Gordeev et al.: The first data on the diet and reproduction of Eumicrotremus fedorovi 35 
at the late vitellogenetic and periovulatory macroscopic 
phases of gonadal maturity. A piece of ovarian tissue was 
taken from the median portion of the gonad from each spec- 
imen. The subsample of each ovary, representing 5—10% of 
the gonad weight, was weighed, and all advanced oocytes 
(1.7—2.3 mm in diameter) in the subsample were counted. 
The gonadosomatic index (GSI) and absolute (F,,,) and 
relative (F,,,) fecundity were estimated as follows: 
GSI = (GW x 100)/ BW, (1) 
F ps = (n x GW) /w, and (2) 
F,., = (n x GW)/(w x BW), (3) 
where n = the number of advanced oocytes in the subsample; 
w = the weight of the subsample (in grams); 
GW = the gonad weight (in grams); and 
BW = the body weight (in grams) of the specimen. 
Standard deviations, Pearson’s correlation coefficients 
(r), Spearman rank correlation coefficients (p), and P-values 
were calculated by using Microsoft Excel 2010 (Microsoft 
Corp., Redmond, WA) and statistical software R, vers. 3.6.3 
(R Core Team, 2020). 
Results 
Diet 
The stomachs of most of the specimens examined were 
full. The level of digestion in most cases made it possible 
to determine the species or taxon of food items. The weight 
of the boluses ranged from 9 to 3727 mg. Young walleye 
pollock (Gadus chalcogrammus), 36-61 mm TL; north- 
ern lampfish (Stenobrachius leucopsarus), 18-25 mm 
TL; and northern smoothtongue (Leuroglossus schmidti), 
19-23 mm TL, as a group accounted for the majority of 
fish food items (Table 1). Walleye pollock were found in 
Table 1 
Frequency of occurrence and proportion of the total mass 
of food items found in the stomach contents of Fedorov’s 
lumpsucker (Eumicrotremus fedorovi) caught during 19-25 
March 2017 off Simushir Island, located near the center of 
the Kuril Islands in the northwest Pacific Ocean. 
Occurrence Mass 
of food items proportion 
Food item (%) (%) 
Gadus chalcogrammus 69.57 40.55 
Hyperiida 65.22 14.03 
Mysida 62.32 26.44 
Calanoida 52.17 3.98 
Gammarida 44.93 3.86 
Stenobrachius leucopsarus 40.58 9.93 
Leuroglossus schmidti 2.90 0.65 
almost 70% of stomachs and composed over 40% of the 
total weight of boluses collected from the specimens with 
food in their stomachs (65 of 69 specimens). 
After walleye pollock, crustacean species were the most 
frequent food items (Table 1). Hyperiids were represented 
by only 2 species—Themisto pacifica and Primno macropa. 
Copepods were represented by several species of Cala- 
noida, including Neocalanus cristatus, Gaetanus minutus, 
Paraeuchaeta elongata, Onchocalanus magnus, Pseu- 
dochirella obtusa, Cornucalanus indicus, Scaphocalanus 
sp., and Neocalanus spp. All calanoids were adults in the 
final development stage. Paraeuchaeta elongata was the 
most common copepod found in stomachs. Unfortunately, 
representatives of Mysidae lost most of their identifying 
characteristics when they were eaten by Fedorov’s lump- 
sucker, and we could not identify them to the lowest taxon. 
Gammarids were represented by Cyphocaris challengeri 
(most commonly), Photis reinhardi, and a few specimens 
from the families Phoxocephalidae and Lysianassidae. 
In addition to the taxa given in Table 1, there were sev- 
eral minor food items—2 specimens of Caprelloidea, both 
belonging to the family Caprellidae; a few small shrimp; 
the digested remains of fish from an unknown species; 
and a single squid, whose morphological features indicate 
that it is a specimen of either the Taonius belone or the 
Gonatopsis borealis. 
Reproduction 
Female Fedorov’s lumpsucker have a pair of elongated ova- 
ries attached to the dorsal wall of their body cavity. Ovaries 
at the phase of onset of vitellogenesis were small and flac- 
cid, with no oocytes visible to the eye. Results of histological 
analysis indicate the presence of oocytes at the stage of PG, 
with some oocytes at the Vtgl stage and oocytes sporadi- 
cally at the Vtg2 stage (Fig. 2A). Oocytes at the PG stage 
had a mean diameter (@) of 128 pm (SD 48) (Fig. 3), were 
ovoid, with basophilic cytoplasm and a large round nucleus 
in central position, and were found in all gonads (Fig. 4, A 
and D). Oocytes at the stage of Vtg1 had a mean @ of 325 pm 
(SD 103) and were characterized by secondary growth at the 
beginning of vitellogenesis. Compared with that of the PG 
oocytes, the cytoplasm of the Vtg1 oocytes was more acido- 
philic with cortical alveoli, scattered yolk granules, and oil 
droplets (Fig. 4, A, B, and D). 
Oocytes at the stage of Vtg2 had a mean @ of 533 pm 
(SD 102), were characterized by cytoplasm partially filled 
with yolk, and were found in gonads in the mid- and late 
vitellogenic phases (Fig. 4, A, B, and D). Early vitellogenic 
gonads were bigger and less flaccid than ovaries at the 
onset of vitellogenesis and had scattered, visible small 
eggs with @ less than 1 mm. Most germ cells were at the 
stages of PG and Vtg1, and Vtg2 germ cells were also 
found (Fig. 2B). Mid-vitellogenic ovaries were light orange 
in color, and oocytes were visible to the eye with @ of about 
1 mm. In such gonads, Vtg2 was the prevailing stage of 
oocytes (Fig. 2C). Late vitellogenic ovaries were dense and 
bright orange in color, and oocytes were clearly visible 
with @ from 1.0 to 1.6 mm (Fig. 2D). Most germ cells in 
