Fish Tissue Sampling Methodology

If fish are being raised on or in close proximity to the hot spot, tissues should be collected for chemical analysis. Similarly, if wild fish species are known to inhabit surface waters in close proximity to the hot spot, tissues of these fish should also be collected for chemical analysis.

At each fish pond sampled, a maximum of 4 fishes should be collected, and their tissues composited for analysis. The fish collection method is not important; however, care must be taken to ensure that the fish are fresh and were caught in the pond being assessed.

Collected fish must be handled by personnel wearing latex gloves and placed in clean, well-labeled polyethylene bags. Fish must also be dissected within 3 hours of capture. Fork length (mm), whole weight (g), and sex (visual inspection of gonads) are recorded for each specimen in the composite sample. Muscle tissues (skin removed) are collected from the left side of each fish, above the lateral line, and between the dorsal and caudal fins In addition to muscle, the following internal tissues are collected for chemical analysis: liver (entire livers are removed from each specimen), adipose (fat; collected from the viscera), and roe (eggs; if present). Samples must be placed in individual jars for each type of fish tissue, and frozen immediately after dissections are completed.

Pre-sampling Preparation

  • Locate pond to sample
  • Fill out field data sheet
  • Prepare poly-bags, jars and a dissection kit
  • Collect fish

Clean Dissection Kit

  • Put on gloves, rinse gloves with clean water
  • First scrub equipment with sparkleen
  • Rinse with clean water (3×)
  • Rinse with acetone
  • Rinse with hexane

Fish Sample Processing Steps

 

Always use clean equipment and new latex gloves for each fish. Measure the length (mm) and weigh (g) of each fish.

 

Collect muscle samples first. Muscle samples should be collected from the left side of the fish, above the lateral line, and between the dorsal fin and caudal fin. By collecting tissues from above the lateral line, staff will be able to ensure that the scalpel does not accidentally enter the abdominal cavity. If the scalpel enters the abdominal cavity, cross contamination of the muscle sample can occur. The first incision should begin just below the fishes dorsal (top) fin, and run to just above the lateral line.

 

Then make two incisions from the first incision laterally towards the tail of the fish: one just above the lateral line, and the second near the top of the fish.

Remove the skin using a pair of tweezers and the scalpel. Do not touch the dissected area with gloves!
  Make incisions from around the dissected area to free the muscle from the fish. The small bones that hold the tissue in place can be cut through and included in the sample.
  Carefully remove the muscle tissue sample from the fish, making sure no skin or scales are included in the sample.
  Ensure that a sufficient quantity of tissue has been collected to complete the analyses (usually 50 g). The sample size (g) required for analyses will be provided by the laboratory, and should be documented in the field-work-instructions.
  Transfer the sample to a clean lab-supplied jar, taking care not to touch the sample with your hands or any foreign object.
 

Ensure a completed label is securely attached to the sample jar. This label should provide the following information:

  • Sample ID number
  • Sampling Location
  • Date
  • Analyses requested
  • Name of your organization
  • Type of sample (muscle, liver)
  Write the sample name and type of sample on the cap of the jar.

Once the muscle tissue has been collected, the other internal tissues can be collected. Fat samples can be collected by cutting or scraping the fat cells off of the intestinal tract.

Final Steps

  • Ensure that jar and lid are labeled correctly;
  • Secure the label with clear plastic tape around the jar;
  • Ensure all jars are frozen, and put into the cooler; and
  • Ensure that the field data sheet has been completed, including photos, site map sketch and GPS readings.

 

Local fishermen can assist with catching fish
Source: Hatfield Consultants
Hatfield Consultants The World Bank funded by the Canadian POPs Trust Fund through the      
Canadian International Development Agency
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