308 



Fishery Bulletin 104(2) 



^ 0.9 



E 



S O.Qi 



cc 



0.7 



0.6 



0.5 



6 7 8 



Carapace length (mm) 



10 



Figure 3 



Scatter plot of rostrum length/carapace length (RL/CL) ratios 

 against CL for juveniles of Farfantepenaeus brasiliensis (A) 

 and F. notialis (0) from (A) Rio Lagartos and (B) Yalahau 

 lagoons. The separation between species at RL/CL = 0.70 is 

 indicated by a dotted line. 



of RL/CL ratios against CL by species fell into 

 two distinct clouds representing dissimilar mor- 

 phometric characteristics of the species, with the 

 point of separation between species set at a value 

 of 0.70 (Fig. 3). The RL/CL ratios were signifi- 

 cantly higher in F. brasiliensis than in F. notialis, 

 both for Rio Lagartos (ANOVA, F^ 72,5 = 1'778.33, 

 P<0.001) and Yalahau (ANOVA Fji2505=16627.64, 

 P<0.001). For Rio Lagartos, F. brasiliensis had a 

 mean RL/CL ratio ±SD of 0.78 ±0.04 and a range 

 of 0.70-0.92, whereas the mean RL/CL ratio in F. 

 rwtialis was 0.63 ±0.04, with a range of 0.50-0.72. 

 In Yalahau lagoon, the RL/CL ratio in F. brasil- 

 iensis was 0.80 ±0.05 (range 0.68-0.94), where- 

 as in F. notialis these values were 0.62 ±0.05 

 (0.43-0.69; Fig. 4). The above values indicate a 

 morphometric divergence between the two species, 

 with higher values corresponding to F. brasiliensis 

 and lower ones to F. notialis. 



Small juveniles presented clear differences be- 

 tween species in the shape and position of the 

 rostrum with respect to the segments and the 

 flagellum of the antennule. Farfantepeaeus brasil- 

 iensis had a rostrum that was straight and slen- 

 der, extending beyond the 3'^'^ antennular segment, 

 and generally reaching the broadened portion of 

 lateral flagellum (Fig. 5A), whereas F. notialis had 

 a lightly convex rostrum, never extending beyond 

 the third antennular segment (Fig. 5B). 



Discussion 



We found clear morphometrical and morphologi- 

 cal rostrum differences between small juveniles 



