Abstract
Measuring fish population responses to climate change requires timely ecological information, warranting innovative approaches to data collection in fisheries research and management. Fourier transform near-infrared (FT-NIR) spectroscopy is a promising tool to efficiently and cost-effectively obtain multiple types of fisheries data including fish physiological health and energetics that can provide indicators of stock status and environmental change. We tested the applicability of FT-NIR spectroscopy to determine fish physiological state and condition by developing calibration models for morphometric indices of body condition [Fulton’s K and hepatosomatic index (HSI)], biochemical measurements of tissue composition (lipid content and energy density), and a nucleic acid-based index of recent growth (RNA:DNA) of juvenile Pacific cod (Gadus macrocephalus). Calibration models had the best predictive ability for lipid content followed by HSI and energy density, whereas spectral data had weak relationships with Fulton’s K and RNA:DNA. For lipid content, energy density, and HSI, informative spectral regions were primarily associated with carbon-hydrogen bonds in lipid molecules. Additionally, FT-NIR spectroscopy calibration models better predicted lipid content than morphometric measurements that are often used as proxies for measuring energy reserves, indicating that FT-NIR spectroscopy might serve as a more informative index of body condition and energy stores than other rapid methods. Efficient sample analysis by FT-NIR spectroscopy can supplement traditional metrics of body condition and be especially useful for ensuring the availability of monitoring data in support of fisheries research and management.
Highlights
Recent developments in fisheries research and management include the incorporation of ecological information to assess the impacts of environmental and climate change on fish populations and ecosystems
To test the feasibility of using Fourier transform near-infrared (FT-NIR) spectroscopy to measure indices of fish condition, we developed calibration models relating spectral data with traditionally-measured condition metrics for the juvenile stages of an important fisheries species in Alaskan waters (Gadus macrocephalus: Pacific cod) that recently experienced drastic population declines due to environmental change (Barbeaux et al, 2020)
We focused on five metrics that assess differing aspects of condition and that range in required effort and resources for data collection: (1) Fulton’s K, (2) hepatosomatic index (HSI), (3) energy density, (4) lipid content, and (5) RNA:DNA
Summary
Recent developments in fisheries research and management include the incorporation of ecological information to assess the impacts of environmental and climate change on fish populations and ecosystems. Energy density and body proximate composition provide analytical chemistry-based condition indices that are often more informative than rapid methods, but they can be costly, time consuming, and often require the use of hazardous chemicals. Other biochemical metrics such as the ratio of RNA to DNA (RNA:DNA) are appropriate for assessing recent impacts of environmental change or nutritional condition on growth, and may be suitable for young life stages when a large proportion of energy is devoted to growth (Chícharo and Chícharo, 2008). The choice of index depends upon the specific aspects of condition that are measured by each metric, but researchers are often constrained by practicality or resources
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