Embed Size (px)
Citation preview
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!
