Streamlined Technology Allows Science Center to Accelerate Fish Fat Studies
Scientists at the Alaska Fisheries Science Center (AFSC) are substantially increasing their research into the amount of energy-rich fat in fish, thanks to a new streamlined method that allows them to more than quadruple the number of fish sampled each day.
Study results, announced Sept. 24, looked at all five species of Pacific salmon, Pacific herring, cod, pollock and capelin. The results produced data that matched what traditional methods produced, validating the sulfo-phospho-vanilllin (SPV) assay method and certified a novel way to measure lipids in Alaska marine fish.
The SPV assay has for some time been studied as a rapid alternative to traditional methods for lipid analysis. Lipids, or fat, have long been regarded by scientists as the most important energy reserve for animals in marine ecosystems. They are more calorie-dense than proteins and sugars and are used to fuel growth.
The total lipid content of fish is widely used as a metric to understand the overall health and condition of a population. Moreover, prey species with higher lipid content contribute to the overall health of the predators that eat them.
Traditional methods for analyzing lipids take a lot of time and produce relatively few results, an average of 15 samples at the AFSC, scientists there said. The new method allows a technician to produce results from 69 samples within the same time frame, generating more data on a faster turnaround for decision-makers to inform fish stock assessments and fisheries management on tighter time scales.
“Good data about fish stocks requires large sample sizes,” said Cody Pinger, lead author and analytical chemist at AFSC. “And in my experience of measuring fish lipids, laboratory methods are usually slow and tedious.”
“For nearly a decade, our group has been working to optimize the sulfo-phospho-vanillin assay, and I’m thrilled to say that we have increased our productivity many-fold while maintaining good accuracy and precision,” he remarked.
The SPV assay has been long studied as a rapid alternative to traditional methods for lipid analysis.
For some species, the entire fish is blended into a uniform mixture; for others, scientists only process the muscle tissue. The sample is extracted into organic solvent, using heat and concentrated sulfuric acid, followed by a reaction with vanillin in the presence of phosphoric acid—hence the name sulfo-phospho-vanillin.
This process generates a final product that is a clear liquid with a pink tint. The darker the pink equates to more lipid in the sample.
From there, the sample is passed through a spectrophotometer, which measures the amount of light absorbed by the sample. This instrument can quantify the amount of lipid in each sample. The 96-well format allows the team to analyze many more samples at once, which streamlines the process and is more efficient than traditional methods.
The chemical reaction between lipids, acid and vanillin is dependent on the specific molecular composition of the fat, which varies between species of fish.
In a perfect world, all samples could be calibrated using a widely available fish oil, but fat from a salmon filet is chemically different from fat from a Pacific cod.
To fine-tune the results of the SPV assay using menhaden oil for calibration, the team developed calibration models for each species analyzed.
