Elevated strontium concentrations in the otoliths and stable isotope values in muscle tissue of river caught
P. krempfi
reflect values characteristic of marine environments. This finally provides support for the long-held suspicion that
P. krempfi is anadromous, i.e. it spends part of its life in the South China Sea.
Z. Hogan, I. G. Baird, R. Radtke & M. J. Vander Zanden, 2007. Long distance migration and marine habitation in the tropical Asian catfish, Pangasius krempfi. Journal of Fish Biology, 71(3): 818–832. Highlights are reported here: "Pangasius catfish is anadromous," by Ng Heok Hee. Practical Fish Keeping, 28 Aug 2007.
For the story behind the collaborative research, read "The Imperiled Giants of the Mekong," by Zeb S. Hogan, Peter B. Moyle, Bernie May, M. Jake Vander Zanden & Ian G. Baird. American Scientist, 92(3): 228.
Excerpt - "...most interesting was the presence of large (meter-long) silver-toned catfish (Pangasius krempfi) in many fishmongers' stalls. Why were silver-toned catfish a surprise? A few years before Hogan arrived in Thailand, Baird had reported that this species could be found in the South China Sea and also in southern Laos. Baird surmised that this migratory catfish might be anadromous, traveling from the marine waters of the South China Sea up the Mekong through Vietnam and Cambodia and into Laos, where they presumably spawned.
His basic theory, along with Hogan's later observation of this species in Nong Khai, Thailand (about 1,600 kilometers upstream of the Mekong Delta), provided impetus for a study of the silver-toned catfish that could better document its travels. [Hogan and Baird]began by carefully examining, of all things, small structures in its ears [the otoliths]"
"Radtke and Kinzie found that otoliths can also indicate events that take place as the animals mature. In particular, the ratio of strontium to calcium in an otolith records whether the fish had been living in salt water or fresh water, because strontium concentrations in the ocean are one to two orders of magnitude greater than in rivers or streams."