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FISHERY BULLETIN: VOL. 78, NO. 3 



1 r 



70 80 90 100 



STANDARD LENGTH (mm) 



Figure 4. — Relationships (on logarithmic scales) between standard length and gill raker "area" (see text) for 10 species of mesopelagic 

 fishes designated by initials of genus and species names. Lines for Lampanyctus steinbecki, L. nobilis, Triphoturus nigrescens, 

 Ceratoscopelus warmingi, Benthosema suborbitale, Diaphus perspicillatus, and D. trachops are drawn from equations determined by 

 least squares linear regression on the logarithms of the data from five or more specimens of each species over the size ranges plotted; 

 coefficients of determination (r^) exceeded 0.89 for all shown and also for Bolinichthys longipes. D. schmidti, and D. fragilis whose 

 relationships were so similar to those of one or more species illustrated that they were omitted for clarity. Notolychnus valdiviae (r^ = 

 0.26, dashed lines) and Diogenichthys atlanticus (r^ = 0.09) emd Melamphaes danae ir^ = 0.23) are represented by the areas enclosed by 

 points from five specimens each. 



rakers of all four were thin, cylindrical in cross 

 section, and covered with short rasplike teeth; 

 while those of the other species were flattened 

 usually with sawlike teeth on the leading edge. 

 Thus these species seem best adapted for detecting 

 the more visible prey and for retaining only rela- 

 tively large items. 



Ceratoscopelus warmingi and D. perspicillatus 

 had the largest lenses of any species and sizes 

 considered. For both species the ASV's of many 

 types of prey were high, indicating that they are 

 capable of searching greater volumes than species 

 with smaller lenses. Ceratoscopelus warmingi, 

 however, preferred relatively large prey while D. 

 perspicillatus showed high ASV's for small as well 

 as large types. Consonant with these differences 

 in diet, C warmingi had a relatively larger gape 



and less closely spaced gill rakers than did D. 

 perspicillatus. 



Diogenichthys atlanticus, Benthosema subor- 

 bitale, Bolinichthys longipes, and Diaphus 

 trachops also had relatively large lenses; if 

 Diogenichthys atlanticus or Benthosema subor- 

 bitale grew as large as C. warmingi or Diaphus 

 perspicillatus, their lenses would be larger. The 

 first three species' diets included high fractions of 

 microzooplankton. Diogenichthys atlanticus, 

 which had the largest relative lens size and small- 

 est gape, had eaten the widest variety of micro- 

 zooplankton including many forms probably less 

 visible than the Oncaea spp., which dominated the 

 microzooplankton eaten by B. suborbitale and 

 Bolinichthys longipes. Bolinichthys longipes, 

 which was the only species which ate the small 



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