Gordeev et al.: The first data on the diet and reproduction of Eumicrotremus fedorovi 37 
Oocyte diameter (um 
Oocyte stage 
Figure 3 
Box plot of the relationship between oocyte diameter and 
histological stages of maturity for Fedorov’s lumpsucker 
(Eumicrotremus fedorovi) caught during 19-25 March 
2017 around Simushir Island. The stages of oocyte devel- 
opment are primary growth (1), early developing (2), devel- 
oping (3), fully vitellogenic (4), and maturing (5). The upper 
and lower parts of each box represent the first and third 
quartiles (the 25" and 75th percentiles), and the horizon- 
tal line is the median. The error bars indicate 1.5 times the 
interquartile range, and the black circles represent values 
outside this range. 
eurybathic species, as has been reported previously for 
all lumpsucker species (Chuchukalo, 2006; Gordeev and 
Sokolov, 2020). All 3 fish species found in the stomach 
contents of Fedorov’s lumpsucker—the walleye pollock, 
northern lampfish, and northern smoothtongue—are 
quite common in the area of and use the shelf of the Kuril 
Islands as breeding grounds. It is interesting that we did 
not find cumaceans or isopods in the stomach contents 
because they usually follow gammarids on the shelf 
(Neiman, 1988). Perhaps it is due to the feeding selectiv- 
ity or the mosaic of bottom fauna. 
A detailed analysis of food items allowed us to compare 
our results with the available data on the diet of congeners 
of the Fedorov’s lumpsucker. According to Roshchin (2006), 
who studied the diet of Atlantic spiny lumpsucker in the 
Barents Sea, pelagic crustaceans of the family Hyperiidae, 
that is Themisto abyssorum and T. libellula, form the bulk 
of the food bolus of the Atlantic spiny lumpsucker. Benthic 
gammarids of the family Lysianassidae and a high Arctic 
species, Gammarus wilkitzkii, were also found. Northern 
shrimp (Pandalus borealis); a euphausiid, Thysanoessa 
inermis; and polychaetes of the genus Nereis were found 
in only a few of the examined lumpsucker. Berge and 
Nahrgang (2013) stated that there was a similar pattern 
of Atlantic spiny lumpsucker feeding on Themisto libellula 
in the environs of Spitzbergen, an island in the Svalbard 
archipelago in Norway. They also noted chaetognaths in 
boluses. The Pacific Ocean representative, Pacific spiny 
lumpsucker, studied in the Gulf of Patience off the east- 
ern coast of Sakhalin Island in Russia, feeds mainly on 
hyperiids, euphausiids, and decapod larvae (Tabunkov 
and Chernysheva, 1985). 
The most recent study on the diet of a lumpsucker 
species (Antonenko et al., 2009) stated that the Siberian 
lumpsucker (EZ. asperrimus) feeds almost entirely on the 
hyperiid T: japonica in the waters of the Primorsky Krai 
(Maritime Territory) of Russia. Primno macropa and 
euphausiids of the genus Thysanoessa were rarely found. 
According to Chuchukalo et al. (1999), E. tartaricus 
feeds equally on both planktonic hyperiids and on young 
boreopacific armhook squid (Gonatopsis borealis) in the 
northern part of the Sea of Okhotsk. Spinous lumpfish 
studied in the Sea of Okhotsk fed mostly on hyperiids, such 
as Themisto japonica and T. libellula, and on euphausiids, 
including Thysanoessa raschii and Thysanoessa sp.; juve- 
nile squid, pteropods, mysids, polychaetes, gammarids, and 
juvenile fish were only occasionally found (Orlov, 1994; 
Melnikov, 1995; Kuznetsova, 1997). There is also a record 
that, in 1993, spinous lumpfish fed mainly on isopods and 
the ctenophore Beroe sp. (Kuznetsova, 1997). Northern 
smoothtongue and leatherfin lumpsucker have feeding 
habits quite similar to that of the Pacific spiny lumpsucker 
(Chuchukalo, 2006). 
Therefore, Fedorov’s lumpsucker, similarly to other 
studied species of Eumicrotremus, feeds on actively 
moving crustaceans. However, the diet of Fedorov’s 
lumpsucker is differentiated from that of other studied 
congeneric species by the large proportions by mass of 
the diet that are fish and mysids (51.10% and 26.44%, 
respectively; Table 1). Chuchukalo (2006) wrote that the 
narrow food specialization (on hyperiids and euphausiids) 
of most lumpsucker species is not typical for plankton- 
eating species of fish and is probably attributable to the 
similarity of behavior, morphological features, and close 
ecology of these species. Our research revealed that the 
diet of the Fedorov’s lumpsucker could include almost 
any benthopelagic animal; therefore, the genus Eumi- 
crotremus could be labeled as euryphagous. Because the 
majority of the food items found in specimens stomachs 
in this study were in good condition, it can be presumed 
that food was sucked into the mouths of individuals with 
a stream of water that resulted from a sharp increase in 
the volume of the buccal cavity. 
Size—frequency analyses of oocytes revealed discontinu- 
ous oogenesis (determinate fecundity), group-synchronous 
ovarian organization (release of eggs once in the spawning 
season), and total spawning, following the classification 
of Murua and Saborido-Rey (2003). Similar reproductive 
strategies have been recorded for other representatives of 
Cyclopteridae, such as the smooth lumpsucker (Zhukova 
et al., 2018). 
Semelparous species have very low or exhausted 
reserves of PG oocytes in prespawning gonads (Mouchlian- 
itis et al., 2019). The presence of quite a lot of PG oocytes 
in all examined ovaries and of primary spermatogonia in 
testes examined in our study confirms that the Fedorov’s 
lumpsucker is an iteroparous species. 
The chorion and thick zona radiata present in ovaries of 
Fedorov’s lumpsucker correspond to the condition of eggs in 
