RiverFish

Bullhead · Cottus gobio

Bullhead in the River Mimram

Largest measured bullhead: 11 cm

The largest bullhead measured in Environment Agency surveys of the River Mimram was 11 cm, recorded at Codicote restoration middle fully quant on 28 February 2007.

Across 1,439 measured bullhead, the median measured length was 6.1 cm.

Surveyors recorded weights for 103 bullhead. The median was 0.2 oz (0.005 kg) and the largest recorded weight was 0.5 oz (0.014 kg).

RiverFish uses Environment Agency survey measurements rather than rod-and-line angling records. These figures show fish measured during EA surveys of the River Mimram.

See bullhead records across England →

Most recent observation7 May 2026Chandlers End, Mill Farm
Largest measured bullhead
11 cm
Median length
6.1 cm
Fish measured
1,439
Survey locations
27

Individual EA measurements

Largest measured bullhead

The largest individual measurements in this river and species dataset. Equal measurements are retained as separate surveyed fish.

LengthSurvey dateSurvey locationSurvey ID
11 cm28 Feb 2007Codicote restoration middle fully quant104616
11 cm27 Feb 2007Codicote restoration u/s104610
10.6 cm5 Feb 2019Codicote Station 1156119
10.5 cm27 Feb 2007Codicote restoration u/s104610
10.4 cm5 Feb 2019Codicote Station 1156119
10.4 cm27 Feb 2007Codicote restoration u/s104610
10.3 cm26 Feb 2007Duck Trap Wood104562
10.2 cm13 Feb 2019Sherrardswood School156122
10.2 cm28 Feb 2007Codicote restoration middle fully quant104616
10.1 cm26 Feb 2007Duck Trap Wood104562

Lengths are direct survey measurements. RiverFish does not estimate fish weights from length.

Explore the river

Where bullhead were found

Each point marks a survey location with at least one bullhead record.

Choose a point on the map to see what was recorded there.

Map points are approximate and don’t show fishing access. Check local permissions before visiting.

Place surveyedFirst recordedLast recordedVisits finding bullhead
Chandlers End, Mill Farm15 May 20087 May 20265
Tewin Flyfishers3 Oct 200725 Sept 202517
Panshanger quarry15 Jun 20062 Sept 202518
Upstream Tewin Fly Fishers3 Oct 20233 Oct 20242
Singlers Marsh8 Oct 201426 Sept 20242
Codicote restoration middle fully quant28 Feb 200726 Sept 20243
Duck Trap Wood26 Feb 200730 Aug 20244
Rose Farm13 Jul 200628 Aug 20243
Sherrardswood School12 Jul 20175 Apr 20235
Fulling Mill12 Jul 20174 Apr 20235
Codicote Station 111 Jul 20174 Apr 20236
Welwyn Allotments5 Mar 202011 Aug 20212
Welwyn High Street10 Aug 202110 Aug 20211
Tewin flyfishers middle8 Oct 201523 Sept 20193
Tewin Archers8 Oct 201523 Sept 20194
Codicote Station 211 Jul 20176 Feb 20193
Codicote restoration u/s27 Feb 20076 Oct 20122
Panshanger quarry broadwater bypass channel22 Oct 201021 Sept 20112
Codicote restoration d/s1 Mar 20071 Mar 20071
Codicote restoration middle fixed effort28 Feb 200728 Feb 20071
Rye end cottages12 Jul 200626 Feb 20072
Upstream Panshanger weir16 Jun 200616 Jun 20061
Codicote bottom farm14 Jun 200614 Jun 20061
u/s Tewin Bury farm13 Jun 200613 Jun 20061
School/corn mill13 Jun 200613 Jun 20061
Tewin Bury Farm19 Nov 200319 Nov 20031
Cole Green Way Farm14 Oct 200314 Oct 20031

Choose a point or table row to see the location. More survey visits can mean more records, but not necessarily more fish.

2003–2026

Survey records by year

Each bar shows how many survey visits recorded bullhead that year.

Fish measured by surveyors

Measured length distribution

See how the 1,439 measured fish were spread across different length ranges.

Smallest
2.4 cm
Lower quarter
5.2 cm
Median
6.1 cm
Upper quarter
7.3 cm
Largest
11 cm

Lengths are direct survey measurements rather than anglers’ catches.

Fish weighed by surveyors

Measured weight summary

Recorded weights were available for 103 bullhead. This is a subset of the measured fish and may not represent the whole population.

Lightest
0 oz (0.001 kg)
Lower quarter
0.1 oz (0.0035 kg)
Median
0.2 oz (0.005 kg)
Upper quarter
0.3 oz (0.0075 kg)
Heaviest
0.5 oz (0.014 kg)

These are direct individual weights recorded by Environment Agency surveyors. Combined bulk weights are not included.

More fish in this river

Explore the River Mimram

Compare other species with enough survey and measurement data for a detailed page.

Brown / sea trout Stone loach 3-spined stickleback Minnow 10-spined stickleback Grayling

Before you fish

Good to know

These are past survey records, so the fish present today may be different. Map points are approximate—check local access, permissions and fishing rules before visiting.

Learn how RiverFish uses the data →