Abstract: An aquatic-animal counting system is provided. The system includes a channel, a linear photographing device, and an operation processing device. A channel is used for a plurality of aquatic animals to pass through. The linear photographing device is used for photographing the aquatic animals passing through the channel to generate at least one image. The operation processing device is electrically connected to the linear photographing device and the operation processing device includes an image processing module. The image processing module utilizes at least one operation rule to analyze the at least one image, so as to calculate a number of the aquatic animals in the at least one image. An aquatic-animal counting method and a recording medium are also provided.