Assessment of a displacement technique for the estimation of the biomass of fish in a closed tank

The sensitivity and commercial applicability of an innovative technique that estimates the total biomass of fish in a closed tank was investigated. The procedure involves adding a known quantity of inert marker to a rank of known volume and allowing it to mix completely. The amount of free water in the tank is calculated from the concentration of the marker in the water. This volume is subtracted from the total tank volume, yielding the fish biomass for that tank.

Food Drugs and Cosmetics No. 1 (FD&C Blue No. 1), a triphenylmethane colour, showed better stability than three other candidates.

FD&C No. 1 was determined to be non-toxic to rainbow trout (Oncorhynchus mykiss) and arctic charr (Salvelinus alpinus).

A comparison was made between two physical forms (granular and powder) of FD&C No. 1. The granules gave more accurate results than the powder.

A field survey on four different biomass calculation strategies--mass weighing (standard), dip-net sampling, specific growth rate estimation, and water displacement technique--was performed. Statistical evidence showed that (1) dip-netting yielded random samples, (2) the water displacement technique yielded positively biased estimates of the true fish biomass, and (3) biomass estimation through specific growth rate was reliable. (Abstract shortened by UMI.).