When investigating our case of a massive fish kill, it would be ideal if we could check every single dead fish. However, this process would be time-consuming, tedious and ineffective. So instead, we take a sample. Sampling is the act of collecting only a portion of material for analytical purposes that accurately represents the entire population being sampled, with respect to stated objectives.

We must collect a representative sample using the appropriate methods, and ensure the integrity of the sample by protecting it from contamination.

Samples are usually taken using a standard sampling unit, which ensures all samples represent the same area/volume of the habitat each time. For example, in the study of water chemistry, the sampling unit would be a single sample water bottle. In the study of a fish parasite, the individual fish would be the sampling unit.

Standard sampling methods include:

Random sampling

Random sampling is performed when the area of study is fairly uniform, very large, and the time for sampling is limited. In random sampling, large numbers of samples are taken from different positions within the habitat.

Systematic sampling

In systematic sampling, samples are taken at fixed intervals.

Fish sampling equipment includes:

  • Holding trays

  • A fish measuring board (metric units)

  • Calipers

  • Shucking knife

  • Balance for weighing

  • Plastic bags for holding individual samples

  • Ice

Water sampling equipment includes:

  • Map of the site to mark where the samples were taken

  • Plastic bottles

  • Thermometer

  • pH meter