Can watercress farming impact chalk river fish populations?
Asa White
School of Pharmacy and Biomolecular Sciences, University of Brighton, United Kingdom
Potential stressors on fish populations from watercress farming
• Suspended solid inputs and siltation
• Nutrient inputs – eutrophication
• Depletion of macroinvertebrate prey species
• Phenethyl isothiocyante (PEITC)?
Phenethyl Isothiocyanate (PEITC) • Gives watercress its ‘peppery’ taste
• Chemical defence against grazing by invertebrates (Newman et al., 1996)
• Produced when tissues of brassicas are damaged – for example when watercress crops are cut and washed
• Laboratory studies have revealed toxic effect on gammarids (Newman et al. 1990)
• Thought to play a role in altering invertebrate populations downstream of watercress farms
• To date there is no published data on impact on fish
Rationale
• Are fish populations downstream of watercress farms impacted by discharges?
• What is the likely cause?
Habitat degradation (increased suspended solids etc)?
Altered macroinvertebrate prey assemblages?
A direct result of PEITC?
Watercress farm sites
St Mary’s Bourne
The Crane at Edmondsham
The Frome at Morton
• The Bourne Rivulet – Vitacress Salads Ltd
• The Crane – Sun Salads • The Frome – The Watercress
Company
Three watercress farms under study. At each farm, four sites are being surveyed twice a year
Surveying Watercress farm
At each site:
• Electric fishing survey (100m)
• HABSCORE habitat survey (suitability for salmonids)
• Invertebrate surveys (3 min kick sample)
• Water quality; dissolved oxygen, conductivity, temperature, pH, suspended solids
• Flow and discharge rates
PEITC Toxicology experiments
Fish embryos used in trials because:
• Developing embryos and early life stages of fish are more sensitive to toxicants than adults
• Chalk stream headwaters important spawning grounds
Species trialled:
• Brown trout (Salmo trutta)
• Common carp (Cyprinus carpio)
• Grayling (Thymallus thymallus) to follow
PEITC Toxicology experiments
Trials exposed embryos (three replicates of 50 eggs) to PEITC at:
o 1µg/L
o 0.1µg/L
o 0.01µg/L
o DMSO solvent control (at same conc as the 1µg/L treatment (1ml/L))
o Water control
Toxicity endpoints:
• Mortality and hatch rates
• Morphological aberrations such as inhibited growth, spinal deformities, fluctuating asymmetry and length/weight ratios
• Behavioural responses to stimulus (DanioVision)
Brown trout eggs at 33 days post fertilisation, just beginning to ‘eye’
Results: Mortality rates (%)
Brown trout Common carp
12 17
28
52
100
0
10
20
30
40
50
60
70
80
90
100
Water control DMSO control 0.01µg L 0.1µg L 1µg L
PER
CEN
TAG
E M
OR
TALI
TY
TREATMENT
16
9
29
61
100
0
10
20
30
40
50
60
70
80
90
100
Water control DMSO control 0.01µg L 0.1µg L 1µg L
PER
CEN
TAG
E M
OR
TALI
TY
TREATMENT
Results: spinal curvature
Brown trout Common carp
0.1 µg/L0.01 µg/LDMSO controlWater control
180
160
140
120
100
80
Treatment
Sp
inal cu
rvatu
re (
deg
rees)
a
a a a b
0.1ug/L0.01ug/LDMSO controlWater control
180
160
140
120
100
80
Treatment
Sp
inal cu
rvatu
re
a a a b
Significant differences in spinal curvature (F3,89 = 11.33, P = <0.001) Significant differences in spinal curvature (F3,132 = 16.11, P = <0.001)
Behavioural responses DanioVison™
• Fish larvae placed into well plate
• Fish tracked in real time using infrared camera
• Light sequence programmed to turn off and on
• Response to swimming behaviour during switch between light/dark recorded
Brown trout alevin movement
Carp larvae movement
Summary of ecotoxicology findings
• PEITC at 1 µg/L kills trout and carp embryos after four 24hr doses
• PEITC exposure at 0.1 µg/L significantly increases, deformities and causes behavioural changes likely to decrease chances of survival
Further work
• Complete further ecotox trials on brown trout and carp to firm-up dataset for publication
• Ecotox trials using grayling (Thymallus thymallus) this spring
• Complete final season of fieldwork this coming spring/summer
• Analyse the complete macroinvertebrate, habitat survey and electric fishing dataset
• Answer the research question
• Complete thesis!