Engineering (Nov. 2012). Fifty turbot fish were reared in a tank for experimental purposes. A laser scan was executed in four randomly selected locations in the tank and the volume (in kilograms) of fish layer at each location was measured. The four laser scans yielded a mean volume of 240 kg with a standard deviation of 15 kg. From this information, estimate the true mean volume of fish layer in the tank with 99% confidence. Interpret the result, practically. What assumption about the data is necessary for the inference derived from the analysis to be valid?