SAMPLING CONSIDERATIONS
   

BASIC FISH SAMPLING CONSIDERATIONS

  • Collect quality data.
  • Be as accurate and precise as possible when recording & collecting data (eg. Species, length and weight, location, etc.).
  • Design data sheets to follow the order in which fish are sampled in the field and to make data entry easy (i.e. MS Excel spreadsheet or database).
  • Keep air and water temperatures in mind when sampling fish as fish are very sensitive to temperature changes (i.e. keep water temps in sampling containers the same temperature as stream temps – change as required).
  • Minimize the stress to fish; use clear bags (Ziplocs are great) with fresh stream water to quickly identify juvenile fish (do not overload the bag as too many fish in a small bag will deplete the oxygen content quickly).
  • If fish are hold in a holding bucket for any amount of time, provide cover (i.e. branches) and aerate water (change water, aerate in separate container).
  • Anaesthetize fish when taking measurements and weights.
  • Monitor anaesthetic effects and fish recovery very closely – make adjustments as necessary. Keep notes so your procedures get better over time.
  • Put fish back in the same waters in which they were captured.

 

Basic Juvenile Fish Sampling Equipment

  • Holding bucket
  • Anaesthetic bucket or tub
  • Measuring board
  • Small dip nets (aquarium type, fine mesh)
  • Digital scale to weigh fish
  • Recovery bucket
  • Clove oil (or other fish anaesthetic) and syringe dispenser
  • Thermometer
  • Notebook, technical pencils and sampling forms
  • Prepared sample bottles (if samples are to be taken)
  • Camera and film
  • Ziplock baggies
  • Optional: aeration pump and air diffusion stones
  • Optional: GPS

The best and most simple field equipment, or equipment that is recommended for fry sampling includes: 20-25L (5 gal.) buckets with locking lids for holding and recovery buckets, preferably dark coloured to reduce stress; 4L plastic washbasin-type tubs for an anaesthetic container, preferably white so you can monitor fish closely; commercially purchased fish measuring board (eg. Dynamic Aqua <300mm) or a homemade measuring “board” made from a halved PVC pipe and a glued down ruler (must be smooth and accurate); 0-200g digital scale with +/- 0.1g accuracy (eg. Acculab Pocket Pro 250-B); notebooks should have waterproof paper (eg. Write-in-the-Rain and 6-ring plastic binders) and technical pencils are preferred – a sample data collection form is provided in Appendices; clear poly/plastic sample bottles are preferred to glass (breakability) with Formalin or alcohol preservative and good sealing lids, plus some way of marking samples like tape and a marker – always good to have in your sampling kit even if you are not planning on taking samples; disposable cameras are good to bring or leave in a sampling kit, just in case you run into something weird, remember to record roll#, picture#, and a brief description in your notes – it will be hard to remember weeks later when the film is developed; an aeration pump and air stones are optional as water can be aerated by pouring and shaking (don’t shake buckets with fish in them!), however we have found that a small/portable battery-powered bait-type aerator has worked well with fish recovery. See links for some suggested suppliers.


Basic Fish Handling Techniques

Use these basic techniques to minimize stress while sampling juvenile fish:

  • Keep hands wet at all times
  • Hands must be bare (do no use gloves as they can strip the scales off juvenile fish)
  • Handle the fish as little as possible
  • Avoid having too many fish in sampling buckets (anaesthetic and recovery buckets) to maximize the oxygen content in the water
  • Change the water in the buckets often to maintain oxygen content and temperature
  • Fish must be actively swimming in the recovery bucket before you release them
  • Release the fish into the same waters as you caught them in with plenty of cover (example, shaded areas or areas with woody debris or vegetation) and slow moving water, for example, a pool or a glide

The biggest thing to be conscious of when sampling fish is the minimization of stress caused by capturing, holding and handling. Think like a fish, and try to find ways to reduce stress levels, such as, providing cover from the sun or a quiet place to recover. Take notes and improve your methods over time. Talk to others and compare notes.


Basic Diagram of Fish Features

Basic physical features of fish are shown in this diagram. Please keep in mind this drawing is not a real fish and characteristics in this illustration have been combined and emphasized for demonstration purposes. Characteristics can change in different river systems as well as the intensity of colours may be different for the same species of fish due to different stresses and water conditions. Please see materials found in “References and Resources” and follow LINKS for further information on fish biology.

Basic Length and Weight Measurements

Length measurements:


All length measurements for juvenile fish are taken in millimetres (mm). For fish with forked tails such as, salmon, trout and whitefish, measure the fish from the tip of the nose to the fork in the tail (recorded as Fork Length).



For fish with round tails such as, sculpins, burbot and lampreys, measure from the tip of the nose to the tip of the tail (recorded as Total Length).



Weight measurements:

The weight of juvenile fish is always measured in grams (g), To weigh juvenile fish on a scale, put a small bucket or container of stream water on the scale and tare or zero the scale (the scale should read 0.0 grams). Carefully set the anaesthetized fish in the container and record the weight. Once the fish is weighed, place the fish in the recovery bucket.

click image for larger picture

Basic Recording of Sampling Data

  • Date
  • Crew present
  • Weather and/or environmental conditions (i.e. water stage, in flood?)
  • Hours/times in field (start & stop times, trap set and pull times)
  • Directions to site and method (or how you got there)
  • Location (here’s where a GPS unit would come in handy)
  • Purpose and/or project identification
  • Procedures used
  • Comments (i.e. the type of bait you used to capture fry)
  • Map and/or drawing of site
  • Sampling results (# fry captured per trap, hrs trap was set, lengths, weights, species, and any additional data requested, comments or photographic references)

Think: who, what, where, when, why and how. Be precise and accurate as you can be when recording information, otherwise your sampling data may not be valuable to others. Your written and photographed account of your sampling trip and its results are all you will have when everything is over – make them count. Generally, notes can be classified into two categories: (1) notes on the sampling trip itself, and (2) results from the field sampling (data). Keep hand written notes in a safe place (don’t throw them away!) and try to input data digitally as soon as possible. Remember to back-up all digital data. One good way of doing this is to share it with others!

Additional Notes and Anaesthetic Recipes

Generally speaking, carbon dioxide renders fish unconscious or it “knocks them out” in part by displacing dissolved oxygen in the water, so it can be much like suffocation, and, CO2 lowers the pH in the water – so buffered Antacid is preferred. We recommend using clove oil anaesthetic as it is a true anaesthetic, meaning its active ingredient (eugenol) drugs the fish into unconsciousness, and it is quite easy to use. Other fish anaesthetics like tricane (MS222) are effective but are presently banned in Canada for food fish. Before using recipes or anaesthetizing fish for the first time, check with technicians and biologists and go over your plans with an experienced practitioner. Monitor recovery times and the state of fish very closely. Be respectful of the fish: pay attention at all times and watch for signs of distress, monitor water temps, adjust dosages starting from a low dose, working slowly upwards. Take notes and strive to get better over time. Think like a fish – provide cover from the sun while sampling, and a quiet place for their recovery.


CARBON DIOXIDE (CO2)


Use Alka-Seltzer or Eno™ brand antacid and dissolve 1 to 1½ tablets or roughly 1 heaping teaspoon of the powdered antacid into 4L tub of water, mix thoroughly in water and adjust amounts upwards or downwards with the size of fish and water temperature. Larger fish may require heaver doses and/or longer exposure times. At cooler water temps fry may require heavier doses and/or longer exposure times. Use buffered tablets or power. Monitor effects and recovery times very closely and watch for signs of haemorrhaging (very bad!). Early signs of haemorrhaging include reddening at the edges of gums and around the nostrils, later more serious signs of haemorrhaging include reddening and blood-shot cranium, as seen through the top of the head (fontanelle), which is usually pretty “see-through” on small fry.

CLOVE OIL


Clove oil does not readily dissolve in water and must first be mixed with ethanol to enable the oil to be mixed with water. Pre-mix a solution of clove oil and ethanol at a ratio of 1:10 (i.e. 10ml clove oil to 100ml ethanol, equals 110ml of concentrated solution, or roughly enough to make 75 batches of 4L anaesthetic). Then add the pre-mixed solution to water to achieve concentrations of 20-30ppm (i.e, 1.4ml of the pre-mixed 1:10 clove oil to ethanol solution into 4L of water, equals 30ppm).

The actual formula for calculating the amount of clove oil is:

Larger fish may require heaver doses and/or longer exposure times. At cooler water temps fry may require heavier doses and/or longer exposure times. Store clove oil and clove oil pre-mixture in UV-proof bottle or out of the sun (active ingredients break down in sunlight and solution becomes weaker over time). Use a syringe to measure and dispense the pre-mixture. Look for small quantities of clove oil at your local health food store or by it in bulk from an industrial supplier (See “References and Resources”). Use 95% ethanol in the pre-mixture and obtain a permit from YTG Community Services. You can find the special 95% ethanol at your local territorial agent/government liquor store. Keep in mind that individual liquor stores may not normally stock these items and they may need to be specially ordered – so prepare this well in advance of your planned sampling trip.