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This study gives an overview of status and distribution of signal crayfish (Pacifastacus leniusculus), the first NICS in Estonia and its influence on native noble crayfish (Astacus astacus) populations. The first specimen of signal crayfish was caught during the monitoring of noble crayfish in North Estonia in 2008. The signal crayfish has since been found in three additional sites. Test fishing has indicated that the abundance of signal crayfish has been fluctuating between years and among localities. It has had strong negative impact on abundance of one noble crayfish population. The disconnected distribution of signal crayfish strongly suggests that these populations are the result of human-assisted introductions. Real-time PCR analyses proved that signal crayfish carry the causative agent of the crayfish plague, an oomycete Aphanomyces astaci, thus contributing to its spread. Mortalities in noble crayfish populations had been caused by A. astaci strains from A, B and E genotype group.

We assessed feeding of planktivorous fish larvae on ciliate protozooplankton in shallow eutrophic Lake Vortsjarv, Estonia to determine whether ciliates are an important part of larval fish diet. We collected larvae of the most common fish species and examined their gut contents by gut segmentation and epifluorescence microscopy. Ciliates were present in the gut of all fish larvae. Gut segmentation analysis showed clear differences in food composition between gut quarters. The hard-bodied food items were quite evenly distributed in the gut, but the soft-bodied ciliates and rotifers were present only in the first gut quarters. Neglecting differences in prey digestion rate leads to underestimation of diet amount and composition and, especially, to underestimation of the role of protists in food. In Vortsjarv, ciliates account for ∼ 60% of the total carbon biomass consumed by fish larvae. The food requirement of fish larvae during first feeding stages (May-Jun) would not be met without consumption of ciliates.

The epidermal tissue of fish is often the primary barrier, to pathogens in the environment (Singh and Mittal 1990, Iger et al. 1994, Buchmann et al. 2004, Rakers et al. 2010, Ottesen et al. 2010). The cell-mediated innate mechanisms of epidermal tissues include specialized cells such as macrophages, granulocytes, natural killer cells, and also physical barriers such as mucous layers and skin epithelial tissue lines (Jones 2001, Aoki et al. 2008). The epidermal club cells of many fishes in the superorder Ostariophysi have evolved primarily as part of the immune system (Chivers et al. 2007, Halbgewachs et al. 2009, Ferrari et al. 2010) but their functional mechanisms, with non-specific and/or specific immunity, have not been explored in detail. The evolution of club cells of ostariophysan fish remains enigmatic and controversial as it has been historically linked to chemical alarm signalling (von Frisch 1941, Smith1992, James et al. 2009). However, Carreau-Green et al. (2008) suggested that club cells do not have an alarm function in fathead minnow, Pimephales promelas Rafinesque, 1820. Such evidence would support the possibility that club cells of fishes may be maintained by natACTA ICHTHYOLOGICA ET PISCATORIA (2011) 41 (3): 185–192 DOI: 10.3750/AIP2011.41.3.06

Noble crayfish (Astacus astacus) is listed as vulnerable by the IUCN Red List of Threatened Species in Europe. However, very little is known about genetic diversity and structuring of noble crayfish populations, mainly because of the lack of informative genetic markers. We describe the isolation and characterization of the first microsatellite markers for this species, which were obtained by screening 4,000 recombinant clones. Eight loci revealed polymorphisms in a panel of 172 individuals from seven populations in Northern Europe. Number of alleles per locus ranged from two to 10 (average 4.4) and heterozygosity levels among populations varied from 0 to 0.80 for H o and from 0 to 0.72 for H e.

Patterns of genetic diversity and differentiation among five wild and four hatchery populations of Atlantic salmon in the Baltic Sea were assessed based on eight assumedly neutral microsatellite loci and six gene-associated markers, including four expressed sequence tag (EST) linked and two major histocompatibility complex (MHC) linked tandem repeat markers (micro- and mini-satellites). The coalescent simulations based on the method of Beaumont and Nichols (1996, Proc. R. Soc. Lond. Ser. B – Biol. Sci., 263, 1619–1626) indicated that two loci (MHCIIα and Ssa171, with the lowest and highest overall FST estimates, respectively) exhibited significant departures (P

Three all-female strains of large rainbow trout imported to Estonia (Danish, Finnish and Donaldson strain) were evaluated in a communal rearing experiment in tanks. The fish had been reared on different fish farms before the experiment started and they had an initial weight of 400–500 g. There were no significant genetic differences between the investigated strains on the basis of three allozyme loci. The total weight gain of the strains during the trial was similar but differences were revealed between seasons. The growth rate of the Finnish trout was high during the first autumn but decreased during the second summer of the trial, probably due to infestation by eye fluke Diplostomum sp. The strains differed in the percentage of immature fish and in the level of gonad development at the age of 2.5–3 years. The Donaldson strain had the highest number of immature fish of the studied strains. Mature females of the Finnish strain had the smallest gonads but also the lowest percentage of immature fish. The level of maturation was the main factor determining the quality – slaughter yield and flesh color.

The genetic structure and isolation pattern of the Atlantic salmon (Salmo salar) throughout its range in the Baltic Sea were examined as a starting point for a conservation strategy for the species in this area. The allozyme variation in seven polymorphic loci was studied in 5125 salmon from 24 rivers in four countries. A clear dichotomy was observed between stock groups from southeastern (Russia, Estonia, Latvia, southern Sweden) and northwestern (northern Finland, northern Sweden) drainage regions, corresponding to the postglacial colonisation of the Baltic Sea by two phylogeographic lineages, one from the east (the Ice Lake lineage) and one from the west (the Atlantic lineage). The geographical and genetic distances between stocks fit the one-dimensional "isolation-by-distance" model (p < 0.001). The estimated gene flow ranged from 0 to10 migrants per generation. The total diversity of hatchery stocks was 72% of that of the wild stocks. Genetically similar stock groups, phylogeographic lineages, and drainage regions are recommended for use as genetic management units in addition to stock level.

Isoenzyme analysis is a fast and inexpensive method for taxonomic and population genetic analyses. Variation of eight enzymes and two non-specific blood proteins among five species of eagles in genus Aquila was analysed with the aim of detecting species-specific markers and intraspecies variation for population genetic studies. However, no isoenzyme variability was detected. We conclude that isoenzyme analysis of blood samples has limited value for taxonomic, population and hybridization studies among eagles.

The founder event in a recently recolonized salmon population in the Baltic Sea (Gulf of Finland) was investigated. To identify the origin of the founders, four wild populations and two hatchery stocks were analysed using six microsatellite loci. The results of assignment tests and factorial correspondence analysis suggest that the initial recolonizers of the river Selja originated from the geographically nearest (7 km) wild population (river Kunda) but as the result of stocking activities, interbreeding between recolonizers and hatchery individuals has occurred in subsequent years. Although the hatchery releases are outnumbering the wild salmon recruitment in the Baltic Sea at present, our results suggest that the native populations may still have an important role in colonization processes of the former salmon rivers.

Sixty-four samples from 46 salmon populations totalling 2369 specimens were used for polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis of the mitochondrial ND1 region. The final analyses included 3095 specimens from 60 populations in Northern Europe. A subsample was analysed by RFLP of ND3/4/5/6. Representative RFLP haplotypes from different parts of the distribution area were sequenced and the phylogeny of European haplotypes and their relations to the North American lineage was described. The four common European haplotypes derive from the ancestral ND1-BBBA (rooting the European clade to the North American) by one-step substitutions: AAAAAABABBBABBBB. The Swedish west-coast populations differ from the geographically close southern Baltic, indicating absence of inward and limited outward gene flow through the Danish straits during the last 8000 years. Within the Baltic Sea, only three ND1 haplotypes were detected and there was no variation for ND3/4/5/6. In the whole southern Baltic and in lakes Vänern, Ladoga and Onega the haplotype AABA dominated. Proposed postglacial colonization routes to the Baltic Sea are discussed in relation to the haplotype distribution pattern.

Description: Noble crayfish (Astacus astacus L.) is the most common and the most highly appreciated freshwater crayfish species in Europe. Once abundant, it is now listed as vulnerable by the IUCN Red List of Threatened Species, and there is increased interest in the aquaculture of this species for stocking and consumption purposes. Allozyme studies revealed little variation in A. astacus and stressed the need for the development of more informative microsatellite markers. We report here the isolation and characterization of 11 polymorphic microsatellite markers that, together with eight loci from our previous study, allow us to assess and monitor genetic variation in natural and farmed populations of A. astacus.