The Free On-line Aquaculture Dictionary

Biotic Index

Classification groups
Class I Pollution intolerant: These organisms are highly sensitive to pollution.
Class II Somewhat pollution tolerant: These organisms will be found in clean and slightly polluted waterways.
Class III Pollution tolerant: These organisms will be found in polluted, as well as clean aquatic ecosystems

Class I

Biotic Value

Number Found

Class II

Biotic
Value

Number
Found

Class III

Biotic
Value

Number
Found

Stonefly nymph

10

 

Beetle larva

8

 

Midge fly larva

5

 

Mayfly nymph

10

 

Sowbug

8

 

Snails

4

 

Dobsonfly larva

10

 

Scud

6

 

Leech

2

 

Caddisfly larva

10

 

Clams, Mussels

6

 

Aquatic worms

0

 

Riffle beetle

10

 

Crayfish

6

 

 

 

 

Water penny

10

 

Cranefly larva

6

 

 

 

 

 

 

 

Dragonfly nymph

6

 

 

 

 

 

 

 

Damselfly nymph

6

 

 

 

 

 

 

 

Black fly larva

6

 

 

 

 

For example if you find:
25 mayflies 25 x 10 = 250
15 caddisflies 15 x 10 = 150
20 stoneflies 20 x 10 = 200
20 scuds 20 x 6 = 120
20 midge larva 20 x 5 = 100
Total = 820
The total is then divided by 10 (ten) to get the biotic index value
Biotic Index Total = 820 / 10 = 82
Based on the Biotic Index value below, the above water quality is excellent.
 
Biotic Index Score
Excellent >70
Good 60-79
Fair 40-59
Poor <40
Note : Biotic indices are usually regionally specific. The above is only to be used as an example.