What is the ruling on someone who performed ablution and prayed one of the obligatory prayers, then found fish scales on a part of the body that prevents water from reaching it? Does he have to repeat his prayer?

The parts of the body used for ablution (wudu') must be washed, in compliance with the words of Allah Almighty: (O you who have believed, when you rise to [perform] prayer, wash your faces and your forearms to the elbows and wipe over your heads and wash your feet to the ankles) [Al-Ma'idah: 6], and in accordance with the actions of the Prophet, peace and blessings be upon him. If there is a barrier between the skin and the water that prevents water from reaching it, then the ablution is invalid. This barrier must be removed, and ablution and prayer must be redone, even if the barrier is minor. Some scholars have overlooked minor impediments such as dirt under the fingernail, traces of blood, and dough, while others believe that any minor impediment that prevents water from reaching the skin is excusable by analogy with what is under the fingernail.