Estimating the total length of Mekong giant catfish, Pangasianodon gigas, in an aquarium via stereo‐video shooting and direct linear transformation

The Mekong giant catfish (MGC), Pangasianodon gigas, is one of the world's largest catfish species. Endemic to the Mekong River system, the MGC is critically endangered. Six MGC were transported from Thailand to the Gifu World Freshwater Aquarium (GWFA) in Japan in May 2004. The MGC have not been measured since they were introduced to the GWFA due to the challenges associated with their large size. Traditional methods, such as anesthesia and net‐capture, could harm the fish, potentially reducing the population further. However, understanding the ecology of the species is essential to conservation efforts. Seasonal feeding rhythms and long‐term fasting were previously observed in captive MGCs. To investigate the effect of long‐term fasting on MGC growth, total length measurements are necessary. In this study, we applied a noncontact method to estimate the total length via image analysis. We shot a stereo‐video of free‐swimming MGC in the aquarium tank using two digital video cameras and analyzed the 3D images using the direct linear transformation method. We successfully estimated the total length of each MGC individual without contacting the fish. This accurate estimation method is versatile, simple, and useful in aquarium breeding and is also recommended from the viewpoint of animal welfare because it is a noninvasive method of measurement. The total length of Mekong giant catfish in an aquarium can be estimated via stereo‐video shooting and direct linear transformation, safely without contact. Research Highlights • Total length of Mekong giant catfish (MGC) was estimated in an aquarium tank, using stereo‐video recording and direct linear transformation (DLT) method. MGC can be measured safely without contact, preventing injury and stress. This is a useful method for all fish in terms of improving animal welfare.