Comparison of different stoichiometric methods for the estimation of proximate biochemical composition of crustacean zooplankton and some considerations on energy transfer to planktophagous fish

In a previous publication (Riccardi & Mangoni 1999) the proximate biochemical composition of some freshwater zooplankton species was estimated from C, H and N content by a calculation method developed by Gnaiger & Bitterlich (1984). The stoichiometric coefficients used by these authors to calculate protein, lipid and carbohydrate fractions were based on reference compounds specifically selected to represent the composition of the soft tissues of fish and molluscs. According to Vollenweider (2000, this issue) the application of Gnaiger & Bitterlich’s equations in estimating zooplankton proximate composition could lead to erroneous estimates, mainly resulting from the fact that carbohydrate is primarily present in the form of chitin. The discussion arising from this question led Dr. Vollenweider to develop a modified calculation procedure and to explore the reliability and the confidence limits of proxy estimates.