| Resumo: |
Otoliths (sagitta, asteriscus and lapillus)are complex structures composed of calcium carbonate, other minerals, and a protein matrix. Otoliths are located in the internal ear of the teleost fishes. The shape and structure of otoliths are specific for each species. For this reason, otoliths are used to identify species in biological and ecological studies.Sciaenids conform a group of fishes of commercial importance, so the handling of this resource is a high-priority topic for the local and national economies of countries that exploit these species. The purpose of this work is to study different aspects of the sagittae of marine sciaenids from Argentina and Peru. The morphology, morphometry and chemical composition has been analyzed in relation to the environment. The sciaenids studied from Buenos Aires coast are: Cynoscion guatucupa, Macrodon ancylodon, Menticirrhus americanus, Micropogonias furnieri, Paralonchurus brasiliensis and Umbrina canosai, while from Grau (Peru)they are: Cynoscion analis, Larimus acclivis, Micropogonias altipinnis, Paralonchurus brasiliensis and Sciaena deliciosa. The identification of fishing stocks species through the morphology, morphometry and elemental composition of the sagittae is evaluated. Moreover, the elemental composition has been evaluated in order to be used as bioindicator of environmental conditions. An otolith specific identification key has been elaborated using the characteristics of the topography of internal and external faces and of the lateral view of sagitta. Generic morphological patterns and intraespecific variations related with changes in the development of the fish have been analyzed. Morphological variations have been found in the sagittae of C. guatucupa, C. analis, M. americanus, M. furnieri and P. brasiliensis associated to changes in physical and chemical parameters of the habitats that would produce changes in the deposition of the calcium carbonate on the sagitta during the life cycle. Morphological and morphometrical variability has been recorded in the sagittae of M. furnieri adults coming from different coastal localities from Buenos Aires, which allows to infer the presence of at least two population groups. The morphometric analysis showed no differences in the right and left sagittae of each species. The dimensions of the sagittae are mainly influenced by environmental factors (temperature, salinity and latitude)and somatic growth of the fish, while the dimensions of ostium and cauda would be mainly influenced by the genetic pattern, the evolutionary history of the species and the ontogeny. For C. guatucupa, M. americanus, M. furnieri and C. analis, a negative correlation of the temperature and a positive one of the salinity and latitude with the morphometric characteristics of the sagittae were recorded (i.e. sagittae of bigger size at low temperature, and high latitude environments). The analysis of trace elements of the sagittae showed that they precipitate homogeneously on the surface of the otolith. The sagittae of M. furnieri have some elements (strontium and potassium)in common in all the coastal localities studied from Buenos Aires, while phosphorus and chromium were present only in otoliths from Partido de La Costa, and cadmium in the ones from San Blas. The presence of particular elements might related with the type of antropic pollution that would influence the nursery areas of fishes. As a consequence, sagittae could be used as bioindicadors of water quality. The sagittae of C. guatucupa, M. ancylodon, M. americanus and M. furnieri have higher relative concentration of strontium in San Blas than in Partido de La Costa. This may be associated to differences in temperature between both areas that would affect the precipitation of strontium. This characteristic could be an useful tool for the identification of fishing stocks from Buenos Aires
Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales
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