The direction of sampling bias when hooking fish from a sea cage: case study of fluke monitoring in Australian farmed Yellowtail Kingfish (Seriola lalandi)
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1
The University of Adelaide, School of Animal and Veterinary Sciences, Australia
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2
Future Fisheries Veterinary Services, Australia
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3
Flinder University / CleanSeas , Australia
Purpose: The Australian Yellowtail Kingfish (Seriola lalandi, YTK) farming industry routinely monitors the burden of skin fluke (Benedenia seriolae, SF) and gill fluke (Zeuxapta seriolae, GF) in fish cages to make treatment decisions. Up to 10 YTK are conveniently captured using hook and line from the side of the cage and flukes are collected and counted. It is generally believed that hooking caged fish tends to select the fast swimming, dominant, and healthier fish. This is expected to result in an under-estimation of parasite prevalence and burden which could mislead or delay intervention. However, the presence and direction of a sampling bias when hooking YTK has not been investigated before.
Methods: Individual weight, fork length and fluke counts were compared between 100 hooked and 100 seined YTK, assumed to be a fair representation of the study cage population.
Results: Hooking increased by almost 6 times the probability of sampling YTK of a weight and length in the lowest 5th percentile of the cage (RR=5.75, p<0.001). These low end fish had on average an extra 32 juvenile and 6 adult GF per kg of fish and an extra 3 juvenile and 0.4 adult SF per kg of fish, compared to the rest of the population (p<0.05).
Conclusions: Hooking biased sampling towards the smallest and most heavily infested fish resulting in an over-estimation of parasite burden in the study cage.
Relevance: In Australia, a short rod is used to hook YTK which mainly access the smaller fish swimming on the edge of the cage. Hooking methods accessing fish from the centre of the cage may select a different category of fish. In the instance where the cage population is very homogenous, sampling bias may be less severe. More cage scenarios with different parasite burdens and fish profiles should be investigated to better predict the presence and direction of the bias.
Keywords:
Sampling,
Bias (Epidemiology),
Ectoparasitic Infestations,
Aquaculture,
yellowtail kingfish
Conference:
AquaEpi I - 2016, Oslo, Norway, 20 Sep - 22 Sep, 2016.
Presentation Type:
Oral
Topic:
Aquatic Animal Epidemiology
Citation:
Caraguel
C,
Fensham
J,
Landos
M,
Bubner
E and
D'Antignana
T
(2016). The direction of sampling bias when hooking fish from a sea cage: case study of fluke monitoring in Australian farmed Yellowtail Kingfish (Seriola lalandi).
Front. Vet. Sci.
Conference Abstract:
AquaEpi I - 2016.
doi: 10.3389/conf.FVETS.2016.02.00041
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Received:
30 Apr 2016;
Published Online:
14 Sep 2016.
*
Correspondence:
Dr. Charles Caraguel, The University of Adelaide, School of Animal and Veterinary Sciences, Roseworthy, South Australia, 5371, Australia, charles.caraguel@adelaide.edu.au