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New Method Could Speed Process of Determining Fish Age and Growth Patterns

Mar 5, 2020

The ability to rapidly detect changes in age and growth patterns for fish populations is crucial to successfully managing them, and a new process studied by S.C. Sea Grant Consortium researchers shows promise for speeding up the previously time-consuming process.

Joseph Quattro, director of graduate studies at the University of South Carolina (USC) School of the Earth, Ocean, and Environment, USC doctoral student Michelle Passerotti, and Joseph Ballenger, a research scientist with the S.C. Department of Natural Resources, examined the effectiveness of Fourier Transform Near Infrared Spectroscopy (FT-NIRS) in predicting the age and growth of juvenile red snapper.

An otolith is held in a person's hand, it is a small triangular piece of bone just a few centimeters wide.

Otoliths are hard, calcium carbonate structures located directly behind the brain of bony fish. S.C. Sea Grant Consortium researchers used otoliths to determine that a time-saving new method for determining age of juvenile red snappers works well. Photo: Florida Fish and Wildlife Conservation Commission.

In previous studies, scanning the bony structures in fish inner ears using FT-NIRS has shown promise in predicting the age of adult fish in terms of years. The research team focused on aging of juvenile red snapper in terms of days rather than years, details that can be especially important in tracking seasonal and environmental effects on species facing pressures from overfishing and climate change.

The age of a fish can be estimated by the measurement of growth increments on ear stones known as otoliths. Changes in otoliths can even be tracked at miniscule incremental scale to track daily growth. But preparing otoliths for daily age estimation using the currently most common process requires dissection, mounting, polishing of microscopic structures, and interpretation by independent readers. It’s challenging and time-consuming.

Testing 153 otoliths, the research team found FT-NIRS scans predicted red snapper ages well. The researchers also determined the most accurate means to present otoliths among several methods. The research indicates FT-NIRS age prediction with red snapper otoliths is not only feasible on both daily and annual scales, but that it can be done with a level of error on par with time-consuming and expensive traditional age estimates. Age determination work that can take several people multiple weeks using the existing method could be done by one person in a 40-hour work week using FT-NIRS.

An article on the study ran in the November 23, 2019 issue of the peer-reviewed journal Fisheries Research. “The capability of FT-NIRS to generate age predictions in a fraction of the time and with improved repeatability relative to traditional methods would save significant costs and improve turnaround time for analysis while maintaining standards for age precision,” the article states.

Update: NOAA Fisheries is vetting this methodology for integration into age production methodologies nationwide. In addition, regional fishery management council recommendations have been made during assessment workshops to pursue the use of FT-NIRS for predicting age of managed species.