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Sirvi Autor "Gross, Riho (advisor)" järgi

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  • Pisipilt
    Kirje
    Analysis of molecular genetic and life-history traits in Eurasian perch (Perca fluviatilis L.)
    (Eesti Maaülikool, 2016) Pukk, Lilian; Vasemägi, Anti (advisor); Gross, Riho (advisor); Paaver, Tiit (advisor); Volckaert, Filip (opponent)
    Fishes provide food and livelihood for hundreds of millions of people around the world and currently fish consumption is higher than ever before. As a consequence, the threats of over-exploitation, illegal fishing and fish trade are very high. Because biologically insensible management actions or lack of necessary regulations may lead to population collapse, better understanding of genetic population structure and fisheries-induced changes in life-history traits is essential for conservation of local fish populations. Thus, the main goals of this thesis were to generate novel genomic resources, characterize population genetic structure, and study the consequences of overfishing of Eurasian perch populations and its potential causes to various life-history traits in Estonia. The over-exploitation of Eurasian perch population had strong influence on size- and age-distribution, juvenile growth rate and age of sexual maturation in males. Development of novel low-cost genome complexity reduction protocol enabled to identify large number of single nucleotide polymorphisms and microsatellite markers. Based on observed genetic structuring between two commercially most important perch fishery locations in Estonia (Väinameri Sea region and Lake Peipus), new microsatellite markers successfully revealed the genetic origin of perch, which can be used to fight against illegal fishing and fish trade. The population genetic framework described within this thesis represents a small but important milestone towards developing biologically sound conservation and management strategies for Eurasian perch.
  • Pisipilt
    Kirje
    Invasive non-indigenous crayfish species as a threat to the noble crayfish (Astacus astacus L.) populations in Estonia
    (Eesti Maaülikool, 2018) Kaldre, Katrin; Paaver, Tiit (advisor); Gross, Riho (advisor); Füreder, Leopold (opponent)
    Once abundant, indigenous noble crayfish stocks in Europe have suffered from a long-term population decline due to the spread of North-American crayfish species. They are latent carriers of the crayfish plague agent Aphanomyces astaci, which is lethal to all European native crayfish species. Until 2008, Estonia was one of the last countries where alien crayfish species had not been recorded in the wild. Presently, two potential plague carriers – signal and spiny cheek crayfish - are present in Estonian rivers, and the marbled crayfish is available in the Estonian aquarium trade. The objectives of this thesis were: (i) to give an overview of the status and distribution of signal crayfish and its possible role in a series of crayfish plague outbreaks in the noble crayfish populations of Estonia; (ii) to estimate survival of the marbled crayfish in Estonian winter conditions and the effect of different feeds on survival, growth, reproduction, behaviour and carapace colouration; (iii) to develop a new set of microsatellite markers for the noble crayfish that also cross-amplify in the potentially invasive narrow-clawed crayfish. Since 2008, the signal crayfish has been recorded at four sites in Estonia, and has caused the extinction of noble crayfish populations at least at two sites. The dispersed pattern of the signal crayfish distribution indicates that these populations are the result of illegal human-assisted introductions. Crayfish plague outbreaks in noble crayfish populations are caused by different A. astaci genotype groups – A, B and E. This indicates that signal crayfish, or possibly other alien crayfish species, may have spread the crayfish plague. This study showed that marbled crayfish can survive in Estonian winter conditions and successfully reproduce later on. Different levels of astaxanthine and protein in feed have a significant effect on carapace colouration, growth rate and mortality of the marbled crayfish. The marbled crayfish has a good adaptability to different environmental conditions, reproduces parthenogenetically, and their spread to the natural environment must be strictly prevented. Using next generation sequencing technology, a set of 48 tetranucleotide repeat microsatellite markers for the noble crayfish were developed that partially cross-amplify in the narrow-clawed crayfish, and can be used for the detection of possible hybrids between these sister species with largely overlapping distribution areas.