Disaggregation rates of extruded salmon feed pellets: influence of physical and biological variables

摘要

The culture of salmonids in the marine environment has led to concern regarding eutrophication of the water column and sediment from uneaten feed. This study used measurement of mass loss and change in carbon and nitrogen content of feed to quantify material lost from waste feed as a function of physical and biological variables. A laboratory flume was used to measure changes in cooked-extruded salmon feed pellets as a function of pellet size (6.5 and 12.0 mm in diameter), residence time in seawater (0, 24, 48, 72 and 120 h), and flow speed (0, 9.3 and 22.2 cm s(-1) ). The influence of sediment on pellet degradation was also determined. Loss of pellet mass increased with water flow velocity. Smaller pellets eroded faster than larger pellets, losing 32% (6.5 mm) and 21% (12.0 mm) of their mass after 120 h in seawater. The presence of sediment during preconditioning increased the percentage mass loss of the small pellets only. The presence of sediment also resulted in a greater percentage loss of carbon, but not nitrogen, relative to non-sediment samples. These results allow quantitative assessment of the dynamics of feed pellets in the marine environment with respect to prediction of impact from salmon culture.