A total of 22 fish species have been introduced into the inland waters of Serbia, either intentionally or accidentally. This paper provides a summary of data concerning time and reason of introduction, mode of expansion, degree of acclimatization, impact on native fish and estimated area of recent distribution. Four of the non-native fish species currently occupy more than 51% of Serbian territory while 5 of them occupy between 21-50% of territory. This paper reviews impacts of introduced freshwater fish in Serbia based on collected data.

We present an isolated Milky Way-like simulation in GADGET2 Nbody SPH code. The Galactic disk star formation rate (SFR) surface densities and stellar mass indicative of Solar neighbourhood are used as thresholds to model the distribution of stellar mass in life friendly environments. SFR and stellar component density are calculated averaging the GADGET2 particle properties on a 2D grid mapped on the Galactic plane. The peak values for possibly habitable stellar mass surface density move from 10 to 15 kpc cylindrical galactocentric distance in 10 Gyr simulated time span. At 10 Gyr the simulation results imply the following. Stellar particles which have spent almost all of their life time in habitable friendly conditions reside typically at ∼ 16 kpc from Galactic centre and are ∼ 3 Gyr old. Stellar particles that have spent ≥ 90% of their 4 − 5 Gyr long life time in habitable friendly conditions, are also predominantly found in the outskirts of the Galactic disk. Less then 1% of these particles can be found at a typical Solar system galactocentric distance of 8 − 10 kpc. Our results imply that the evolution of an isolated spiral galaxy is likely to result in galactic civilizations emerging at the outskirts of the galactic disk around stellar hosts younger than the Sun.

Motivated by recent developments impacting our view of Fermi's paradox (absence of extraterrestrials and their manifestations from our past light cone), we suggest a reassessment of the problem itself, as well as of strategies employed by SETI projects so far. The need for such reevaluation is fueled not only by the failure of searches thus far, but also by great advances recently made in astrophysics, astrobiology, computer science and future studies, which have remained largely ignored in SETI practice. As an example of the new approach, we consider the effects of the observed metallicity and temperature gradients in the Milky Way on the spatial distribution of hypothetical advanced extraterrestrial intelligent communities. While, obviously, properties of such communities and their sociological and technological preferences are entirely unknown, we assume that (1) they operate in agreement with the known laws of physics, and (2) that at some point they typically become motivated by a meta-principle embodying the central role of information-processing; a prototype of the latter is the recently suggested Intelligence Principle of Steven J. Dick. There are specific conclusions of practical interest to astrobiological and SETI endeavors to be drawn from coupling of these reasonable assumptions with the astrophysical and astrochemical structure of the spiral disk of our Galaxy. In particular, we suggest that the outer regions of the Galactic disk are most likely locations for advanced SETI targets, and that sophisticated intelligent communities will tend to migrate outward through the Galaxy as their capacities of information-processing increase, for both thermodynamical and astrochemical reasons. However, the outward movement is limited by the decrease in matter density in the outer Milky Way. This can also be regarded as a possible generalization of the Galactic Habitable Zone, concept currently much investigated in astrobiology.

Ljubojević D., Ćirković M., Đorđević V., Puvača N., Trbović D., Vukadinov J., Plavša N. (2013): Fat quality of marketable fresh water fish species in the Republic of Serbia. Czech J. Food Sci., 31: 445-450.The chemical and fatty acid composition were evaluated of commercially important fish species (common carp, silver carp, bighead carp, grass carp, Wels catfish, and zander) which were collected from retail stores in the area of Novi Sad, Republic of Serbia. The amount of protein was the highest in zander (19.27%) and the lowest in grass carp fillets (14.73%). The percentage of fat ranged from 1.8 in zander to 10.07 in common carp. The total cholesterol content was the highest in Chinese carps fillets (approximately 65.38 mg/100 g), and the lowest in Wels catfish (33.14 mg/100 g). SFA were lowest in zander (28.6%). Bighead carp meat contained the highest percentage of PUFA (33.73%) while the lowest percentage was detected in common carp (20.1%). The chemical and fatty acid compositions of fish vary greatly between different species and within the same species. The quality of fish meat in Serbian retail stores is quite good but it should be improved by using feed mixtures on fish ponds.

Can astrophysics explain Fermi's paradox or the "Great Silence" problem? If available, such explanation would be advantageous over most of those suggested in literature which rely on unverifiable cultural and/or sociological assumptions. We suggest, instead, a general astrobiological paradigm which might offer a physical and empirically testable paradox resolution. Based on the idea of James Annis, we develop a model of an astrobiological phase transition of the Milky Way, based on the concept of the global regulation mechanism(s). The dominant regulation mechanisms, arguably, are gamma-ray bursts, whose properties and cosmological evolution are becoming well-understood. Secular evolution of regulation mechanisms leads to the brief epoch of phase transition: from an essentially dead place, with pockets of low-complexity life restricted to planetary surfaces, it will, on a short (Fermi-Hart) timescale, become filled with high-complexity life. An observation selection effect explains why we are not, in spite of the very small prior probability, to be surprised at being located in that brief phase of disequilibrium. In addition, we show that, although the phase-transition model may explain the "Great Silence", it is not supportive of the "contact pessimist" position. To the contrary, the phase-transition model offers a rational motivation for continuation and extension of our present-day Search for ExtraTerrestrial Intelligence (SETI) endeavours. Some of the unequivocal and testable predictions of our model include the decrease of extinction risk in the history of terrestrial life, the absence of any traces of Galactic societies significantly older than human society, complete lack of any extragalactic intelligent signals or phenomena, and the presence of ubiquitous low-complexity life in the Milky Way.

B N B  M M.  Ć  In a recent paper in this journal, Ken Olum attempts to refute the doomsday argument by appealing to the self-indication assumption (SIA) that your very existence gives you reason to think that there are many observers. Unlike earlier users of this strategy, Olum tries to counter objections that have been made against (SIA). We argue that his defence of (SIA) is unsuccessful. This does not, however, mean that one has to accept the doomsday argument (or the other counter-intuitive results that flow from related thought-experiments). A developed theory of observation selection effects shows why the doomsday argument is inconclusive, and how one can consistently reject both it and (SIA).

We critically investigate some evolutionary aspects of the famous Drake equation, which is usually presented as the central guide for the research on extraterrestrial intelligence. It is shown that the Drake equation tacitly relies on unverifiable and possibly false assumptions on both the physico-chemical history of our Galaxy and the properties of advanced intelligent communities. The importance of recent results of Lineweaver on chemical build-up of inhabitable planets for SETI is emphasized. Two important evolutionary effects are briefly discussed and the resolution of the difficulties within the context of the phasetransition astrobiological models sketched.

We review Fermi's paradox (or the "Great Silence" problem), not only arguably the oldest and crucial problem for the Search for ExtraTerrestrial Intelligence (SETI), but also a conundrum of profound scientific, philosophical and cultural importance. By a simple analysis of observation selection effects, the correct resolution of Fermi's paradox is certain to tell us something about the future of humanity. Already more than three quarters of century old puzzle -and a quarter of century since the last major review paper in the field by G. David Brin -has generated many ingenious discussions and hypotheses. We analyze the often tacit methodological assumptions built in various answers to this puzzle and attempt a new classification of the numerous solutions proposed in an already huge literature on the subject. Finally, we consider the ramifications of various classes of hypotheses for the practical SETI projects. Somewhat paradoxically, it seems that the class of (neo)catastrophic hypotheses gives, on the balance, the strongest justification to optimism regarding our current and near-future SETI efforts.