Colmenero et al.: Reproductive strategy of Lophius piscatorius in Mediterranean waters 
63 
Oocyte development and fecundity 
Oocyte diameters obtained from 21 randomly selected 
specimens at all phases of maturity were measured to 
the nearest 0.01 pm with an image analysis program 
(Image-Pro Plus, vers. 5.0, Media Cybernetics, Inc., 
Rockville, MD) in combination with an Axioskop 2 Plus 
microscope (Carl Zeiss Microscopy, LLC, Thornwood, 
NY), and a ProgRes C14 digital microscope camera 
(Jenoptik AG, Jena, Germany). Only oocytes sectioned 
through the nucleus were taken into account. The de- 
velopmental stages of the oocytes were categorized ac- 
cording to the descriptions in Colmenero et al. (2013) 
that were adapted from Wallace and Selman (1981). 
The mean oocyte diameter by developmental stage was 
determined by calculating the diameter of all oocytes 
encountered in each subsample, and the range was set 
with the smallest and largest oocytes found at each de- 
velopmental oocyte stage. 
Fecundity was determined by using the gravimetric 
method described by Hunter and Goldberg (1980). Be- 
cause homogeneity in oocyte distribution within ovaries 
of white anglerfish has already been established (Afon- 
so-Dias and Hislop, 1996), ovarian tissue subsamples 
of approximately 500 mg were taken randomly from 
2 specimens with ovaries in phase III that had nei- 
ther postovulatory follicles nor atretic oocytes present. 
Whole tissue subsamples were placed on several slides 
and covered with cover slips, then photographed with 
a Canon Powershot SD870 IS digital camera (Canon 
USA, Melville, NY). Oocytes were counted manually 
with Image-Pro Plus. 
Batch fecundity (BF), the total number of hydrat- 
ed oocytes produced in a single spawning event by an 
individual female, of each female was determined by 
means of this equation: 
BF = {oocyte number / sampled GNW) x total GNW, (4) 
where BF is the product of the number of secondary 
vitellogenic oocytes per unit of weight multiplied by 
the total ovarian weight (Yoneda et al., 2001). Relative 
batch fecundity (RBF), the total number of mature eggs 
released by a female during the spawning batch per 
gram of female GW, was calculated with the following 
equation (Pavlov et al., 2009): 
RBF = BF / GW. (5) 
Potential fecundity was calculated as the number 
of vitellogenic oocytes divided by TW in kilograms for 
each mature female and then averaged (Murua et al., 
2003). 
Results 
Gonad morphology 
j The gonad of female white anglerfish has 2 ribbon-like 
ovarian lobes connected to each other at their posterior 
end. One side of the “ribbon” consists of an ovigerous 
membrane from which a single layer of oocyte clus- 
ters, which contain oocytes at different developmental 
stages, projects into the lumen. The other side is no- 
novigerous and secretes a gelatinous material during 
maturation that fills the ovarian lumen, where mature 
oocytes develop (Fig. 2). During maturation, the gonad 
increases in size until it fills the abdominal cavity (Fig. 
3 ). Testes are a pair of elongated organs with a bean 
shape in transverse section. Spermatogenesis takes 
place in a capsule-like sac called a cyst, but it is com- 
pleted in the lumina of the lobules. The cysts appear to 
be arranged with a gradient of germ cells of increasing 
maturation from the cortex to the sperm duct (Fig. 4). 
Spawning season 
The monthly distribution of maturity phases (Fig. 5) 
revealed a peak in reproduction during spring, when 
a major portion of the spawning females and the high- 
est value of GSI (0.77) were found. Spawning capable 
females (phase III) were caught primarily between 
April and June, and females in the actively spawning 
phase (IV) were observed in November, December, and 
March — the latter month having the maximum occur- 
rence (11%). Females in immature, regressing, and de- 
veloping or regenerating phases (I, V, and II, respec- 
tively) were found year-round, although the highest 
percentage of immature individuals (49%) was observed 
in January. The GSI values followed the same pattern 
shown in these maturity phases: highest during spring, 
decreasing during summer and autumn, and increas- 
ing again during winter. Males in all maturity phases 
were observed throughout the year, but with a maxi- 
mum percentage of mature males (66%) in February 
and March. Immature males were found primarily in 
July (69%). The mean GSI for females increased as 
their ovaries developed and peaked in phase IV. For 
males, the mean GSI increased with testicular develop- 
ment and reached a maximum in phase IV (Table 1). 
The mean HSI for females and males increased during 
the summer and autumn months and decreased during 
winter and spring. On the basis of these observations, 
a main spawning season was found from February 
through June and a secondary one occurred in Novem- 
ber and December. 
Size at sexual maturity 
The maturity ogive for males indicates that the length 
at which 50% of them reached sexual maturity (L50) 
was 48.4 cm TL (Fig. 6A). Maturity in males occurred 
at about 37% of their maximum observed TL. The 
smallest mature male found was 32.5 cm TL, and the 
largest immature male was 50 cm TL. The maturity 
ogive for females indicates that L50 was 59.9 cm TL 
(Fig. 6B). Female maturity occurs at about 30% of their 
maximum observed TL. Like the smallest male, the 
smallest mature female was 32.5 cm TL. The largest 
immature female measured 56 cm TL. The maturity 
ogive for the sexes combined indicates an L50 of 51.3 
