NOTE May-Ku et al Morphological differentiation between small |uveniles of Farfantepenaeus brasiliensis and F notiolis 



309 



(4-8 mm CL) of F. brasiliensis and F. notialis in two 

 coastal lagoons of the Gulf of Mexico. Our results also 

 complement those obtained by Perez-Farfante (1969; 

 1970, 1971a) because the unique characters of the ros- 

 trum highlighted by that author for juveniles 28 mm CL 

 persisted in our study for small juveniles (<8 mm CL). 

 We also found interspecific differences in the growth pat- 

 terns given by the RL-CL relationship (slopes) and in the 

 RL/CL ratio (intercept differences). These results have 

 important implications. Dall et al. (1990) mentioned that 

 the shape and increase in size of different body struc- 

 tures in crustaceans depend on the species, age, sex, and 

 the surrounding environment. Our comparison of the 

 regression lines between RL and CL of the two shrimp 

 species analyzed in the present study, coming from Yala- 

 hau and Rio Lagartos lagoons, showed unambiguously 

 that the growth pattern, or degree of change in RL in 

 relation to CL, differed between the two species at all 

 sizes of the specimens. Different intercepts, on the other 

 hand, implied that although the growth patterns may be 

 the same over the size range measured (regression lines 

 are almost parallel), the relative body proportions of both 

 species are different. These differences are likely due to 

 different growth rates at some earlier size (Haddon and 

 Willis, 1995). Both types of difference imply that the 

 relative proportions of the body, or the body shape, are 

 distinct for the species analyzed (Haddon and Willis, 

 1995). An analysis of the RL-CL relationship revealed 

 that, at a given CL, the RL in F. brasiliensis grows 

 1.23-1.29 times faster than in F. notialis. On the other 

 hand, the marked differences in the RL/CL ratio imply 

 that this morphometric character is species-specific and, 

 at a given CL, the pink spotted shrimp has a consistently 

 longer rostrum than southern pink shrimp, with a value 

 of 0.70 as a point of separation between species. These 

 results are also qualitatively observed in the shape and 

 position of the rostrum with respect to the segments and 

 the flagellum of the antennule in both species. 



In conclusion, we successfully separated small juve- 

 niles of two shrimp species that are found in coastal 

 lagoons of the Gulf of Mexico. Both species can be iden- 

 tified by easily observed and quantified rostrum char- 

 acteristics. 



Acknowledgments 



This work is part of the Ph.D. thesis of M. A. May-Kii 

 at CINVESTAV-Merida. Financial support from CONA- 

 CyT Mexico (grant to M.A. May-Kii) is acknowledged. 

 The authors are grateful to M. Ornelas-Roa from the 

 Plankton Laboratory at CINVESTAV-Merida for her 

 help in obtaining morphometric data. Two anonymous 

 referees provided useful suggestions that significantly 

 improved the manuscript. 



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