The influence of the buoyancy of artemia cysts and shells on the results of determining its quantity in the volumetric method

Abstract

Artemia crustacean cysts occupy one of the most significant places among natural aquaculture feeds. For the production and sale of artemia (at the stage of cysts), it is necessary to standardize methods for assessing the quality of the product. One of the main qualitative characteristics of the biomass of artemia cysts is the number of empty shells. The purpose of this work was to study the accuracy of the volumetric method used in the calculation of empty shells in the biomass of cysts. The method is based on the flotation features of the shells and cysts of crustacean Artemia in fresh water (whole cysts sink to the bottom, and the shells float to the surface). The accuracy of the method was verified by direct shell counting. The data obtained showed a significant deviation of the results of the volumetric method from the direct calculation of the shell in most samples of biomass of cysts harvested on three large commercial lakes of Western Siberia. The detected error of the volumetric method is not systemic, since in half of the samples the volumetric method underestimates the mass of the shell in the biomass of cysts by 1.06–4.23 times, and in the other half it overestimates approximately the same ratio. When calculating the mass of the shell in 1000 kg of biomass of cysts, the error can range from 1.28 to 19.38 kg. The main reasons for the distortion of the results when using the volumetric method are that cysts can have positive buoyancy in fresh water, and empty shells in some cases sink to the bottom. The reason for positive buoyancy may be a change in the individual properties of cysts under the influence of various environmental factors. In laboratory studies, in order to determine the qualitative characteristics of the biomass of cysts, it is more appropriate to use the method of direct shell counting.