Introduction

Condition factor (K) is an easy, fast and non-invasive assessment tool that can be used in aquaculture to help determine whether fish are properly nourished. Based on the length-weight relationship of a fish, condition factor is expressed as a numerical value (K).

K is a proxy for food fat and body reserves of a fish. Higher K values indicate greater fat and body reserves and a more rotund or round fish. Lower K values indicate less fat and body reserves and a more slender or elongated fish, as length is increasing faster than weight.

K is typically greater than 1.0 in healthy salmonids but can vary by:

  • species
  • strain
  • life stage
  • season

Importance of condition factor

Condition factor is a welfare indicator that can help producers optimize feed management and the nourishment (energy state) of fish. It can help identify welfare issues related to body mass such as emaciated fish and may be used to determine whether fish are able to withstand stressful events such as transportation or fasting.

Sampling fish for condition factor can be a good time to perform broader fish health assessments to identify and score concerns (such as lesions, injuries, fin wear, disease, deformities) and whether or not disease interventions or culling of welfare-challenged fish is appropriate.

Calculating condition factor

Condition factor can be calculated using the following formula:

Condition factor (K) = [W (g) ÷ L3 (cm)] × 100

Where W is the live weight of the fish in grams (g), and L is the fork length of the fish in centimetres (cm). Fork length refers to the length measured from the snout to the fork of the caudal fin (Figure 1).

Table 1 shows the condition factor guidelines for salmonid species.

Table 1. Condition factor guidelines for salmonid species
Fish healthK value
Emaciated< 0.9
Poor condition0.9 to 1.0
Fair condition1.0 to 1.1
Positive performance> 1.1
Possible deformity> 1.6

A rainbow trout with arrows depicting how to measure fork length

Figure 1. Fork length measured on a rainbow trout.

Condition factor example calculations

Well-conditioned

A salmon with a good condition factor on a deck

Figure 2. A salmon with a weight of 1265 g and a fork length of 45 cm.

K = [W (g) ÷ L3 (cm)] × 100

= (1,265 ÷ 453) × 100 = 1.39

K value of 1.39, indicating positive performance and a well-conditioned fish.

Poor-conditioned

A salmon with a poor condition factor on a deck

Figure 3. A salmon with a weight of 279 grams and a fork length of 30.6 centimetres.

K = [W (g) ÷ L3 (cm)] × 100

= (279 ÷ 30.63) × 100 = 0.97

K value of 0.97, indicating a poor condition factor and a potentially emaciated state.

Spinal deformity

A salmon with a spinal deformity on a deck

Figure 4. A salmon with a K value of 1.22. K value of 1.22 is within a healthy range. However, curvature of the spine decreases the fork length of the fish and thus increases the K value, skewing the true condition factor of the fish. This is a welfare issue, and these fish should be culled.

Vertebral deformity

A salmon with vertebral deformity on a deck

Figure 5. A salmon with a K value of 1.89. K value of 1.89 indicates possible malformation. Here, the shortened tail and caudal peduncle decreases the fork length measurement, exaggerating the K value. This is a welfare issue, and these fish should be culled.

Measuring condition factor

Condition factor assessments are typically performed on adult or sub-adult fish where growth distribution has stabilized.

Condition factor measurements are especially important during or shortly after higher-risk events such as fasting, transfers and feeding regimen changes where fish are more susceptible to decreased growth performance.

Being handled and removed from water is very stressful for fish. Sampling for condition factor during routine farm management activities in which fish are already being handled can reduce overall stress.

Condition factor should not be measured:

  • immediately after feeding, as the K value increases with stomach fullness
  • during the spawning season. Fish nearing sexual maturity will tend to have a higher K value than fish at the end of the spawning season
  • when spinal deformities are present (such as scoliosis) as they can skew K values

Considerations for condition factor

Considerations to make when assessing the condition factor of salmonids include:

  • Condition factor varies by season. K value typically decreases during the cold months of winter and early spring and increases during warmer months in summer and early fall.
  • There will always be a certain degree of size variation within a population. When greater than 2% of the population have a condition factor less than 0.9, this represents a serious welfare concern.
  • Keeping historical records of condition factor will help producers and veterinarians identify welfare issues, as well as provide useful information in the event of an animal health emergency.

References

Ahmad, I., and Ahmed, I. 2019. Length Weight Relationship and Condition Factor of Cultured Rainbow Trout, Oncorhynchus mykiss. Journal of Ecophysiology and Occupational Health, 19: 24–27.

Compassion in World Farming. N.A. Improving the welfare of farmed Atlantic salmon at rearing. Food Business. Retrieved April 16, 2024.

Getso, B.U., Abdullahi, J.M., and Yola, I.A. 2017. Length-Weight Relationship and Condition Factor of Clarias gariepinus and Oreochromis niloticus of Wudil River, Kano, Nigeria. Journal of Tropical Agriculture, Food, Environment and Extension. 16(1):1–4.

Government of Canada, F. and O.C. 2004. 5.0 Length and Weight Measurement of Finfish. Fisheries and Oceans Canada. Retrieved April 24, 2024.

National Farm Animal Care Council (NFACC). 2021. Code of Practice for the Care and Handling of Farmed Salmonids.

Noble, C., Gismervik, K., Iversen, M.H., Kolarevic, J., Nilsson, J., Stien, L.H. and Turnbull, J.F. 2020. Welfare Indicators for farmed rainbow trout: tools for assessing fish welfare. FISHWELL. Retrieved April 24, 2024.

Schallich, E., and Gormley, T.R. 1996. Condition Factor, Fat Content and Flavour of Farmed and Wild Salmon. Farm & Food. 6(3):28–31.

Stein, L.H., Bracke, M.B.M., Folkedal, O., Nilsson, J., Oppedal, F., Torgersen, T., Kittilsen, S., Midtlyng, P. J., Vindas, M.A., Øyvind, Ø., and Kristiansen, T.S. 2013. Salmon Welfare Index Model (SWIM 1.0): a semantic model for overall welfare assessment of caged Atlantic salmon: review of the selected welfare indicators and model presentation. Reviews in Aquaculture. 5:33–57.

Utne, K.R., Pauli, B.D., Haugland, M., Jacobsen, J.A., Maoileidigh, N., Melle, W., Broms, C.T., Nøttestad, L., Holm, M., Thomas, K., and Wennevik, V., 2021. Poor feeding opportunities and reduced condition factor for salmon post-smolts in the Northeast Atlantic Ocean. Journal of Marine Science, 78(8): 2844–2857

Author credits

This fact sheet has been authored by Nancy Gao, research assistant – aquaculture, Ministry of Agriculture, Food and Agribusiness (OMAFA), and reviewed by Michael McQuire, aquaculture and aquaponics specialist, OMAFA. Special thanks to Dr. Alexandra Reid, lead veterinarian, OMAFA.