ABSTRACT. Larval development of Brycon hilarii (Characiformes, Characidae). The present study characterizes the early stages of development of Brycon hilarii (Valenciennes, 1850) based on morphometric and meristic characters. Patterns of development in morphometric characters were analyzed through the fit of linear, quadratic and linear piecewise models. Samples were collected from March 2000 to March 2004 in basins of the Cuiabá and Manso rivers, state of Mato Grosso, Brazil. Larvae were identified and classified in different stages (Larval Yolk, Pre-Flexion, Flexion, and Post-Flexion) according to notochord development. The morphometric and meristic characters for each larva were, respectively, measured and counted. The standard length ranged from 3.25 to 26.00 mm. The Larval Yolk stage showed a greater concentration of dendritic pigments along the intestine, and the Flexion and Post-Flexion stages showed an intensified pigmentation intensified along the back. A single spot on the humerus and another on the caudal peduncle were observed at the end of the Post-Flexion stage. Also, in the Larval Yolk and Pre-Flexion stages. The intestine is long, the snout is short, the adhesive organ was present in the Larval Yolk and Pre-Flexion, and the mouth is terminal throughout the development. The total number of myomeres ranged from 41 to 50 (23 to 30 pre-anal and 16 to 24 post-anal). Number of fin rays: dorsal 11; anal 30; pectoral 15 and ventral eight. The analysis of the development indicated higher metamorphosis in the Flexion stage.KEYWORDS. Morphology, larvae, fish, piraputanga, Paraguai river basin. RESUMO. O presente estudo caracterizou o desenvolvimento inicial deBrycon hilarii (Valenciennes, 1850) através de caracteres morfométricos e merísticos e analisou as relações entre as características morfométricas das larvas ao longo do desenvolvimento usando modelos de regressão linear, quadrática e linear por partes. O material foi obtido nas bacias dos rios Cuiabá e Manso, Mato Grosso, Brasil, entre março de 2000 e março de 2004. Os indivíduos foram identificados e separados de acordo com o grau de desenvolvimento da notocorda e, posteriormente, medidos e contados os caracteres morfométricos e merísticos, respectivamente. O comprimento padrão variou entre 3,25 e 26,00 mm. Inicialmente, as larvas apresentaram maior concentração de pigmentos dendríticos ao longo do intestino e, em flexão e pós-flexão, intensificaram-se no dorso do corpo. Uma mancha umeral e outra no pedúnculo caudal foram observadas no final do estágio de pós-flexão. O intestino apresentou-se longo, o focinho curto, o órgão adesivo presente em larval vitelino e pré-flexão e a boca terminal por todo o desenvolvimento. O número total de miômeros variou de 41 a 50 (23 a 30 pré e 16 a 24 pós-anal). O número de raios das nadadeiras foi: dorsal 11; anal 30; peitoral 15 e ventral oito. A análise do crescimento indicou maior metamorfose no estágio de flexão. PALAVRAS-CHAVE.Morfologia, larva, peixe, piraputanga, bacia do rio Paraguai.
Abstract:The Neotropical region exhibits the largest diversity of fish worldwide; however, little is known about the early development of fish species from this region. Therefore, to contribute to this knowledge, this study aimed to morphologically describe the early stages of development (eggs, larvae and juveniles) of S. pappaterra using morphometric and meristic traits, and to assess changes in growth rates throughout larval and juvenile development by analyzing the relationships between various morphometric traits using analytical regression models. Both juvenile and adult individuals with mouth-brooded offspring were collected along the basins of the Cuiabá and Manso Rivers in the state of Mato Grosso, Brazil between March 2000 and March 2004. After the adults were identified, the offspring were classified according to its stage (embryonic, larval or juvenile period), and various morphometric and meristic variables were individually measured (when possible). The eggs of this species are yellow in color, oval shaped, show dendritic pigmentation within their yolk, have small to moderately sized perivitelline spaces and lack a mucous membrane and oil droplets. The horizontal and vertical diameters of the sample yolks ranged from 1.43mm to 2.70mm and 1.05mm to 1.68mm, respectively. The standard length of the larval period varied from 4.30mm to 7.16mm, and the standard length of the juvenile period varied from 10.29mm to 24.57mm. Larvae exhibit yolk sacs with internal dendritic pigmentation and dark punctate pigmentation in the dorsal and ventral body regions, whereas irregular transverse spots along the flanks are observed during the juvenile period. Adhesive organs are only present during the yolk-sac stage and at the beginning of the flexion stage. The mouth is terminal during all stages of development. The myomere number varied from 22 to 29 (9 to 16 pre-anal and 10 to 16 post-anal), and the maximal numbers of fin rays and spines were as follows: dorsal, xvI+10; anal, Iv+8; pectoral, 16; and pelvic, I+8. Growth analyses identified periods of important change in larval morphology (i.e., metamorphosis), particularly during the flexion and post-flexion stages and in juveniles. Therefore, the morphological development of S. pappaterra is consistent with the ecological requirements of this species, which primarily occurs in structured lentic environments with aquatic macrophytes. Rev. The greatest difficulty inherent to the study of freshwater ichthyoplankton is properly identifying fish eggs and larvae in their natural environments. This difficulty stems largely from the significant morphological similarities between different taxonomic groups during early stages of development (Bialetzki, Sanches, Baumgartner, & Nakatani, 1998) and because species spawn in the same areas at the same times of the year (Nakatani et al., 2001). Hence, the taxonomic characterization of early fish development could help us to better understand the ecological relationships between species during development within their natural envir...
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