STRUHSAKER and MONCRIEF: BOTHUS THOMPSONI 



variable. Plots of all regressions are linear and 

 exhibit high )^ values. 



The regressions obtained for the 13 measured 

 characters were subjected to analysis of 

 covariance to test for sexual dimorphism. 

 Highly significant differences (P< 0.001) were 

 found between the regression coefficients for two 

 characters (which are related): interorbital dis- 

 tance (Figure 4) and snout to upper eye. Juvenile 

 and adult male specimens of B. thonipsoni are 

 similar to many Bothus spp. males in possessing 

 a much greater interorbital distance than females 

 of the same species. Male B. fliompsoni exhibit 

 positive allometric growth of the interorbital 

 distance, this measurement being about 7.5% - 

 9.0% of standard length at a length of 50-60 mm 

 and about 12% -14% ofstandard length at a length 

 of 100-115 mm. In female specimens longer 

 than 50 mm the interorbital distances were 6.0% - 

 8.6% 'ofstandard length. Interorbital distances of 

 5.3% and 5.1% ofstandard length were noted in 

 two specimens 39 mm and 48 mm long. As ex- 

 pected, male B. thonipficnii exhibited positive 

 allometric growth of the snout to upper eye 

 distance. 



Among the remaining 11 characters subjected 

 to analysis of covariance, there were no signifi- 

 cant differences between regression coefficients. 

 There were significant differences (P<0.05) in 

 the elevations of the regressions between sexes 

 for four characters. Both the upper and lower 

 orbit diameters of males tend to be larger than for 

 females; the differences in adjusted means for 



60 70 60 90 



STANDARD LENGTH (mm) 



Figure 4. — Plots of the interorbital distance of 29 male 

 and 3 1 female specmiens of Boihiis ihonipsciii. 



the two characters are 0.35 and 0.40 mm, re- 

 spectively. Females tend to have a greater body 

 dei)th and a greater snout to greatest body depth 

 distance. The differences in adjusted means for 

 these two characters are 1.1 and 1.0 mm, 

 respectively. 



In both sexes, the pectoral fins of the ocular 

 side tend to be longer than those of the blind side 

 (Table 1). The pectoral fins of both sexes exhibit 

 negative allometric growth. This is most pro- 

 nounced on the ocular size where the pectoral 

 length is about 24% -25% of standard length at 

 40-60 mm and about 18% -21% ofstandard length 

 at a length of 100-115 mm. There is only slight 

 negative allometric growth of the pectoral fin 

 on the blind side where this structure varies 

 from 14.0% to 18.7% ofstandard length. 



All other morphometric characters examined 

 exhibited approximately isometric growth. 



Two of the measurements we obtained for the 

 holotype (Table 1) do not fall within the ranges 

 we obtained from our study series: interorbital 

 distance and snout to upper eye. 



Other morphological characters 



Botlius thonipsoiii has cycloid scales on the 

 blind side and on most of the ocular side (Figure 

 5A). Ctenoid scales occur on the proximal 

 portions of the dorsal and anal rays. There are 

 2-3 rows of ctenoid scales at the bases of the dor- 

 sal and anal fins (Figure 5B). Fowler (1923) 

 stated that the holotype had ctenoid scales on 

 the cheeks and postorbital region. In addition, 

 we find that there is a patch of about 15 ctenoid 

 scales below the curved portion of the lateral 

 line in the holotype. A scale from this region is 

 shown in Figure 5C. The occurrence of ctenoid 

 scales on the cheek and in the vicinity of the 

 curved portion of the lateral line is a variable 

 character. Of 25 specimens (67.5-106.4 mm SL) 

 from our study series, six had ctenoid cheek 

 scales, three had ctenoid scales on the cheek 

 and near the lateral line, and one had ctenoid 

 scales near the lateral line only. The presence 

 of ctenoid scales in these two regions does not 

 appear to be related to size or sex. The cycloid 

 scales are small and nonimbricated, but the 

 ctenoid scales at the dorsal and anal fin bases 

 overlap to a slight degree. The ctenii of the 

 ctenoid scales generally occur in two rows: a 

 primary row of well-developed ctenii and a 

 secondary row of smaller ctenii basal to the 



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