Potential impact of fish evisceration on the life cycle of Anisakis: an experimental approach
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1
University of Valencia, Cavanilles Institute of Biodiversity and Evolutionary Biology, Spain
Species of the genus Anisakis (Nematoda, Anisakidae) are cosmopolitan nematodes that stand out for their economic and sanitary importance as they can accidentally infect humans and cause allergies (Davey 1971, Marino et al. 2013). The complex life cycle of Anisakis spp. includes cetaceans as definitive hosts and a number of crustaceans, cephalopods and teleost fishes as intermediate and paratenic (transfer) hosts, many of them of great commercial interest.
Health authorities worldwide recommend fish evisceration at sea in order to prevent post-mortem migrations of larvae 3 of anisakis to fish muscle, thus minimizing the infection risk for humans. However, it has been suggested that the removal of infected viscera may cause an increase in the abundance and local concentration of infective stages in the natural environment (McClelland et al., 1990). Since numerous larvae probably end up leaving the removed viscera, the key question is whether these “free” individuals are capable of re-infection. This could happen only if (1) larvae of anisakis are able to survive outside from its host for a long period, (2) fish or cephalopods consume them, and (3) these larvae can re-infect new hosts.
This study investigates these issues through an experimental procedure, divided in three phases. First, a survival analysis was carried out by maintaining free larvae 3 of Anisakis sp. type I (excysted, n=50), obtained from blue whitings (Micromesistius poutassou) in seawater at 12 ºC during 21 days. Second, groups of 10 free larvae were individually offered to 25 seawater-acclimated mollies (Poecilia sphenops). Finally, infection success in mollies was investigated based on the rate of larval establishment. Also, at the beginning and the end of experiments (i) and (iii), morphometrical measures and vitality scores (1-3, min. to max.) of the larvae were taken.
Our results indicated that 90 % of "free" anisakis survived more than 21 days in seawater, from which 10 % did so in optimal conditions of vitality (score 3), despite significantly reducing their length and weight (P<0.01 in a paired sample t-test), i.e., 25% decrease of total length (5.6 ± 3.5 mm) and 50% decrease of biomass (ca. 2.2 mg). Fifteen mollies (83.3 %) naturally fed on anisakis. Many larvae were broken or exhibited damages in the cuticle, but 11.8 % of the ingested larvae established successfully. However, these larvae showed a decrease in vitality and exhibited a significant increase of weight (3.2 ± 0.2 mg) (P<0.01 in a paired sample t-test).
These results suggest that larvae 3 type I of Anisakis is capable of surviving as a free-living stage for extended periods. Furthermore, larvae can naturally be ingested, not only by mollies, but also by large marine teleost species. A recent study on cultured gilt-head bream (Sparus aurata) indicated that fish readily ingested anisakis larvae, which were able to encyst in the mesentery (Herrero-Schell, unpub. data). Interestingly, the infection success was 6% lower than in mollies. In any event, re-infection costs seem to be apparent, at least in mollies, because many consumed larvae were damaged or destroyed due to fish' oral processing, and established larvae exhibited reduced size and vitality.
We conclude that "free-living" larvae of anisakis coming from evisceration or fish discards could lead to the re-entry of a small fraction of viable anisakis larvae in the life cycle. However, the portion of successful larvae would be smaller than what could be assumed a priori, given that free larvae are more vulnerable to abiotic factors and mechanical/physiologic processing of potential new hosts.
Acknowledgements
This study was supported by the project UV-SFPIE-RMD15-314989: “Renovación de Metodologías Docentes” from the University of Valencia.
References
Davey JT (1971). A revision of the genus Anisakis Dujardin, 1845 (Nematoda: Ascaridata). Journal of Helminthology 45: 51-72.
Marino F, Lanteri G, Passantino A, De Stefano C, Costa A, Gaglio G and Macrì, F (2013). Experimental susceptibility of gilthead sea bream, Sparus aurata, via challenge with Anisakis pegreffii larvae. BioMed Research International 2013.4.
McClelland, G., Misra, R., & Martell, D. J. (1990). Larval anisakine nematodes in various fish species from Sable Island Bank and vicinity. Canadian Bulletin of Fisheries and Aquatic Sciences 222: 83-118.
Keywords:
Anisakis,
re-infection,
Poecilia sphenops,
life cycle,
fish evisceration,
Survival,
Micromesistius poutassou,
Fish discards
Conference:
IMMR | International Meeting on Marine Research 2016, Peniche, Portugal, 14 Jul - 15 Jul, 2016.
Presentation Type:
Poster presentation
Topic:
Aquaculture
Citation:
Herrero Schell
J,
Bartolomé Carretero
A,
Fresneda Marzal
M,
Miquel Mazzetti
L,
Torrado Mateo
H,
Fernández Martínez
M,
Aznar
FJ,
Born Torrijos
A and
Montero Royo
F
(2016). Potential impact of fish evisceration on the life cycle of Anisakis: an experimental approach.
Front. Mar. Sci.
Conference Abstract:
IMMR | International Meeting on Marine Research 2016.
doi: 10.3389/conf.FMARS.2016.04.00048
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Received:
11 May 2016;
Published Online:
13 Jul 2016.
*
Correspondence:
Dr. Francisco J Aznar, University of Valencia, Cavanilles Institute of Biodiversity and Evolutionary Biology, Paterna, Valencia, 46980, Spain, francisco.aznar@uv.es