Method of installation into a natural water body of material of stocking of crayfish of the subfamily Astacinae Latreille, 1802, obtained in artificial conditiohs

Results of experimental and analytical researches on restoration of stocks of crayfish of subfamily Astacinae Latreille, 1802 in water body of the Forest zone of the European part of Russia by introduction of larvae of the early stages received in artificial conditions are presented. Researches were conducted in 1995–2020 under programs of Rosrybhoz, Tver’rybhoz, the Russian Academy of agricultural sciences and the Ministry of the Science and Higher education of the Russian Federation. To restore the stocks of crayfish in the Tver Region, larvae of early age stages obtained under artificial conditions were placed in frame devices installed along the shore of the water body, covered with a fine-mesh netting with a small slit left near their bottom. The differences in the environment in the growing pond (fish farm pond) and in the larval introduction pond (Puiga River) were minimal. In devices filled with aquatic vegetation enriched with food organisms, the larvae had the opportunity to adapt to the new environment, find food organisms, and gradually get out through the slit into the water body. A survey of the results of this method of introducing of stocking material, carried out after 1.5–2 months, made it possible to establish the absence of larvae in the devices, and to find in the river backwater downstream a lot of larvae that grew up to the 6th age stage with a body length of 2 and more centimeters. The number of larvae in the backwater was established by calculation based on the results of an approximate calculation of their number per 165 copies/m² of the river bottom inhabited by crustaceans, the settlement area was 15.8 m². The number of found grown-up larvae allowed us to estimate approximately the survival rate of the universal planting material of cancer at least 36%.

MORPHOLOGICAL AND PHYSIOLOGICAL CHARACTERISTICS OF JUVENILE STURGEON REARED IN HATCHERIES OF THE ASTRAKHAN REGION

The article focuses on the study of changeability of morphological and physiological characteristics of 850 specimens of beluga ( Huso huso ) and sturgeon ( Acipenser gueldenstaedtii ) juveniles obtained at the Ikryaninskiy and Bertyulskiy sturgeon hatcheries in the Astrakhan region. There was determined weight of the body, heart, liver and spleen, as well as the relative mass of these organs - cardiosomatic, hepatosomatic indices and index of a spleen. Sturgeon juveniles were studied within 47-127 days, beluga juveniles within 40-116 days. Certain tendency was noted: cardiosomatic index decreased with aging in both sturgeon and beluga, i.e. the relative weight of the heart in ontogenesis changes inversely to the body weight, which corresponds to literature data. Comparison of the dynamics of the liver relative weight in sturgeon and beluga juveniles showed that it coincides at two segments: maximum raise to 50-60ths day from the birth and a gradual decrease in older juveniles. The value of spleen index in juveniles of both types rose with aging. It was found in the course of the study that the size of internal organs could change, getting smaller under unfavorable factors, in particular, when juveniles suffer from the lack of feeds. In such circumstances the dynamics of developing main internal organs drastically slows down, which reflects on physiological adequacy (quality) of juveniles. Thus, morphological and physiological indicators characterizing the degree of the vitals development can be used not only for characterizing species differences of the investigated group of fish at all stages of ontogenesis, but as important factor for assessing conditions of Russian sturgeons juvenile breeding and the degree of morphological and physiological maturity of the juveniles before releasing into the natural water body.

First record of Craspedacusta sowerbii Lankester, 1880 (Hydrozoa, Limnomedusae) in a natural freshwater lagoon of Uruguay, with notes on polyp stage in captivity

The freshwater cnidarian Craspedacusta sowerbii Lankester 1880, has invaded lakes and ponds as well as artificial water bodies throughout the world. The first record in Uruguay corresponding to the jellyfish was made in 1961 in two artificial fountains, with no mention of the polyp form. Although local reports of other related polyp species have been made, information on the benthic form of C. sowerbii is lacking. Here we report the finding of live frustules, solitary individuals, medusae and colonies from a natural lagoon in August 2010, allowing us to observe the morphology and behavior of the polyp stage in captivity. In addition, molecular identification and remarks on the potencial path of introduction are presented. This is the first record in Uruguay of both polyp and medusa stages of C. sowerbii in a natural water body, Del Medio Lagoon (Dpto. de Florida), Uruguay.

Checklist of benthic macroinvertebrates of the Lago Pratignano (northern Apennines, Italy): an extremely rich ecosystem

A checklist of the macroinvertebrates fauna of the Lago Pratignano is presented here. The Lago Pratignano is a small, natural water body of the high (1,307 m above sea level) Northern Apennines, Italy. It represents an important site for the conservation of endangered flora and amphibians, and its importance for the conservation of the macroinvertebrate fauna is highlighted. The 82 taxa recorded make it an extremely rich habitat. The most represented group was Diptera, with 31 taxa, followed by Coleoptera, with nine, and Oligochaeta and Arachnida, each with eight taxa. Other groups are present in lower numbers. Despite the scant attention to theP study of the macroinvertebrates of small lentic habitats in the Northern Apennines, their importance for the conservation of the invertebrate fauna and the high contribution they give to the biodiversity is highlighted here.

CHARACTERIZATION OF THE IRREGULARITY OF A TERRAIN USING FRACTAL DIMENSION OF LAKES' BOUNDARIES

Even though many objects and phenomena of importance in geophysics have been shown to have fractal character, there are still many of them which show self-similar character and yet to be studied. The objective of the present work is to demonstrate that the fractal dimension of the boundary of a natural water body can be used to shed light on irregularity as well as other properties of a region. Owing to easy availability of satellite images and image processing softwares, this turns out to be a handy tool. In this study, we have analyzed several lakes in India mostly around the Western Ghats region. We find that the fractal dimension of their boundaries for the length scales between around 40 m to 2 km, in general, has broad variation from 1.2 to 1.6. But when they are grouped into three categories, viz., lakes along the ridge of Western Ghats, lakes in the planes and lakes in the mountain region, we find the first two groups to have a narrower distribution of dimensions.