Is it permissible to sell fish feed made from poultry meal from slaughtered chickens in slaughterhouses, knowing that the company previously used fishmeal and plant-based protein sources, and that this shift is common in the industry to reduce reliance on fishmeal?

It is permissible to feed fish manufactured feed made from pure ingredients such as grains, or fish or chicken meal from ritually slaughtered animals, provided that this does not harm humans when consumed.

However, feed made from chicken that was not ritually slaughtered (such as carrion or throttled animals), or feed mixed with blood, is impure (najis) and it is not permissible to feed it to fish or animals that will be slaughtered soon. This is because it makes them "jalalah" (meaning: an animal that feeds on impurities), and a jalalah animal may not be eaten until it has been confined and fed pure foods for a sufficient period for the effect of the impurity to dissipate.

It is permissible to feed an animal impure feed if it will not be slaughtered soon, but rather will remain for a sufficient period afterwards to be fed pure foods. Nevertheless, selling this impure feed is prohibited, because it is common for animals, especially fish, to be fed it until they are consumed, which leads to eating forbidden jalalah.

Therefore, it is not permissible for companies to manufacture or sell impure feed, and it is not permissible for farm owners to purchase carrion for use in feed.

As for ritually slaughtered poultry, it is permissible to include them or their skins in feed if no harm is proven. However, the flowing blood from them is impure and it is not permissible to collect it and include it in feed.