Old topic, but it's interesting, so what the hell.
Polypterids don't have completely useless eyes, they have extremely good night vision for example, resulting from an almost identical mechanism to that of cats. This also makes their vision blurry, which makes them rely on other senses to a greater degree. The most obvious one is their very keen sense of smell. Their sense of smell however is far from enough, and they use their smell in conjunction with their other senses to catch prey and navigate their environment.
For example, they have a sophisticated lateral line system, used to detect changes in pressure, electrical impulses, and shockwaves in the water. In many ways it's like a sense of hearing, or a radar. Many have also proposed that Polypterids are in fact weakly electric fish, and indeed their heads are covered in electro-receptive pores. These are especially visible in Ropefish. Their lateral line system and electro-receptors is probably what enables them to effictively pinpoint and hunt fast fish. After all their sense of smell is, ultimately, dependant on the flow of water, and it would be almost impossible for them to hunt moving prey by using their noses alone.
Polypterids don't have completely useless eyes, they have extremely good night vision for example, resulting from an almost identical mechanism to that of cats. This also makes their vision blurry, which makes them rely on other senses to a greater degree. The most obvious one is their very keen sense of smell. Their sense of smell however is far from enough, and they use their smell in conjunction with their other senses to catch prey and navigate their environment.
For example, they have a sophisticated lateral line system, used to detect changes in pressure, electrical impulses, and shockwaves in the water. In many ways it's like a sense of hearing, or a radar. Many have also proposed that Polypterids are in fact weakly electric fish, and indeed their heads are covered in electro-receptive pores. These are especially visible in Ropefish. Their lateral line system and electro-receptors is probably what enables them to effictively pinpoint and hunt fast fish. After all their sense of smell is, ultimately, dependant on the flow of water, and it would be almost impossible for them to hunt moving prey by using their noses alone.