Catfish have a lot of fatty tissue where pollutants can bioaccumulate.
Many toxic pollutants cannot be detected in water; the levels are below laboratory detection limits. Thus, health hazards from pollutants may not be apparent if only the water is analyzed. Bioaccumulation of pollutants in fish tissue presents the real threat. Pollutants accumulate mostly in fatty tissues. Fatty fish, such as carp, bluefish, salmon and catfish, pose the greatest risk when eaten frequently. Laboratory analysis of tissues provides the best way to test for pollutants in fish. Two sampling techniques, one where the fish remain alive, are employed for these tests.
Instructions
Fish Tissue Sampling and Analysis
1. Obtain a fish tissue sample. Collect fish with gill nets or electrofishing. Kill the whole fill, and then put them on ice, or obtain a fish sample with a fish tissue plug without sacrificing the fish. To do this, insert a biopsy punch into the descaled meaty section of a live fish. Place the sample into a plastic bag or glass container, and then preserve on ice. Cover the wounded area of the fish with antibiotic salve and then release back into the water.
2. Decontaminate your equipment between samples. You must keep your equipment clean to get an accurate representation of pollutant levels. Whether you take live fish or biopsy samples, make sure to rinse the fish with site water to remove sediment, shoreline soil, or boat floor debris before you transport them to the laboratory. Clean sampling techniques will ensure you reveal accurate tissue levels in the laboratory.
3. Bass are lean fish with limited bioaccumulation of pollutants.
Analyze tissue samples. After samples arrive at the laboratory, thaw the fish tissues, and grind and mix the edible tissues to be homogenized for analysis. Two different types of analysis can occur, depending upon potential pollutants in tissues. With one method, you digest tissues with nitric acid and analyze them with atomic spectroscopy, a sophisticated way of seeing the chemical's atoms; after which you perform mathematical extrapolations using the tissues' predigested weight, providing a measurement of pollutants. Gravimetric analysis converts the pollutant, through precipitation or combustion, into the pure chemical compound so it can be weighed to provide an accurate measurement.
4. Consider accumulation factors. Testing of fish tissues will reveal accurate pollutant levels, but health threats result from the accumulation of pollutants. Humans' health issues are most prevalent in children, pregnant women and people with compromised immune systems who cannot adequately process too much fish even with safe levels of pollutants. Safe Harbor Testing, a popular analytic service, tests mercury levels in fish at the supplier and certifies safety for fish sent to market. However, this service notes, moisture loss during transportation can increase mercury levels for some fish that reach market. In other words, frequent consumption of supposedly safe fish will lead to bioaccumulation of pollutants in humans.
5. Follow EPA and FDA fish-consumption advisories. The easiest way to decrease health threats is to limit fish consumption to EPA- and FDA-prescribed frequencies. Both agencies rely on years of testing and analysis that has looked at pollutant levels, cooking processes, consumption rates and metabolic processes to advise on safe species of fish and safe frequencies of consumption. In general, lean fish, such as bass, sunfish and yellow perch, are considered safe.
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