621 
Can scales be used to sex 
winter flounder, 
Pleuronectes americanus? 
Allen J. Bejda 
Beth A. Phelan 
James J. Howard Marine Sciences Laboratory 
Northeast Fisheries Science Center 
National Marine Fisheries Service, NOAA 
Highlands, New Jersey 07732 
E-mail address (for A. J. Bejda): allen.bejda@noaa.gov 
nearest millimeter total length. 
Using the method described by Lux 
and Porter ( 1963), we palpated the 
blind side of the caudal peduncle 
noting either roughness (males) or 
smoothness (females). The fish 
were then dissected to determine 
(visually) maturity and sex. All 
immature fish were eliminated 
from the study. When possible, a 
sample of ten or more scales was 
taken from the palpated area. In 
the laboratory, the scales were ex- 
amined with a dissecting micro- 
scope to determine their type and 
relation to texture. 
We tested the accuracy of a tech- 
nique to rapidly determine the sex 
of mature winter flounder, Pleuro- 
nectes americanus * in the field with- 
out sacrificing individuals. Al- 
though a number of techniques have 
been developed for sexing fish by 
examining reproductive anatomy 
(Moen, 1959; Driscoll, 1969; Martin 
et al., 1983; Ross, 1984), they are 
not well suited for easy and rapid 
determinations in the field. Exter- 
nal characteristics, such as features 
of the urogenital region (Sigler, 
1948; McComish, 1968; Flickinger, 
1969; Lebeau and Pageau, 1989) or 
body shape (Snow, 1963), have been 
successfully applied in the field for 
other species but are not applicable 
to winter flounder which exhibit no 
obvious sexual dimorphism. Some 
studies have suggested that male 
and female winter flounder can be 
differentiated by the texture of the 
scales on the blind side; males al- 
legedly have ctenoid scales which 
feel rough, whereas females alleg- 
edly have cycloid scales which feel 
smooth ( Perlmutter, 1947; Lux and 
Porter, 1963). Unfortunately, the lit- 
erature is inconclusive and none of 
the studies have carefully tested the 
relationship of texture as related to 
scale type and sex. MacPhee (1978) 
citing Norman (1934) claimed that 
scales on the blind side of males are 
ctenoid rather than cycloid when, in 
fact, Norman stated that for the 
species in general the scales are 
ctenoid on the ocular side and cyc- 
loid on the blind side. 
Methods 
From March through September, 
1989, winter flounder were col- 
lected with an otter trawl in New 
Jersey waters. Fish were collected 
at 14 inshore sites in Raritan and 
Sandy Hook Bays (Phelan, 1992) 
and 22 offshore sites 22.2 km east 
of Sandy Hook (Studholme et al., 
1995). Fish were measured to the 
Results and discussion 
A total of 730 mature fish, ranging 
from 12.9 to 39.7 cm, were exam- 
ined. External palpation resulted in 
a significantly higher (% 2 =51.528, 
PcO.OGl) sex ratio (females to 
males) of 2.7:1 than the actual ra- 
tio of 1.2:1 (Fig. 1). The difference 
in the ratios was due primarily to 
males being identified as females. 
Forty six percent (155 of 332) of the 
Manuscript accepted 10 December 1997. 
Fishery Bulletin 96:621-624 (1998). 
■Q 
E 
□ 
600 
500 
E3 Misidentified male 
□ Misidentified female 
Females Males 
True identification 
Females Males 
identification by palpation 
Figure 1 
Number of female and male winter flounder (Pleuronectes americanus ) 
identified by gonadal inspection and palpation of the blind side scales. 
