Thirteen-year monitoring reveals that Mekong giant catfish (Pangasianodon gigas) has an annual feeding rhythm and a prolonged fasting period

Abstract

The Mekong giant catfish Pangasianodon gigas is endemic to the Mekong River and is one of the largest freshwater fish. This critically endangered species is a popular food for local people and a commercially essential fishery resource. Ecological knowledge of this catfish is required to conserve it. However, its ecology has not yet been well studied. We monitored the food intake of the Mekong giant catfish in a stable aquarium for over 13 years. We analyzed their feeding rhythms and fasting periods. The feeding rhythm (circannual rhythm) of the Mekong giant catfish over 13 years and its temporal variations were revealed. Four of the six catfish showed feeding cycles that extended more than one year (395.7 days). Five of the six catfish showed prolonged fasting periods over 30 consecutive days. These patterns coincide with the wet/dry seasons in Thailand, corresponding to the abundance of catfish food resources (Cladophora spp.). Furthermore, it is suggested that the Mekong catfish has acquired the physiological ability to tolerate a fasting state for about 1 year, possibly because this species may have survived many critical situations in the Mekong River in the past, such as food insufficiency. At the same time, however, this also indicates that the fish is highly dependent on Cladophora spp. as a food item and may not be able to substitute other food items. From these, reductions in food items or feeding habitats for catfish after damming in many places of the Mekong River basin may decrease the population size of this species.