Case of highly prevalent papilloma-like skin lesions in whitespotted char (Salvelinus leucomaenis) in Kamchatka (Russia).

In October 2014, a case of mass skin lesions was reported in whitespotted char (Salvelinus leucomaenis) caught in the Nalycheva River on the Kamchatka peninsula (Russia). The proportion of affected fish was approximately 50% of the catch. Lesions of varying severity were noted from small tubercles to large single and confluent formations and ulcers. Papilloma-like growths were found in the epidermal layer of the skin of the affected fish. Histopathological alterations included the following: submerged growth of epithelial cells, infiltration of inflammatory cells, oedema of scale pockets, resorption of scales, haemorrhages, local necrosis and an increased number of mucous cells. In the dermal layer of the skin, haemorrhages and extensive necrosis were recorded. Inflammation, necrosis and destruction of myocytes were found in the underlying musculature. This is the first documented case of papilloma-like skin lesions found in salmonids in Kamchatka. The affected whitespotted char were deemed unsuitable as a food product due to their unsatisfactory appearance and impermissible levels of bacterial contamination of the muscles.

Description of a metacercaria of a zoogonid trematode Steganoderma cf. eamiqtrema Blend and Racz, 2020 (Microphalloidea: Zoogonidae), with notes on the phylogenetic position of the genus Steganoderma Stafford, 1904, and resurrection of the subfamily Lecithostaphylinae Odhner, 1911.

Metacercariae of the zoogonid trematode Steganoderma cf. eamiqtrema ex crab Chionoecetes bairdi caught in the Sea of Okhotsk were described using morphological and molecular-genetic (ITS2 region, 28S rRNA and nd1 genes) data. These are the first molecular-genetic data for the genus Steganoderma. The studied trematodes differed from S. eamiqtrema in having a much larger body size. The phylogenetic analysis based on the 28S rRNA gene supported neither the current taxonomic hypothesis that Steganoderma belongs to the subfamily Lepidophyllinae nor the earlier views that the Steganodermatinae and the Lecithostaphylinae are synonymous. The topology of the phylogenetic tree shows that the Steganodermatinae and the Lecithostaphylinae are independent subfamilies. However, morphological differences between them are obscure. Until morphological evidence for the Steganodermatinae is found, we propose to distinguish the subfamily Lepidophyllinae sensu stricto with the genera Lepidophyllus and Urinatrema, and the subfamily Lecithostaphylinae sensu lato uniting all the other former lepidophyllines. Thus, for now, we propose to consider the Steganodermatinae as a conditional synonym for Lecithostaphylinae sensu lato.

Sensitivity analysis of consumption cycles.

We study the special case of a nonlinear stochastic consumption model taking the form of a 2-dimensional, non-invertible map with an additive stochastic component. Applying the concept of the stochastic sensitivity function and the related technique of confidence domains, we establish the conditions under which the system's complex consumption attractor is likely to become observable. It is shown that the level of noise intensities beyond which the complex consumption attractor is likely to be observed depends on the weight given to past consumption in an individual's preference adjustment.

Stochastic sensitivity technique in a persistence analysis of randomly forced population systems with multiple trophic levels.

Motivated by important ecological applications we study how noise can reduce a number of trophic levels in hierarchically related multidimensional population systems. A nonlinear model with three trophic levels under the influence of external stochastic forcing is considered as a basic conceptual example. We analyze a probabilistic mechanism of noise-induced extinction of separate populations in this "prey-predator-top predator" system. We propose a new general mathematical approach for the estimation of the proximity of equilibrium regimes of this stochastic model to hazardous borders where abrupt changes in dynamics of ecological systems can occur. Our method is based on the stochastic sensitivity function technique and visualization method of confidence domains. Constructive abilities of this mathematical approach are demonstrated in the analysis of different scenaria of noise-induced reducing of the number of trophic levels.

Stochastic bifurcations caused by multiplicative noise in systems with hard excitement of auto-oscillations.

We study a stochastic dynamics of systems with hard excitement of auto-oscillations possessing a bistability mode with coexistence of the stable equilibrium and limit cycle. A principal difference in the results of the impact of additive and parametric random disturbances is shown. For the stochastic van der Pol oscillator with increasing parametric noise, qualitative transformations of the probability density function form "crater"-"peak+crater"-"peak" are demonstrated by numerical simulation. An analytical investigation of such P bifurcations is carried out for the stochastic Hopf-like model with hard excitement of self-oscillations. A detailed parametric description of the response of this model on the additive and multiplicative noise and corresponding stochastic bifurcations are presented and discussed.