Ah Ji explains that each fish has both good parts (the lower jaw, stomach, spine) and bad parts, so the prices will naturally vary depending on the quality.
阿吉師說，同一條魚有好的部位（下巴、魚肚、背脊），也有不好的部位（尾部通常最乾澀），等級不同，價位自然也不相同。