NATURA SLOVENIAE 25(1): 47-48 Prejeto / Received: 17. 11. 2022 
FIELD NOTE Sprejeto / Accepted: 15. 5. 2023 
 
DOI: 10.14720/ns.25.1.47-48 
 Biotehniška fakulteta Univerze v Ljubljani in Nacionalni inštitut za biologijo, Ljubljana, 2023 
The first record of the Monkey 
goby Neogobius fluviatilis 
(Pallas, 1814) (Pisces: 
Gobiidae) in Slovenia 
 
Prva opisana najdba rečnega glavoča 
Neogobius fluviatil is (Pallas, 1814) 
(Pisces: Gobiidae) v Sloveniji 
 
Luka MRZELJ, Fisheries research institute of 
Slovenia, Spodnje Gameljne 61a, SI-1211 
Ljubljana-Šmartno, Slovenia; E-mail: 
luka.mrzelj@zzrs.si 
 
The first confirmed presence of the Monkey goby 
fish species, Neogobius fluviatilis (Pallas, 1814) in 
Slovenia has been recorded in August 2021. During 
regular Fisheries Research Institute of Slovenia 
surveys, nine individuals were caught in Ledava 
River within Murska šuma near the town Pince  
(Lat: 46.500556, Lon: 16.531944). Ledava River is 
lowland watercourse with minimal discharge of 
0,145 m3/s recorded at Čentiba station in 2003 
(ARSO 2022). 
 
The Monkey goby species can be distinguished from 
related species by the length of the first branched 
ray in the secondary dorsal fin (Kotelat & Freyhoff 
2007). The first branched ray is twice as long as the 
penultimate ray. In 2022, specimens from Ledava 
River were also genetically confirmed at the Chair of 
Genetics, Animal Biotechnology and Immunology at 
Biotechnical Faculty, University of Ljubljana (Sušnik 
S., pers. comm.). In a 100 m long river transect with 
an average water depth of 0.7 m and wetted width 
of 5 m, the specimens were caught using the 
electrofishing backpack sampling method. 
Specimens measured from 39 to 65 mm in total 
length, while it is reported that Monkey goby can 
reach from 100 mm to 200 mm in length (Kotelat & 
Freyhoff 2007; Placha et al. 2010; Grabowska 2011; 
Staszny et al. 2022). In the Ledava River, Monkey 
gobies were found in runs, hidden under stones and 
rocks, which represented the dominant substrate 
fraction (60%) of the riverbed. This is rather 
surprising, as the species is considered to spend 
most of its time on sandy substrates (Kotelat & 
Freyhoff 2007). However, the recent book on 
invasive animal species in Hungary suggest that 
monkey gobies actually prefer stony bottoms, and 
their presence on sandy bottoms is a consequence 
of competition with sister species (Staszny et al. 
2022). Monkey goby lives up to 5 years and it 
spawns for the first time in the second year 
(Smirnov 1986; Kotelat & Freyhoff 2007). Females 
can spawn a few times per season. Adhesive eggs 
are deposited on stones, shells and/or aquatic 
plants. During the spawning season, from April to 
July, locally until September, males have a 
completely black body with yellow fin-margins 
(Kotelat & Freyhoff 2007). The male guards the nest 
aggressively and takes care of the offspring until it 
hatches (Pinchuk et al. 2003). Gobies are 
generalists, as well as omnivores and mostly feed 
on benthic invertebrates (Kotelat & Freyhoff 2007). 
Larger specimens can become piscivorous and feed 
on smaller fish or fish fry. 
 
 
Figure 1. Monkey goby (Neogobius fluviatilis) from Ledava River (photo: L. Mrzelj). 
Slika 1. Rečni glavoč (Neogobius fluviatilis) iz reke Ledave (foto: L. Mrzelj). 
 
48 Luka MRZELJ: The first record of the Monkey goby Neogobius fluviatilis (Pallas, 1841) in Slovenia / FIELD NOTE 
NATURA SLOVENIAE 25(1): 47-48 
The Monkey goby belongs to the Ponto-Caspian 
goby group. The initial distribution area of the 
species is Eastern Europe (Povž 2016); the Black, 
Azov, Marmara Sea Basins and the Caspian Lake. 
These goby species have already been recorded in 
the 90s of the 20th Century spreading across 
Northern and Western Europe (Povž 2016). The 
increased expansion range of the species is strongly 
attributed to a large human contribution. The 
Ponto-Caspian gobies expansions are accelerated 
due to watercourse transportation industry and 
habitat degradation. Gobies can spread over long 
distances in waterbodies via ship transportation 
(Anheit et al. 1998). Consequently, some authors 
describe their range expansion as invasive (Kotelat 
& Freyhoff 2007). In 1970, the Monkey goby was 
introduced into the Lake Balaton in Hungary 
(Kotelat & Freyhoff 2007). In 2006, Veenvliet and 
Veenvliet described that the species has dispersed 
along the Danube River, reaching Croatia. In 2022, 
the species was recorded in Drava and Mura River 
systems (Rauch 2022) from where it could 
successfully reach lower stretches of the Ledava 
River. Until today, the presence of two Ponto-
Caspian goby species was confirmed in Slovenia; 
the Monkey goby in Ledava River in 2021 and the 
Bighead goby in Sava River near Obrežje in 2016 
(Povž 2016). »Monkey goby« occurrence for Sava 
River including tributaries Sora, Ljubljanica, Mirna, 
Krka, Kolpa and Savinja (Simonović et al. 2015) 
cannot be considered as reliable, since there is no 
reference or field data, which could confirm the 
recorded find. Therefore, Ledava River can be 
considered as the first recorded find of Monkey 
gobies in Slovenia. Considering Ponto-Caspian 
gobies expansion trends, we can expect an increase 
of species finds and records of more specimens in 
Slovenia in the near future. 
 
Acknowledgements 
 
I would like to thank dr. Simona Sušnik Bajec for the 
genetic identification of the species and to all collegues who 
helped during this survey. 
 
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