Can watercress farming impact chalk river fish populations? · 2018-05-01 · Thank you for...

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!

Thank you for listening

Any questions?

A.White2@brighton.ac.uk