**1. Introduction**

Considering the prospects associated with the appearance of invasive species of animals at a new continent, some of the possible consequences are usually missed. It is often expected that the distribution and naturalization of invasive alien species can be controlled. However, this cannot always be possible since in open biosystems (natural and anthropogenic), in addition to other human activities leading to the spread of invasive alien species, the influence of changing climatic conditions, as the most global consequence of human activity takes place. However, the influence of all these negative factors (moving species between countries, uncontrolled release, wrong usage as agents of bimethod, accidental introduction, hunting, disbalancing of local ecosystems, etc.) as a whole can lead to the suppression of native animal species [1] and the emergence of species new to the local environment [2–7]. These factors can actively displace not only representatives of the ichthyofauna, but also batrachofauna [8]. Therefore, the main questions that we must ask ourselves are as follows: (1) What is the preferable (optimal) environment for an invasive species and in which regions naturalization and appearance of the species is possible; (2) what consequences of

**Citation:** Nekrasova, O.; Tytar, V.; Pupins, M.; Ceir ˇ ans, A.; Marushchak, ¯ O.; Skute, A. A GIS Modeling Study of the Distribution of Viviparous Invasive Alien Fish Species in Eastern Europe in Terms of Global Climate Change, as Exemplified by *Poecilia reticulata* Peters, 1859 and *Gambusia holbrooki* Girarg, 1859. *Diversity* **2021**, *13*, 385. https://doi.org/10.3390/ d13080385

Academic Editor: Michael Wink

Received: 8 July 2021 Accepted: 11 August 2021 Published: 17 August 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

this appearance could be for native species and for the environment in general; (3) where do invasive species come from and what are the possible ways to avoid this; 4) what can influence invasive species as a limiting factor (besides climate conditions)—predators, parasites, illnesses. Of great interest is the appearance (or prospects of appearance) in temperate latitudes of thermophilic poikilothermic animals with their own strategy of viviparity, which gives them an opportunity to reproduce even in non-optimal conditions (for example, in human transformed territories). They also thrive and reproduce in both fresh and brackish water. Representatives of the genera *Gambusia* [9] and *Poecilia* [10] came to Europe as agents of a biological method for controlling the malaria mosquitos at the beginning of 20th century (they were released into the reservoirs of Western Europe). In addition, previously they also were bred in quantities in aquarium farms as aquarium fish. Two closely related species of this genus were introduced in Europe for the above mentioned purpose: *Gambusia affinis* (Baird and Girard, 1853) and *Gambusia holbrooki* (Girard, 1859), but the latter species is the most widespread and occurs in Ukraine.

*G. holbrooki* is a viviparous freshwater fish species (Poeciliidae family) originating from southern areas of North America. The species demonstrates great plasticity in the preference of comfortable water temperatures, thriving at +31–+38 ◦C, but being able to survive beyond these values [10]. This planktivorous species was used as an agent of biological control and was introduced in 1921 to the Iberian Peninsula for the first time to combat malaria. Later on the fish expanded an area of its invasion to Italy in 1922 and other Mediterranean countries, like Greece, Croatia, Spain etc. [11]. Currently this invasive alien species is well known in about 50 countries worldwide [9,12]. Besides being used to control mosquito populations, this species is known to have negative effects on local populations of aboriginal amphibian and fish species [13,14], which necessitates the study of its potential distribution, in terms of global climate change of particular importance in order to preserve local biodiversity.

*P. reticulata* is another viviparous freshwater fish species from North America that became invasive in Europe over recent decades. The wild form of the guppy was introduced to Europe in the 19th century. It was also used to fight malaria; thus it was introduced to many places. Being a popular polymorphic aquarium species, and due to their better resistance to colder water (up to +12 ◦C), guppies became invasive as a result of many accidental releases from aquaria [10,15]. Their ability to store sperm for months made it possible even for a one single gravid female to start a new population [16]. A wild population of guppies permanently lives in the Moskva river in the area of warm water discharge in Lyubertsy (Kuryanovsk drains) and in other places of this river [17,18]. Recently, in the Upper Volga basin, numerous self-reproducing populations of guppies have been noted in the regions of large cities (Tver, Yaroslavl, Rybinsk) in the areas of heated water discharge, as well as in settling ponds in facilities for the purification of domestic wastewater [19,20]. In their homeland, the island guppy populations live in brackish and seawater; they are bright in color and large in size. Optimal conditions for guppies include: clean water with a temperature of about +24 ◦C (the range being +16–+30 ◦C), the presence of zones with vegetation and free for swimming, a varied diet with a substantial proportion of live food. There are no data on the biology of this species from the Moskva river. It is known that there it reaches a high number and can be caught with a net in large quantities. For water bodies of the Upper Volga, there is an indication that it does not occur in water bodies with a temperature under +17 ◦C [20].

Such assumptions about appearance and distribution of these species in Eastern Europe are most relevant in connection with their potential usage as agents of biological control against the emergence of new carriers of various diseases—blood-sucking insects [21]. Therefore, the purpose of our work was to study both climatic indicators of environmental optima for these invasive alien species, and possible spread of these species over Eastern Europe in space and time.
