What is the ruling on using edible fish as fertilizer for agricultural land, and is this considered a waste when there are poor people who could benefit from it?

The default rule is that a Muslim is permitted to use what they own of fish and other things in a way that achieves a legally recognized benefit for them, and they are not obligated to prioritize the poor with it. So, it is permissible for them to feed animals and fertilize their farm with fish, and they are not obligated to prioritize the poor. However, it is preferable, if it is possible to combine the benefit of the land and the benefit of the poor, to fertilize the land with the remaining waste and give the meat to the poor.