I recently started fishing really hard because of needing shining scales for the crafting in Arcanum quest. I noticed when you catch a fish you lose energy. I know it cost energy every time you cast with your bubble, but I also noticed you lose some energy when you catch the fish. Shouldn't you either keep your energy or at least build up your energy every time you catch some fish instead of losing one extra energy point.
You don't use up any energy for simply casting the lure, so you can cast it as many times as you want. You only lose energy when you catch a fish. You also lose half of that energy (rounded down) if you try to catch it and it gets away. However, if a fish bites on a lure, but you don't do anything and it gets away, you don't lose any energy.
You can refill your fishing energy by either waiting (10 minutes for 1 energy), or using an energy elixir. A cheaper, faster way most wizards use is the leveling up method. When you level up, energy, along with health and mana, is restored and increased.