AN INVERSE CORRELATION BETWEEN MERISTIC CHARACTERS 



AND FOOD SUPPLY IN MID-WATER FISHES: 



EVIDENCE AND POSSIBLE EXPLANATIONS 



Robert Karl Johnson' and Michael A. Barnett^ 



ABSTRACT 



In five species of mid-water fishes, Chauliodus sloani, Diphphos taenia, Pollichthys mauli, Vin- 

 ciguerria lucetia, and V. nimbaria, the central values of meristic counts (anal fin rays, vertebrae, 

 longitudinal photophore rows) and three measures of biological productivity (phosphate-phosphorus 

 concentration, net primary production, zooplankton standing stocks) are correlated negatively. For the 

 species and areas studied the meristic variation observed cannot be related to temperature, salinity, 

 dissolved oxygen, or any other physical or chemical factor known to affect meristic variation in fishes. 

 It is hypothesized that this relationship between meristic counts and measures of food availability 

 involves differences in egg size, fecundity, size at hatching, and size at comparable stages of larval 

 development between populations in different areas, and that these differences in turn reflect adap- 

 tations to low food densities in areas of low productivity and higher predator densities in areas of 

 higher productivity. 



Meristic characters have been widely used in 

 studies of fish populations and species. Unlike 

 body proportions or coloration, meristic characters 

 are fixed usually at or before metamorphosis and 

 remain constant throughout the life of an in- 

 dividual. Variation in meristic characters stems 

 from both genetic variation between populations 

 and species, and from environmental variation, 

 which, within genetically controlled limits, can 

 directly affect the number of parts formed in 

 developing embryos and larvae. Recent reviews of 

 factors known to affect meristic characters in 

 fishes include Barlow (1961), Blaxter (1969), Gar- 

 side (1966), and Fowler (1970). 



An inverse relationship between vertebral and/ 

 or other meristic counts and water temperature 

 at the time of early development has been 

 demonstrated in numerous studies (see above 

 review articles). Experimental studies have shown 

 that in many cases the effect of temperature upon 

 meristic characters occurs within a restricted 

 period of time, the so-called sensitive period, and 

 that variations in temperature before and after 

 this period have no effect (Hempel and Blaxter 

 1961). The sensitive period may vary with 



'Division of Fishes, Field Museum of Natural History, 

 Roosevelt Road at Lake Shore Drive, Chicago, IL 60605. 



^Scripps Institution of Oceanography, University of Califor- 

 nia, San Diego, La JoUa, CA 92037. 



different structures with the result that the tim- 

 ing, magnitude, and in some cases the direction of 

 response of different structures to temperature 

 variation differs among different species (Fowler 

 1970). 



Hubbs (1926), Barlow (1961), and others, have 

 suggested that the relationship between meristic 

 counts and temperature involves differential ef- 

 fects of temperature on rate of growth versus rate 

 of differentiation, with the result that accelerated 

 growth is associated with a shortening of the sen- 

 sitive period, resulting in the laying down of fewer 

 parts. The conclusion is that conditions retarding 

 growth rates are associated with elevated meristic 

 counts, conditions accelerating growth rates are 

 associated with lowered meristic counts. This 

 explanation has been extended to factors other 

 than temperature known to affect meristic 

 characters in fishes: dissolved oxygen concentra- 

 tion (Alderdice et al. 1958), salinity (Forrester and 

 Alderdice 1966; Blackburn 1967), carbon dioxide 

 concentration, light intensity, exposure to X-rays, 

 etc. (see Fowler 1970). 



In 1972, we reported a significant negative 

 correlation between certain meristic counts in 

 Diphphos taenia and three measures of food sup- 

 ply: net primary production, phosphate- 

 phosphorus concentration, and zooplankton 

 standing stocks (Johnson and Barnett 1972). To 

 our knowledge, this was the first suggestion of a 



Manuscript accepted July 1974 



FISHERY BULLETIN; VOL. 73, NO. 2, 1975 



284 



