it resembles a bird in the air or a runaway slave, because it is unknown; therefore, its sale is not valid, like milk in the udder or the pits inside dates. It differs from the cases they mentioned, because those are part of the expenses of taking possession, whereas this requires effort in order to make it possible to take possession of it. However, if he has a pond containing fish that can be caught without trouble, and the water is clear so that it does not prevent observing it, then its sale is valid. If it is not possible to catch it except with difficulty and slight effort, similar to the effort required to catch a bird from a tower, then the opinion regarding it is like the opinion on selling a bird in a tower, based on the difference of opinion we mentioned regarding it. If the difficulty is great and the duration of the process is long, its sale is not permitted due to the inability to deliver it and the ignorance regarding the time when delivery will be possible.

Section: If one prepares a pond or a filter to catch fish, and fish ends up in it, he owns it, because it is an instrument prepared for catching, so it resembles a net. If he rents the pond or the net, or borrows them for the purpose of catching, it is permissible, and whatever ends up in them, he owns it. If the pond is not prepared for catching, he does not own the fish that ends up in it because it is not prepared for that purpose, so it resembles his land if wild game enters it or fish ends up in it. Whenever one sets up a net, a snare, a trap, or a hunting device, he owns whatever game falls into it, because it is equivalent to his hand. Likewise, if he sets up blades for hunting and invokes the name of God, and they kill a catch, eating it is lawful for him, and it is as if he had slaughtered it. If something fell into his net or its equivalent, it would be guaranteed by him, so it is known from that, that it is equivalent to his hand. If he prepares reservoirs, ponds, or vessels for rainwater to collect, he owns the water upon it gathering in them, because in the context of preparation, they are like nets for catching. If he prepares a boat for catching, such as one in which a light is placed and brass cymbals are struck so that the fish leaps into it, its being in the boat is like its being in his net, because it has become one of the tools prepared for it; but if he did not prepare it for that, he does not own what falls into it. Whoever reaches it first and takes it, owns it.