Of the interactions between eye fluke parasites and salmonid fishes

In addition to their major biological significance, parasites interest scientists due to their importance in agriculture, aquaculture and medicine. In this thesis I look at local adaptation between salmonid fishes and Diplostomatidae parasites as well as genetic differences in rainbow trout resistance and tolerance against Diplostomum sp. parasite infection. I also study phenotypic and genetic correlations between fish resistance and tolerance and other fitness-related traits to find possible trade-offs. The results are combined with the literature on host-parasite coevolution to gain more understanding on how host-parasite dynamics work and how the health, welfare and productivity of the fish could be further enhanced in captive populations. The results indicate local adaptation of parasites and genetic differences in fish resistance against eye flukes in salmonid fishes. The heritability of resistance was estimated to be of moderate degree (h2 = 0.25–0.35) in farmed rainbow trout. There was genetic variation also in fish tolerance against eye flukes, contradicting the hypothesis that tolerance traits should quickly become fixed. Phenotypic and genetic correlations between parasite resistance, tolerance and other fitness-related traits were estimated to find out possible trade-offs, and also for the purposes of the rainbow trout breeding programme. There was no indication of trade-offs between fish resistance and the other studied traits. Fish with lower resistance tended to grow fast during the first months of their life but over the time, parasite-induced cataracts blinded the fish and growth slowed down. Survival was also reduced among the families having lower resistance and more severe cataracts. Yet, a trade-off between fish performance in the absence of parasites and tolerance emerged when parasite load increased. The fish that had the highest weight and the lowest mortality in the absence of parasites tolerated the parasitism the worst. Resistance and tolerance were not genetically correlated, indicating that the two defence mechanisms are independent from each other. In the arms-race of coevolving host and parasite populations, host resistance and tolerance have different consequences. Resistance favours an increase in parasite infectivity and virulence, whereas tolerance does not cause such selection pressure on parasites. The results of my thesis give new information to improve rainbow trout breeding stock. Resistance and tolerance can both be selected for without compromising productivity.

Grantor dc:publisher

Helsingin yliopisto

Year dc:date.issued

2020

Author dc:creator

• Kuukka-Anttila, Hanna

• ekologia ja evoluutiobiologia

Statement dc:rights

• Julkaisu on tekijänoikeussäännösten alainen. Teosta voi lukea ja tulostaa henkilökohtaista käyttöä varten. Käyttö kaupallisiin tarkoituksiin on kielletty.
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• Publikationen är skyddad av upphovsrätten. Den får läsas och skrivas ut för personligt bruk. Användning i kommersiellt syfte är förbjuden.

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/10138/319384

OAI record oai:identifier

https://helda.helsinki.fi/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Ahelda.helsinki.fi%3A10138%2F319384