A target measuring apparatus, comprising: a transducer configured to transmit a transmission wave into water and configured to generate a reception signal based on a reflection wave of the transmission wave on a target; a camera configured to take a picture of the target, the camera and the transducer both facing a first direction (x-direction); and a target measuring system coupled to the transducer and the camera, wherein the target measuring system comprises a weight measuring module configured to measure a weight of the target, characterised in that: the target measuring system comprises a first length measuring module configured to measure a first length of the target based on the reception signal, the first length being measured in a direction parallel with the first direction (x-direction); the target measuring system comprises a target distance measuring module configured to measure the target distance between the camera and the target based on the reception signal; the target measuring system further comprises a second and third length measuring module configured to measure a second length and a third length of the target based on the picture and the target distance measured by the target distance measuring module, the second length being measured in a second direction (y-direction), the third length being measured in a third direction (z-direction) perpendicular to the second direction (y-direction), the second and third directions forming a plane perpendicular to the first direction (x-direction); and the weight measuring module is configured to measure the weight of the target based on the first length of the target measured by the first length measuring module, and the second and third lengths (106b, 106c) of the target measured by the second and third length measuring module. a transducer configured to transmit a transmission wave into water and configured to generate a reception signal based on a reflection wave of the transmission wave on a target; a camera configured to take a picture of the target, the camera and the transducer both facing a first direction (x-direction); and a target measuring system coupled to the transducer and the camera, wherein the target measuring system comprises a weight measuring module configured to measure a weight of the target, characterised in that: the target measuring system comprises a first length measuring module configured to measure a first length of the target based on the reception signal, the first length being measured in a direction parallel with the first direction (x-direction); the target measuring system comprises a target distance measuring module configured to measure the target distance between the camera and the target based on the reception signal; the target measuring system further comprises a second and third length measuring module configured to measure a second length and a third length of the target based on the picture and the target distance measured by the target distance measuring module, the second length being measured in a second direction (y-direction), the third length being measured in a third direction (z-direction) perpendicular to the second direction (y-direction), the second and third directions forming a plane perpendicular to the first direction (x-direction); and the weight measuring module is configured to measure the weight of the target based on the first length of the target measured by the first length measuring module, and the second and third lengths (106b, 106c) of the target measured by the second and third length measuring module. the target measuring system comprises a first length measuring module configured to measure a first length of the target based on the reception signal, the first length being measured in a direction parallel with the first direction (x-direction); the target measuring system comprises a target distance measuring module configured to measure the target distance between the camera and the target based on the reception signal; the target measuring system further comprises a second and third length measuring module configured to measure a second length and a third length of the target based on the picture and the target distance measured by the target distance measuring module, the second length being measured in a second direction (y-direction), the third length being measured in a third direction (z-direction) perpendicular to the second direction (y-direction), the second and third directions forming a plane perpendicular to the first direction (x-direction); and the weight measuring module is configured to measure the weight of the target based on the first length of the target measured by the first length measuring module, and the second and third lengths (106b, 106c) of the target measured by the second and third length measuring module.