Abstract
Abstract Aim: To analyze temporal distribution of larvae and juveniles and the early development and of Moenkhausia cf. gracilima. Methods Samples were taken quarterly in twenty-five sites in the upper Paraná River floodplain between August 2013 and May 2015. The samples were taken under the water surface at night using 0.5 mm mesh plankton nets. In the laboratory, samples were sorted, identified and separated into larval (preflexion, flexion and postflexion) and juvenile periods. Results A total of 248 individuals was collected, mainly in the Saraiva Lagoon, suggesting that the entire life cycle of this species occurs in this environment. The reproductive period takes place between December and April, since the postflexion larvae were found until May. However, the occurrence of juveniles between February and May indicates probable batch spawning. Among the 95 individuals used for ontogenic description, 82 were larvae and 13 juveniles. Larvae may be characterized by irregular pigmentation in the upper region of the head, mouth, and body, increasing throughout development; upper lobe of the caudal fin more pigmented than the lower lobe, only visible in postflexion larvae; terminal mouth; anal opening located anterior to the median region of the body and total number of myomers ranging from 34 to 40 (15 to 20 pre and 16 to 23 postanal), while juveniles have characteristics similar to adults. The total number of fin rays is: P. 11-16, V. 7-11, D, 9-11 and A. 21-23. Conclusions According to the distribution of developmental periods it is possible to conclude that this species reproduces in the summer, preferably in lagoons. Growth analysis indicated important alterations in larval morphology (metamorphosis) that may be associated with the ecomorphological characteristics of the species. The morphological separation of larvae of M. cf. gracilima from other larvae of small characids, especially at preflexion and flexion stages may be complicated by the overlap of traits, suggesting the use of other variables, mainly morphometric, for the separation of the species.
Highlights
Preflexion larvae occurred only in February 2014, while flexion larvae corresponded to 5% and 8% of the samples taken in February 2014 and 2015, respectively
The type of reproductive strategy used by the parents, that is, from the way the egg is fertilized to the type of initial development directly conditions fish ontogeny (Balon, 1984)
Moenkhausia cf. gracilima presents this model of life cycle and its early development can be classified as indirect, with the presence of free-living organisms with different developmental stages (Miller & Kendall Junior, 2009)
Summary
Research on the ecology of fish eggs and larvae is of great importance to assist in the identification of spawning and nursery areas (Baumgartner et al, 2004; Bialetzki et al, 2005; Oliveira & Ferreira, 2008; Hermes-Silva et al, 2009), detection and evaluation of fish stocks and knowledge of population dynamics (Hempel, 1973; Agostinho et al, 2004), evaluation of the effects of different human interferences, such as pollution (Campagna et al, 2006), habitat Arrumado fragmentation (Sanches et al, 2006) and species introduction (Bialetzki et al, 2004, Kipper et al, 2011). There is still little known about fish larvae systematics and studies on egg systematics are lacking; only a few species have their early developmental stages known (Bialetzki et al, 2016). This difficulty is a consequence of the lack of comparative literature, high morphological similarity of the early stages between species, and a great difference in relation to the characteristics when compared to the adult (Snyder, 1981; Fuiman, 1983; Bialetzki et al, 1998). Among the groups present in samples collected in natural environments, considering the high morphological similarity, stand out the early stages of several species of the family Characidae. Ichthyoplankton surveys conducted in different environments of Paraná River by Castro et al (2002), Bialetzki et al (2005) and Ziober et al (2007) report a significant portion of the community classified in this family, mainly due to the difficulty of identification at lower taxonomic levels
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