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Fishery Bulletin 99(2) 
this depth (group B), adults and juveniles from other two 
depth categories (groups C and D). 
Group A, juveniles (size 1) from 1800-2250 m 
In 68 specimens analyzed, benthopelagic calanoid cope- 
pods (Table 2) were the most important prey {%IRI= 56.26). 
Benthic tanaidaceans were secondary (Fig. 2A), despite 
having a low overall weight, because they were frequently 
captured ( W/specbnen=0.0Q01 g). Amphipods were the 
most abundant accidental prey item (%7f?/=15.27) owing 
mainly to the weight of Rhachotropis sp. and other amphi- 
pods (Fig. 2A). 
Group B, adults (size 2) from 1800-2250 m 
Calanoid copepods predominated in the 25 adult specimens 
analyzed (%1RI- 79.52), whereas suprabenthic mysids were 
Figure 1 
Dendrogram of disimilarity between diets of different 
groups (bathymetric and ontogenetic) of Bathypterois 
mediterraneus . l=immature (size 1) individuals of 
1000-1425 m depth; 2 = mature (size 2) individuals of 
1000-1425 m depth; 3 = immature (size 1) individuals of 
1425-1800 m depth; 4 = mature (size 2) individuals of 
1425-1800 nr depth; 5 = immature (size 1) individuals of 
1800-2250 m depth; 6 = mature (size 2) individuals of 
1800-2250 m depth. Groups identified: A = 5; B = 6; C = 3, 
4; and IJ = 1,2. 
secondary because of their high weight (Fig. 2B). Benthic 
cumaceans were the major accidental prey (%IRI= 9.6) 
because of high numerical abundance (Fig. 2B). 
Group C, 1425-1800 m 
In 95 specimens analyzed, the most important prey were 
benthopelagic calanoid copepods; their high frequency and 
abundance (Fig. 3) resulted in a %IRI of 95.49%. Incidence 
of other prey was minimal, %IRI <1.5. 
Group D, 1000-1425 m 
In 94 specimens analyzed, planktonic benthopelagic cala- 
noid copepods were the most important prey (%1RI= 88.72). 
Suprabenthic mysids were the major accidental prey 
because of their high mass (%W=43.11 %) (Fig. 4). 
Trophic diversity values ( H\ Table 2) were lowest at 
depths of 1425-1800 m, highest in adults from 1800 to 
2250 m, and higher in adults than juveniles for all the 
bathymetric zones analyzed. Dietary overlap (Table 3) was 
higher between groups 1000-1425 m and 1425-1800 m. 
Affinity between the diets of juveniles from 1800 to 2250 
m and all other groups was low. 
Discussion 
According to Sulak (1977), Bathypterois species feed on 
benthopelagic plankton. Our study shows that Bathypter- 
ois mediterraneus, on the deep slope in the Catalan Sea, 
feed mostly on benthopelagic plankton (calanoid copepods), 
although occasionally on benthic resources (mainly supra- 
benthic form; occasionally endobenthic cumaceans, tanaid- 
aceans, etc; or epibenthic amphipods). The long and thin 
laminar gill rakers of Bathypterois mediterraneus (Car- 
rasson and Matallanas, 1994) are highly adapted for retain- 
ing planktonic prey and indicate filter feeding. Munk (1965) 
noted that Bathypterois have minute eyes, probably of lim- 
ited use in feeding. However, Collin and Partridge (1996) 
suggest that Bathypterois dubius may use two retinal area 
specializations in feeding. Bathypterois mediterraneus may 
exhibit similar behavior. However, there are no photographs 
of Bathypterois with an open mouth that might confirm 
filter feeding. The small size of Bathypterois mediterraneus 
is important in its feeding because Sulak (1984b) postu- 
lated that small-bodied components of the abyssal fauna 
are microphagous (e.g. Bathypterois longipes). 
Bathymetric differences were found in the diet oi Bathy- 
pterois mediterraneus. The prey consumed changed with 
depth, mainly at 1800-2250 m, where juveniles, in addi- 
tion to benthopelagic calanoid copepods, also fed on endo- 
benthic and epibenthic prey, mostly tanaids (80% of them 
found in individuals from a catch at a depth of 2250 m). 
Although a sample taken at 1800 m did not indicate a 
greater abundance of tanaids than in shallower waters 
(800-1000 m) (Cartes 1 ), it is probable that tanaid abun- 
1 Cartes, J. 1998. Personal commun. Institut Ciencies del Mar 
(CSIC), P. Joan de Borbo s/n, 08039 Barcelona, Spain. 
