Two algal polysaccharides: alginate and agar and one polysaccharide from fruit, pectin, have been used as food additives in relation to their structure and their rheological behavior, stability and interactions, to generate firm pellets to be employed in crayfish aquaculture. Three diets containing the same amount of nutrients (protein, lipid and carbohydrate) mixed with each of the three different polysaccharides were tested on male freshwater crayfish Cherax albidus growth. The aims of this study were to examine the effect of alginate, agar and pectin, on pellet stability in water, and on crayfish growth. The kinetics of water absorption and solute leaching of pellets were measured by immersing quadruplicate samples of the diets in water for 0.5, 2, 4 and 8 h. After the required immersion time, the samples were recovered, freeze-dried for 24 h and re-weighed.
Recovered liquid was analyzed by Low Angle Laser Light Scattering Technique, which allowed the monitoring of the released particles in water during immersion. At the same time, the crayfish feeding response to firm pellets was monitored in feeding behavior and growth experiments. Our results show that pellets had good water stability, were preferred by crayfish and the presence of polysaccharides positively affected crayfish growth. Indeed, animals fed pellets showed a higher percentage of growth when compared to animals fed a fresh diet. In particular, pectin gave the best results, showing better water stability than alginate and agar and causing the best growth performance. Pellets are relatively low cost and easy to make and they may represent an advantage for those who want to farm crayfish under intensive conditions.