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Biological Monitoring: Fish

Fish have an important ecological role in the overall food web. Fish are an integral part of our environment and natural history and are also an important resource providing food, recreation and economic value. County biologists study fish communities to provide insight on the health and condition of County streams.

Photo of a smallmouth bass on a measuriing stand.

Smallmouth Bass being measured as part of DEPs sampling protocol.

Fish As Biological Indicators of Water Quality

Here are some important reasons why examining and monitoring fish is useful in assessing our local waterways:

Most fish species have long life spans (2 to 10 years or more) and can reflect both long-term and current water resource quality.
Fish continually inhabit the receiving water and integrate the chemical, physical, and biological histories of the waters.
Since different fish species have varying tolerances to pollution, we can characterize stream water quality based on the presence or absence of pollution-tolerant or pollution-intolerant species.
Fish represent a broad spectrum of community tolerances from very sensitive to highly tolerant and respond to chemical, physical, and biological degradation in characteristic response patterns.
Fish have large ranges and are less affected by natural microhabitat differences than smaller organisms such as benthic macroinvertebrates. This makes fish extremely useful for assessing regional conditions.

Learn more about the use of freshwater fish as an indicator of water quality.

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Stream Rating Using Fish Data

Once numbers of individuals are summed for each species present at a stream site, a fish Index of Biotic Integrity (IBI) is calculated based on multiple metrics. The IBI is used to rank the stream in relation to reference stream conditions. To use biological data properly, water resource analysts generally compare the fish data (actually not the raw data but a multi-metric index based on the data) from the stream sites under study, to indices from stream sites in ideal or nearly ideal condition (often called a reference condition). Stream sites are then ranked against the reference condition. This helps DEP set priorities for watershed restoration and improvement.

The fish IBI is averaged with the benthic macroinvertebrate IBI to determine overall stream conditions.

Fish IBI metrics are listed below. A technical, peer-reviewed methodology is used to take raw data and develop them into an acceptable Stream Rating score.

Fish IBI Metrics
Total number of species
Total number of riffle benthic insectivore individuals
Total number of minnow species (cyprinidae)
Total number of intolerant species
Proportion of tolerant individuals
Proportion of individuals as omnivores/generalists
Proportion of individuals as pioneering species
Total number of individuals (excluding tolerant species)
Proportion of individuals with disease/anomalies

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Common Fish in County Streams

The photos below show fish that are commonly found in Montgomery County streams. Sensitive fish are only found in high quality waterways in our County. Pollution-tolerant fish may be found in more streams including those which have been impacted by cumulative or recent pollution.

Sensitive Fish

Blueridge Sculpin

Brown Trout

Northern Hog Sucker

Fish With Intermediate Tolerance

American Eel

Greenside Darter

Longnose Dace

Rock Bass

Rosyside Dace

River chub

Rosyface shiner

Spottail shiner

Yellow Bullhead Catfish

Pollution-tolerant Fish

Blacknose Dace

Brown Bullhead

Creek Chub

Green Sunfish

White Sucker

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Data and Data Requests

Montgomery County has tabular raw fish data and fish narrative summaries from 1994-present for most monitoring sites around the County. Also available are GIS coverages (or maps) showing fish conditions. Maps can be developed to order depending on the request. Submit a request for either raw data or data in maps.

The following tables provide an explanation of the datafields found in our raw tabular data.

FISH Data Table
Field Name	Description
STATION	The station field is a nine character code that identifies the station name. The stations are a combination of the two letter code for the watershed+the two letter code for the subwatershed+ the single digit stream order code+ the sequential reach number.
SPECIES	The official common name of the fish species collected during sampling.
SAMPLE_DATE	The date the station was sampled.
PASS1	Number of specimens collected from the first sampling pass.
PASS2	Number of specimens collected from the second sampling pass.
ANOMALIES	The total number of anomalies.
ANOMALIES_TYPE	The number of anomalies found of a certain type + the two letter code for the type of anomaly found.

FISH Narrative Table
Field Name	Description
Station	The station field is a nine character code that identifies the station name. The stations are a combination of the two letter code for the watershed+the two letter code for the subwatershed+ the single digit stream order code+ the sequential reach number.
Date	The date the station was sampled.
SummaryScore	The final IBI summary score (1-5).
Narrative	Descriptive word to describe the condition of the stream in relation to reference streams. Narratives are either Excellent (>4.5), Good (3.3-4.5), Fair (2.2-3.2), or Poor (<2.2).

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Submit a Data Request

If you are interested in obtaining data or protocols, please contact DEP at askdep@montgomerycountymd.gov. In your request, please provide the following information:

Name, organization (if applicable), phone number, and/or email address
Type of data requested
Time frame requested
Explanation for use of data (helps to personalize the data request)
Preferred method of data retrieval (email, CD by mail, FTP, pick up CD or materials from DEP offices)