Evaluation of Direct and Indirect Techniques for Measuring Absorption Efficiencies of Sea Urchins (Echinodermata: Echinoidea) Using Prepared Feeds

Measurement of absorption efficiencies is essential for evaluating feeds for the culture of marine invertebrates. There are currently several direct and indirect techuiques that may be used for measuring absorption efficiencies in sea urchins. Three of these methods were evaluated and compared. Based on this evaluation, the conditions under which each technique should be used are reviewed. Direct measures require complete fecal collection and should not be used for estimating absorption efficiency. Ash can be used as a marker to estimate absorption efficiencies under most circumstances, but absorption efficiencies tend to be overestimated as the inorganic fraction decreases slightly with passage through the gut. Chromic oxide can only be used as a marker for estimating absorption efficiencies when complete fecal collection is made, as it may pass through the gut at a different rate than the rest of the egesta.