A study conducted by researchers at the University of Liège on a large population of Japanese giant salamanders – one of the largest amphibians in the world – reveals that above a certain size, a spectacular transition occurs in the diet of this species, propelling it to the top of the river food chain.
The Japanese giant salamander ( Andrias japonicus ) – an endemic and emblematic species of the country – fascinates scientists with its exceptional size, reaching up to 1.5 metres in length. A team of researchers from ULiège in collaboration with the Hokkaido University (Prof. Osamu Kishida) and the NGO The Hanzaki Research Institute of Japan (Dr. Sumio Okada) has just published the results of a pioneering study demonstrating how this species profoundly changes its diet as it grows, moving from secondary consumer to superpredator.
The researchers studied 160 individuals sampled in the Ichi River watershed in Hyogo Prefecture. By combining stomach content analysis with stable isotope analysis of carbon and nitrogen , with the support of the isotopic platforms at the Universities of Liège and Fukushima, they were able to accurately reconstruct the change of these giant amphibians' diet throughout their development.
"The results reveal a spectacular dietary transition , " explains Clément Duret , PhD student at the Laboratory of Ecology and Conservation of Amphibians ( LECA) at ULiège. Young, small salamanders feed mainly on aquatic insects. Their trophic position is similar to that of secondary consumers, an intermediate level in the food chain, as is the case with most salamanders. However, when individuals reach an average length of 62 centimetres, a sudden shift occurs in their diet."
Beyond this critical threshold, researchers have found that salamanders - now giants - turn more towards large prey such as fish, frogs and freshwater crabs. This change in diet is accompanied by a marked increase in their trophic position (their "rank" in the food chain), which climbs to place them at the top of the food chain in their ecosystem. The largest specimens studied, measuring over one metre, occupy a position comparable to that of large aquatic predators such as crocodiles in other aquatic environments!
However, the researchers point out a notable difference between the prey consumed and that actually assimilated by the organism. "Although crabs make up the majority of stomach contents by mass, their actual nutritional contribution is limited due to their indigestible exoskeleton," says Clément Duret. Conversely, fish, although less common in stomach contents, are a much more efficient source of energy for these predators."
This study sheds new light on the evolution of gigantism in amphibians. According to the authors, the ability to capture increasingly larger prey as they grow is a major adaptive advantage that has favoured the evolution of exceptional body sizes within the Cryptobranchidae family. Morphological changes in the skull, particularly progressive ossification and enlargement of the jaw, would allow larger individuals to exploit food resources inaccessible to younger ones, enabling them to reach a higher trophic level while avoiding being consumed themselves.
These discoveries are also important for the conservation of this species, which is endemic to Japan and classified as vulnerable. Understanding the ecological role of the giant salamander and identifying its key prey species will help guide conservation strategies, including the preservation of prey populations in the rivers it inhabits..
Oikos
A giant's appetite: how body size drives the diet and trophic position of the Japanese giant salamander
26-Sep-2025