starch digestibility

I forgot to mention that African catfish (just like ourselves) can only poorly digest raw starch.
When starch is cooked during the extrusion or pelleting proces the digestibility increases, which means that the fish will have a better feed utilisation and lower FCR.
Cooking of starch starts at about 60°C in the presence of some water, so for example in the preconditioner when steam is added or in the postconditioner if you have. The higher the temperature and the longer the period, the more % cooking will happen.
Starch sources are for example wheat, corn, sorghum, tapioca.
It is this cooking (or gelatinization) that makes your starch bind the pellet bind. It is exactly the same process as baking bread: you mix water with flour and put it in the oven and you have bread. If you put only water without heating or you only heat the flour without mixing water, nothing will happen.