Rheological characterization of an in vitro model for salmonid chyme to quantify changes in feed composition.

Background: Developments in the production of aquacultural salmonid feeds in the last 20 years have led to extruded diets with extremely low water content and a shift from mainly marine fish based ingredients towards plant content. These changes expose the industry to the vagaries of the highly dynamic plant protein market. Resulting variations in the precise composition of aqua feeds may carry unpredictable consequences for water quality, since some plant ingredients cause undesirable reductions in the mechanical stability of faeces. Dietary supplements known as binders that enhance the stability of faeces have the potential to mitigate these issues, but may also bring negative effects.

Objective and methods: The present study employs an in vitro model to perform the first fundamental rheological characterization of salmonid chyme, and a factorial experiment designed to investigate the impacts of the presence of rheologically active substances.

Results: The highest mean viscosity values were measured for a treatment containing a 2:1 ratio of tara gum:xanthan gum, resulting in chyme four times more viscous than a control formulation containing the same amount of water. Shear resistance was quantified by analyses of slopes fitting the frequency sweep measurements.

Conclusions: These data open a new statistical approach to monitoring the consequences of market-driven changes in aqua feed composition and their impacts on the nutrition, health or performance of farmed fish.