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Ontario’s Far North
Fish Processing Manual
FISH EXTERNAL FEATURES:
Brook Trout (Salvelinus Fontinalis):
Dorsal Fin
Adipose Fin
Terminal Mouth
Anal Fin
Pectoral Fin
Pelvic Fin
Caudal Fin
EXTERNAL FEATURES: Walleye (Sander vitreus)
Operculum:
• Used for ageing structures
(lethal sampling) on spiny rayed
fish walleye, bass
Snout:
Overhung vs. non-protruding
Mouth:
•Terminal, sub-terminal,
Inferior, ventral
Dorsal fin – spiny rays:
• used for aging structures on spiny rayed fish (non-lethal)
• bass, walleye
Scales:
• Used for ageing,
• sample area:
Soft Rayed Fish - below dorsal fin and above lateral line
Spiny Rayed Fish – underneath pectoral fin
Lateral Line:
• Count scales along lateral
line for identification
-Complete vs. incomplete
Caudal Peduncle
Pectoral Fin – soft rays:
• Used for aging structures on soft rayed fish (non-lethal)
• Trout, suckers, whitefish
EXTERNAL FEATURES: MOUTH TYPES
Terminal Mouth: tips of upper and lower jaw forming
foremost part of the head; Lake trout, Northern Pike,
Cisco
Inferior Mouth: Mouth below snout overhoung by
snout, not quite terminal – Lake Whitefish
Ventral Mouth: on ventral surface of head – lake sturgeon, longnose sucker white sucker
INTERNAL FEATURES:
How to differentiate Common looking Species:
• Some fish within the same family pose some difficulty in determining what species each is.
• External features is one method used to identify these fish to species some features which are used:
- Mouth and Snout orientation
- Fin Ray counts (dorsal and anal fins)
- Scales along the lateral line (size of scales)
- Fins i.e. adipose fin, forked, square or rounded caudal fin (lake trout vs. brook trout)
- Markings on the body (vermiculations, spots, bars)
- Overall shape of fish
- Colouration
Longnose Sucker (Catostomus catostomus)
9 -11 Dorsal rays
Small scales (91-120 lateral scales)
DESCRIPTION:
Colour
• dark olive or grey to nearly black on back and upper sides, cream to white on lower sides and ventral surface of head and body
chin and mouth often yellow to orange
• reddish band along the middle of each side of the body of breeding females and, especially, males where it extends onto the
snout.
Body
• long and round
Head
•ventral (underneath), sucker mouth
•long pointed snout.
Identification:
• Distinguished from the closely related and more commonly encountered White Sucker by:
• generally darker coloration
• bulbous snout
• smaller size (12"-14")
• noticeably longer snout
• lateral line of 90-117 scales; the White Sucker has less than 85.
Common White Sucker (Catastomus commersoni)
Dorsal fin straight to slightly concave
Usually 10 – 13 rays
Anal fin usually 7 rays
Large Visible scales (less than 85 lateral scales)
DESCRIPTION:
• Noticeably larger scales than longnose sucker
• Snout is shorter than that of the longnose sucker – View diagram of lips and snout above
Colour:
• The back and upper sides are grey, brown or black. The lower sides and belly are cream coloured to white
Body
• Deep bodied fish, adult fish can be thick behind the head towards the dorsal fin
Cisco (Coregonus artedii)
Pointed head
Adipose fin
Check out the angle of the mouth
to the snout.
Even
Terminal mouth - Protruding lower jaw
(snout does not overhang the mouth)
Silvery Fish with blue or black back
Lake Whitefish (Coregonus clupeaformis)
Small Head
Set back
Inferior mouth - snout projects beyond small mouth
Fish Sampling Procedures:
Live Release Sampling Steps:
1.
2.
3.
4.
5.
Identify Fish to species.
Measure fish for Fork Length and Total Length to the nearest millimetre (mm)
Weigh fish using a spring scale or digital balance to the nearest gram (g)
Identify sex if possible (external identification) – only during spawning periods
Collect ageing structures: 1. Scales from all fish (10+ scales from each fish)
2. Dorsal fin (2nd and 3rd) rays from spiny rayed fish (walleye)
3. Pectoral fin rays (1st and 2nd) from soft rayed fish (suckers, trout,
whitefish).
6. Release Fish
Lethal Fish sampling Steps:
1.
2.
3.
4.
5.
6.
Complete steps 1-3,5 from Live Release Sampling steps
Cut fish open from the anus to the gills exposing internal organs
Identify Sex, and Gonad condition
Check Stomach Contents and identify if possible
Remove flesh sample for contaminate analysis by the Ministry of the Environment
Collect Otoliths for aging structures.
FISH MEASUREMENTS: Total and Fork Lengths (mm)
Total Length (mm)
Pinch caudal fin together and take measurement to nearest millimetre from the tip of the snout to the
longest point on the caudal fin
0cm
15cm
30cm
45cm
60cm
75cm
Fork Length (mm)
Take measure to the nearest millimetre from the tip of the snout to the middle of the fork on caudal fin
Example: Total length measurement = 680mm
Fork Length measurement = 600mm
FISH MEASUREMENTS: Total and Fork Lengths (mm)
Fork Length: Fork length measures from the tip of the longest jaw to the center of the fork in the caudal
fin. Measurement is recorded in millimetres (mm)
Total Length: Total length measures the length from the tip of the longest jaw or the end of the snout
to the longest caudal lobe pushed together. Measurement is recorded in millimetres (mm)
Fork Length
Total Length
Fish Weight: Round Weight (RWT)
•Fish are weighed prior to cutting open or removing aging structures
•Fish can be weighed using a spring scale or digital scale if available
•Weight is recorded to the nearest gram (g)
•Spring scales should be maintained (clean and lubricated) and calibrated regularly
•Digital scale should be zeroed before weighing each fish by depressing the tare button
Gonad Identification:
Figure 1. Species = Rainbow trout
Sex = Female (2)
Gonad= Green
Figure 2. Species = Walleye, Sex = male (1),
Maturity = Mature, Gonad = Green
Figure 3. Species = Walleye, Sex = female (2),
Maturity = Mature, Gonad = Green
GONAD IDENTIFICATION (Con’t):
MaleTestes
Figure 4. Immature male gonads – long thin equal width the entire length and gonads are translucent (clear).
The testes usually have a long single dorsal vein running the length of the gonad
GONAD IDENTIFICATION (Con’t):
Air Bladder
Testes
Figure 5. Developing male gonads – gonads are slightly more full and opaque but not white. Still uniform
length and w
GONAD IDENTIFICATION (Con’t):
Ovaries
Figure 6. Mature Female with developing gonads the gonads show some eggs and are slightly clear to
see the appearance of eggs and egg development.
GONAD IDENTIFICATION:
Immature Female Gonads
Immature Male Gonads
Figure 7. Immature Whitefish gonads from both female (left) and male (right). Note: Gonads from Immature Trout
will resemble to these pictures and can be used as a reference. Male gonads are slightly less bulbous and have a
single dorsal vein running the length of the testes. Females have a dorsal vein but is usually branched and less
thick.
MATURITY SCHEDULE: Walleye
Dormant
Spent
Spawning
Fully Developed
Developing
Developing
Immature
Jan
March
May
July
Sept
Nov
Figure 8. Approximate developmental stages of walleye gonads (Duffy, McNulty, Mosindy, 2000)
Jan
MATURITY SCHEDULE: Whitefish and Cisco
Dormant
Spent
Spawning
Fully Developed
Developing
Immature
Jan
March
May
July
Sept
Nov
Jan
Figure 9. Approximate developmental stages of whitefish and cisco gonads (Duffy, McNulty, Mosindy, 2000)
AGING STRUCTURES:
Non Lethal Aging Structures:
• Scales – 10 + scales are removed from correct location based on fish species. Scales are placed in scale
envelope and stored in dry storage area.
• Dorsal Fin Rays – 2nd and 3rd Dorsal fin rays are removed from Spiny Rayed fish.
• Pectoral Fin Rays – 1st and 2nd rays on the Left Pectoral fin are removed. The rays are placed in the same
envelope as the scales. Just try to avoid placing the ray over top the scales in the envelope
Lethal Aging Structures:
• Otoliths – the main ear stones of a fish are collected. The otoliths are cleaned using the back of your hand and
clean fingers. They are stored in a small plastic container stored in a designated storage tray. Lids are left off
for a period of 12 hours or more to dry the otoliths. The otoliths are the most accurate of the aging structures
• Opercles – are part of the gill plate and commonly collected from spiny rayed fish. These structures are
accurate and less time consuming and therefore less costly to age as compared with otoliths.
• Cliethrum – collected from Northern Pike, these aging structures are easily aged and are very accurate for Pike
AGING STRUCTURES: Scale Sample Location
Scale sample area for soft rayed fish below the dorsal fin and above the
Lateral line (brook trout, lake trout, whitefish)
S Scale sample area for northern pike
(soft rayed)
Scale sample area for spiny rayed fish, lift pectoral fin and sample underneath fin (walleye, bass)
AGING STRUCTURES: SCALES (Non Lethal)
1.
2.
3.
Using knife remove the slime by scraping the sample area then clean knife with sponge or cloth (clean
scales are easier to read).
Using tip of the knife remove scales with a flicking motion 10-15 scales are needed for a good sample
(Figure 10).
Turn the knife parallel to the fish and scoop the scales up (Figure 11). Place in provided scale envelope
Figure 10 (left). removing scales with tip of knife
Figure 11 (right) Scooping up scales with knife ready for envelope
AGING STRUCTURES: Fin Rays (Non Lethal)
Spiny Rayed Fish (Walleye, Bass)
Steps:
1. Use 2nd and 3rd Dorsal fin rays
2. Sever membrane between the 1st and 2nd ray and the 3rd and 4th. Cut all the way down to the dorsal muscle of
the fish.
3. Use side cutter and cut the 2nd and 3rd ray as close to the dorsal muscle as possible. Fin rays can be cut
Simultaneously.
4. Place fin rays in scale envelope. Fin rays must be dried for 24h period before being stored.
Note: Fin Rays and Scales can be stored in the same envelope;
Figure 11. 2nd and 3rd Dorsal fin rays being removed with side cutters from a walleye.
AGING STRUCTURES: Fin Rays (Non Lethal)
Soft Rayed Fish: (Trout, Whitefish, Suckers)
Steps:
•
1st and 2nd left pectoral fin rays
•
Be consistent with sampling the same side – Left pectoral fin rays
•
Sever membrane between rays and cut all the way down to the muscle
•
Use side cutters and cut the ray as close to the muscle as possible
•
Place fin rays in scale envelope. Sample must dry for a period of 24h prior to storage
1st and 2nd Pectoral fin rays
Scale Envelopes:
Fill Out:
• Fish #
• Species
• Date
• Location – Lake or River Name
• TLEN – total length (mm)
• FLEN – fork length (mm)
• RWT – round weight
• Sex 1- male 2 – female 9 unknown
• Mat (Maturity) 1 – Immature 2 – Mature
9 – Unknown
• Age Structures (circle) 2 – Scale
4 – Pectoral Rays
7 – Dorsal Rays
A – Otolith
D – Cliethrum
AGING STRUCTURES: Otoliths (Lethal Sampling)
• Otoliths or "fish ear bones" consist of three pairs of small carbonate structures that are found in the head of fish
(we collect only the largest of these bones)
• Otoliths are used by fish for balance, orientation and sound detection. They function similarly to the
inner ear of animals.
• Otoliths accrete layers of calcium carbonate and gelatinous matrix throughout their lives. The accretion
rate varies with growth of the fish – often less growth in winter and more in summer – which results in the
appearance of rings that resemble tree rings. By counting the rings, it is possible to determine the age of the
fish in years. (Wikipedia)
Figure 12. A pair of otoliths that have been removed, cleaned and ready to place in labelled vial
AGING STRUCTURES: Otoliths Removal Steps
1
Step 1. Turn fish over and expose gills
3
Step 3. Remove the gills to expose the
parashenoid bone
2
Step 2. Use the knife and cut the isthmus (gill arch
connection)
4
Parashenoid
Bone
Step 4. Gills removed and parashenoid bone exposed
5
Step 5. Press firmly to cut bone Use one hand on knife handle and the other hand positioned on the blade to
add pressure to assist in cutting the bone. Note position of knife on bone. Approximately ½” back from the
start. The cut is made between the 1st and 2nd gill arch.
6
otoliths
Step 6. After cut is made snap the neck back and expose otoliths notice the placement of hands
7
Otoliths
Step 7. Otoliths are visible
8
Step 8. Extract otoliths using forceps and clean slime away and place in storage vial.
Otolith vials and Storage Box:
• Otoliths cleaned and dried (can use sponge, cloth or
back of hand. Some otolith from different species are
fragile. Handle with care not to drop or break.
• Otolith vial labelled with:
Lake Name
Date
Fish Species
Fish #
• Vials placed in numeric order in the storage box
Aging Structures: Cliethrum (Lethal Sampling)
•
•
Cliethrum are the aging structure used in northern pike. They are easily extracted and once cleaned, the
age can be interpreted by using a magnifying glass.
They are a cost effective way of accurately aging northern pike.
Steps for Cliethrum Removal:
1.
Turn fish on its side with left side facing towards you.
2.
Lift gill plate and exposing the cliethra.
3.
Work index finger under the cliethra and make sure it goes all the way through breaking the skin. Work your
finger to the top of the cliethra exposing the dorsal spine the cliethra.
4.
Pull the cliethra down and outwards separating it from the flesh. Keep pulling downwards until you reach the
the end of the structure.
5.
Once at the end of the cliethra (point) flip the structure and now push the structure upwards to remove the
outside skin.
6.
Flip the whole fish and remove the cliethra from the other side
7.
Optional - Both cliethrum can be cleaned by boiling them in water for approximately 1-2minutes and
scrubbing clean with a scrub brush or toothbrush. The cliethrum should be thoroughly dried before storage.
8.
Alternatively – Both cliethrum can be placed in a labelled whirl pak and placed in cold storage
Aging Structures: Cliethrum Removal Steps
1
2
3
4
Aging Structures: Cliethrum Removal Steps
5
6
Flesh Sample for Contaminants:
• Flesh samples are taken for Mercury (Hg) analysis
Flesh samples are taken from the epaxial muscle located below the dorsal fin and above the lateral line.
flesh samples are boneless and skinless the sample should be between 30g – 50g
• Muscle is placed in a Whirl Pak (provided) and labelled with Sharpie or other type of permanent marker.
Lateral Line
Flesh Sample for Contaminants: Steps
1
Lateral Line
2
1.
2.
3.
4.
5.
Remove a flesh sample from the left side of the fish
Cut along the lateral line of the flesh sample.
Remove the muscle from the skin.
Sample is boneless and skinless.
Place sample in labelled Whirl Pak.
3
Whirl Paks:
Contact Information:
Lee Haslam
Senior Research Technician
Ontario Ministry of Natural Resources
Living with Lakes Centre – Laurentian University
935 Ramsey Lake
Sudbury, ON. P3E 2C6
705-671-3856
Email: lee.haslam@ontario.ca
References:
Duffy, Mark J., Jim L. McNulty and Tom E. Mosindy 2000. Identification of Sex, Maturity, and Gonad Condition of
Walleye (Stizostedion vitreum vitreum) NWST Field Guide FG-05