RESUMO
The early life history stages are inadequately known for most fishes of the Neotropical region. Thus, larvae and juveniles of the species Pachyurus bonariensis and Plagioscion ternetzi, two corvina species found in the Pantanal of Mato Grosso, Brazil, were described, assessing ontogenetic changes in their external morphology, pigmentation, fin development, morphometry and meristics. Fish were collected in Chacororé Bay, on the Cuiabá River, between March 2000 and March 2004. Eighty individuals of each species were analyzed, comprising 60 larvae and 20 juveniles. Pachyurus bonariensis larvae exhibited a mouth in a terminal position that became sub-terminal; large, well-pigmented, spherical eyes that became small and elliptical in postflexion; preopercular spines (two internal and four external); 23 to 27 myomeres; initially sparse pigmentation that intensified, mainly in the ventral region; and the following fin formation sequence and total number of spines and rays: caudal, dorsal (XI+29-32), anal (II+six), pelvic (I+five) and pectoral (15-17). In contrast, the larvae of P. ternetzi exhibited a terminal mouth; large, well-pigmented, spherical eyes that decreased in size during development; preopercular spines (three internal and four external); 23 to 26 myomeres; pigmentation that was initially sparse, became evident only in late postflexion stage, with the presence of some chromatophores on the top of the head; and the following fin formation sequence and total number of spines and rays: caudal, dorsal (XI+30-36), anal (II+six), pelvic (I+five) and pectoral (16-18). In relationship the morphometric variables, only the snout-anal fin length differed between the two species, being initially larger in P. ternetzi, whereas it only became larger in juvenile P. bonariensis after 34 mm. Despite the difficulty of intraspecific identification among fish larvae collected in natural environments, the morphological and morphometric tools used in the present study were effective in separating the early stages of development of the two morphologically similar species that share the same environment for reproduction.
Las primeras fases del ciclo de vida no son conocidas lo suficiente para la mayoría de los peces de la región Neotropical. Así la descripción de larvas y juveniles de Pachyurus bonariensis y Plagioscion ternetzi, dos especies de corvinas que se encuentran en el Pantanal matogrossense, Brasil, fue realizada a través de cambios ontogénicos en la morfología externa, en la pigmentación y en el desarrollo de las aletas, al igual que en la morfometría y merística. El material fue recolectado en la bahía de Chacororé, río Cuiabá, entre marzo de 2000 y marzo 2004. Se analizaron 80 individuos de cada especie, siendo 60 larvas y 20 juveniles. Las larvas de P. bonariensis presentaron boca en posición terminal pasando a sub-terminal, ojos grandes, bien pigmentados y esféricos, tornándose pequeños y elípticos en post-flexión, espinas en el pre-opérculo (dos internas y cuatro externas); número total de miómeros variando entre 23 y 27, pigmentación inicialmente escasa intensificándose, principalmente, en la región ventral; secuencia de formación y número total de espinas y radios de las aletas: caudal, dorsal (XI+29-32), anal (II+6), pélvica (I+5) y pectoral (15-17). Por otro lado, las larvas de P. ternetzi presentan una boca terminal: ojos grandes, bien pigmentado y esféricos, disminuyendo a medida que se desarrolla, espinas en el pre-opérculo (tres internas y cuatro externas); número total de miómeros variando entre 23 y 26; pigmentación inicialmente escasa, volviéndose evidente solo al final de la post-flexión, con la presencia de algunos cromatóforos en la región superior de la cabeza; secuencia de formación y número total de espinas y radios de las aletas: caudal, dorsal (XI+30-36), anal (II+6), pélvica (I+5) y pectoral (16-18). En la relación de las variables morfométricas, sólo la longitud de la aleta anal-hocico diferían entre las dos especies, siendo inicial-mente mayor en P. ternetzi, mientras que sólo se hizo más grande en los jóvenes de P. bonariensis después de 34 mm. A pesar de la dificultad de identificación intraespecífica entre larvas de peces recolectadas en ambientes naturales, las herramientas morfológicas y morfométricas utilizadas en el presente estudio fueron eficaces para la separación de las primeras etapas de desarrollo de las dos especies morfológicamente similares que comparten el mismo ambiente para la reproducción.
RESUMO
With the objective to analyze the temporary distribution of Pachyurus bonariensis larvae and its relationship with some environmental variable, collections were carried in the Sinhá Mariana bay, Mato Grosso State, between March/2000 and March/2004, at 4:00 p.m. and at 10:00 p.m. Simultaneously, water samples were obtained to determine temperature of the water, dissolved oxygen, pH and electric conductivity. The largest densities were verified between the months of October and January, suggesting to be this the main period of reproduction of the species. However, larvae in preflexion and flexion were also found in the months of winter, possibly associated to the favorable conditions for the reproduction. Individuals of all of the stages were present, thus it is probable that the whole life cycle happens inside of the bay. The density of larvae more developed in the surface is larger at night, while the initial larvae are found in the surface in both schedules, thus the degree of larval development influences in the distribution pattern of the species in the column of water.
Com o objetivo de analisar a distribuição temporal de larvas de Pachyurus bonariensis e sua relação com algumas variáveis ambientais, foram feitas coletas na baía Sinhá Mariana, Mato Grosso, entre março/2000 e março/2004, às 16 e 22h. Simultaneamente, amostras de água foram obtidas para determinar temperatura da água, oxigênio dissolvido, pH e condutividade elétrica. As maiores densidades foram verificadas entre os meses de outubro e janeiro, sugerindo ser este o principal período de reprodução da espécie. No entanto, larvas em estágio de pré-flexão e flexão também foram encontradas no inverno, possivelmente associadas às condições favoráveis para a reprodução. Indivíduos de todos os estágios estiveram presentes, ou seja, é provável que todo o ciclo de vida da espécie ocorra dentro da baía. A densidade de larvas mais desenvolvidas na superfície foi maior à noite, enquanto as larvas iniciais foram encontradas na superfície em ambos os horários, ou seja, o grau de desenvolvimento morfológico larval influencia no padrão de distribuição da espécie na coluna de água.
RESUMO
The aim of this study was to characterize the early development of Hoplias aff. malabaricus. The sampling was conducted during the period from November 1991 through February 1995, at 42 stations distributed in different environments of the upper Paraná river floodplain, Brazil. The specimens were taken from limnetic and littoral regions. Specimens were separated according to their development in larval (preflexion, flexion and postflexion stages) and juvenile periods. Morphometric and meristic variables were analyzed in 269 larvae and 74 juveniles (standard length ranging from 6.17 mm to 49.12 mm). Larvae showed fusiform body and intense pigmentation, a long intestine, large eyes and terminal mouth. Number of myomeres ranged from 37 to 45 (23-28 pre and 11-18 post-anal). The juveniles presented a body shape similar to their adults. The numbers of fin rays were: pectoral, 12; pelvic, 7-9; dorsal, 13-15; and anal, 10-12. Analysis of the growth showed metamorphosis in the early development of this species.
Este trabalho teve por objetivo caracterizar o desenvolvimento inicial de Hoplias aff. malabaricus. As amostragens foram realizadas entre novembro de 1991 e fevereiro de 1995, em 42 estações de coleta, distribuídas em vários ambientes da planície alagável do alto rio Paraná, Brasil. Para a obtenção do material, foram realizadas amostragens nas regiões pelágica (rede de plâncton) e litorânea (peneirão). Para a caracterização das diferentes fases, os indivíduos foram separados em períodos larval (estágios de pré-flexão, flexão e pós-flexão) e juvenil. Foram analisadas as variáveis morfométricas e merísticas em 269 larvas e 74 juvenis, com comprimento padrão variando entre 6,17 e 49,12 mm. As larvas apresentaram corpo fusiforme e altamente pigmentado, olhos grandes, intestino longo e boca terminal. O número total de miômeros variou de 37 a 45 (23 a 28 pré e 11 a 18 pós-anal). Os juvenis apresentaram a forma do corpo semelhante a do adulto. O número de raios das nadadeiras encontrado para a espécie foi: peitoral 12; pélvica 7-9; dorsal 13-15; e anal 10-12. A análise do crescimento indicou a metamorfose no início do desenvolvimento desta espécie.