FISHERY BULLETIN: VOL. 71, NO. 1 



PAIRED FIN LENGTH 



Ginsburg (1954) reported the range of pec- 

 toral fin length taken as a percent of standard 

 length to be 18.0-21.5 and 15.5-19.0 for M. alhidus 

 and M. magnoculus, respectively. The Atlantic 

 specimens examined in the study have a similar 

 maximum value to that of M. alhidus (21.7, see 

 Table 2) but the minimum value obtained, 13.7, 

 is much lower. The minimum value obtained 

 from the Gulf population, 13.7, is somewhat 

 lower than the minimum value recorded for M. 

 magnoculus, while the maximum value obtained, 

 19.4, is similar to that given by Ginsburg for M. 

 magnoculus. Average values calculated from 

 the data in Table 10 in Ginsburg (1954) are 19.8 

 for M. alhidus and 17.0 for M. magnoculus. 

 These compare fairly well with the values ob- 

 tained for the Atlantic and Gulf populations 18.3 

 and 16.8, respectively. 



Table 2. — Pectoral fin length as a percent of standard 

 length for the Atlantic and Gulf populations. 



Table 3. — Pelvic fin length as a percent of standard 

 length for the Gulf and Atlantic populations. 



The range of values for the pelvic fin length 

 expressed as a percent of standard length is 12.8- 



19.2 with an average value of 15.6 for the At- 

 lantic population and 11.6-17.0 with a mean of 



14.3 for the Gulf population (Table 3). Ginsburg 

 also reported a range of 13.5-19.5 for M. alhidus 

 and 12.0-16.0 for M. magnoculus, and the aver- 

 ages computed from data contained in his Table 9 

 are 16.6 and 14.0 for M. alhidus and M. mugnoc- 

 ulus, respectively. 



The present data indicate that the Gulf pop- 

 ulation does have proportionally smaller paired 

 fins than the Atlantic population, however, the 

 differences are much smaller than indicated by 

 Ginsburg. The relative length of the paired fins 

 is similar in both populations and is clearly of 

 no value in separating the two. 



Ginsburg (1954) stated that the growth of the 

 pelvic fin was allometric and that the relative 

 pectoral fin length changed little if any with 

 growth. To compensate for this he arranged 

 his material into several size classes and com- 

 pared similar sizes for both populations. How- 

 ever, he gave no average standard length for 

 the classes, and it is impossible to determine if 

 the size composition of the classes he compared 

 was similar. Figure 3 indicates that growth of 

 the pectoral fin is allometric and not isometric 

 as reported by Ginsburg (1954). The pelvic fin 

 does undergo allometric growth as stated by 

 Ginsburg (see Figure 4). 



Since the material examined from both areas 

 is not of the same size composition (the average 

 standard length of the specimens from the At- 

 lantic population is 283 mm while the average 

 standard length of the specimens from the Gulf 

 population is 323 mm) at least some of the dif- 

 ference in paired fin length is due to allometric 

 growth. 



Figures 3 and 4 indicate that for some of the 

 Gulf material the paired fins are relatively smal- 

 ler than in other specimens of similar sizes. The 

 majority of specimens with the smaller fins were 

 collected north of lat 26°N. Most of the speci- 

 mens with the higher values were collected north 

 of lat 21 °N in the Atlantic. Many specimens ex- 

 amined from the northern Gulf have fins of the 

 same size as specimens from the southern Gulf 

 and Atlantic populations. Hence, not all of the 

 northern Gulf material can be distinguished by 

 relative fin size. 



The paired fins are poor characters to use in 

 Merhiccius because they are generally damaged 

 to some degree. It is often impossible to deter- 

 mine if the fine ends of the rays are broken off. 



86 



