A novel approach to determining maturity and reproduction for walleye pollock (Gadus chalcogrammus) using Raman spectroscopy

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Morgan B Arrington, University of Washington, Seattle, WA, Sandra K. Neidetcher, Irina M. Benson and Thomas E. Helser, National Marine Fisheries Service, Alaska Fisheries Science Center, Seattle, WA

Background/Question/Methods
Information on the reproduction of fishes is vital for understanding spawning phenology which can affect ecological processes such as recruitment and trophic interactions. Improved monitoring of maturity and reproduction would allow for a better understanding of variation in phenology and recruitment, especially in response to warming ocean temperatures due to climate change. Maturity status is also key for estimating spawning stock biomass for species assessment and management. Common practices for determining the maturity and reproductive status of teleost fishes include macroscopic evaluation of gonads as well as histological analysis. However, macroscopic evaluation can be biased, and histological analysis is extremely time-consuming resulting in limitations on frequency of data collection and quantity of available data.
Here, we explore a novel approach, Raman spectroscopy, for rapidly differentiating mature and immature ovaries as well as the reproductive stages of walleye pollock based on oocyte biochemistry. Raman spectroscopy is a chemical analysis technique that measures the interaction of light with the chemistry of biological materials such that unique molecular structures result in a measure of absorbance across a range of wavenumbers. We collected spectra from 330 walleye pollock ovaries collected from the Gulf of Alaska in 2017 during the spawning season. Ovary specimens were randomly subsampled using length and maturity stage stratified table and preserved in formalin. Maturity status and reproductive stage were determined using histology.


Results/Conclusions

Immature ovaries differentiated from mature ovaries based on their Raman spectra, as did key reproductive stages based on changes in the biochemistry of oocytes and other ovarian structures detectable by Raman spectroscopy. Specifically, the Raman spectra of vitellogenic oocytes, hydrated oocytes, and post-ovulatory follicles differentiated in the fingerprint region (200-2100 cm-1) based on variation in relative quantities of proteins and lipids. These stages further differentiated from inactive ovaries containing only perinuclear stage oocytes. This demonstrates the skill of this rapid approach in identifying reproductive status of walleye pollock from spectral interrogation of their ovaries. Raman spectroscopy is a non-destructive tool that can be employed en vivo which may also allow for rapid and non-lethal data collection in the field. This study explores the application of an emerging technology in ecological research, vibrational spectroscopy, to increase key biological data available to inform the ecology and management of walleye pollock.