Oldest freshwater fish

As reported in the journal Communications Biology on 23 May 2019, the oldest age-authenticated freshwater fish is the bigmouth buffalo (Ictiobus cyprinellus), a member of the sucker family native to the drainage waters of the Mississippi Basin and Hudson Bay in central USA and southern Canada. Counting annual growth rings (much like ageing a tree) in thin sections of otoliths (earstones), a sample of 386 bigmouth buffalo belonging to 12 different populations revealed that, in multiple cases, as much as 90% of a population was aged 80 years-plus; this far exceeded the previously assumed age cap of 26 years for this species. Thorough bomb radiocarbon-dating analysis was also performed on the otoliths, which validated the ages by proving the growth rings are annual. Thus, bigmouth buffalo became the oldest age-validated freshwater fish. Among all those studied, five were confirmed to be centenarians, with the oldest of them all – a female collected near Pelican Rapids, Minnesota – at 112 years old.

There have been reports of older freshwater fish, such as lake sturgeon (Acipenser fulvescens), however these have been based on analysis of their fins, local hearsay and word-of-mouth, and none of these high age estimates has been validated.

Counting annuli (growth rings) in otoliths – calcium-carbonate features used to help with balance – is currently considered one of the most accurate ways to calculate a wild fish's age. This method was first used to establish the ages of the bigmouth buffalo, before radiocarbon dating was conducted to back up the consistently high age counts being found. The results wielded by both techniques were consistent.

The high percentage of old fish in several populations suggests longstanding reproduction failure, possibly owing to dams built in the 1930s.

The study was a collaboration between North Dakota State University and the University of Hawaii at Mānoa (both USA), led by graduate student Alec Lackmann.