MARINE AQUACULTURE EFFLUENT MONITORING - METHODOLOGICAL APPROACH TO THE EVALUATION OF NITROGEN AND PHOSPHORUS EXCRETION BY FISH

A wide range of methodologies is used for measurement of excretion by fish and for the evaluation of dissolved nutrient loadings from fish f arms. In order to improve the accuracy and utility of monitoring devic es, two specific apparatus have been adapted and improved: continuous sampling for simultaneous analysis and pooled samples continuous colle ction for later analysis. Provided that pooled samples are stabilized with 10 ml litre(-1) chloroform at ambient temperature after phytoplan kton and organic matter removal, these methods give similar and accura te results when applied to nitrogen-dissolved compounds, and are appli cable to nutritional studies. Applied to soluble phosphate, the pooled method gives, after 72 h storage, results within 5% of the exact valu e. It is suitable for statistical evaluation of nutrient loadings on l arge-scale field studies.