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 Cuiaba 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 1.68 mm, 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.
Highlights
The greatest difficulty inherent to the study of freshwater ichthyoplankton is properly identifying fish eggs and larvae in their natural environments
Fish from this family exhibit parental care and are divided into two groups: substrate spawners, which attach their eggs to a substrate and exhibit parental care by both parents, and mouth-brooders, which carry their offspring in their mouths (Ribbink, 1990)
For the variables related to standard length (SL), the results indicated that head length (HL), body height (BH) and the Snout-pectoral fin distance (SPcF), SP1F, and SAF distances showed discontinuous isometric growth during development (Table 4 and Appendix)
Summary
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). Cichlidae is the second largest of the 160 characterized families within the order Perciformes, and it is composed of nearly 1 300 species worldwide and approximately 291 in South America alone (Kullander, 1998) Fish from this family exhibit parental care (generally performed by the female) and are divided into two groups: substrate spawners, which attach their eggs to a substrate and exhibit parental care by both parents, and mouth-brooders, which carry their offspring in their mouths (Ribbink, 1990). The aims of this study were to (i) morphologically describe the early stages (eggs, larvae and juveniles) of S. pappaterra using morphometric and meristic traits and (ii) assess changes in the growth rates throughout larval and juvenile development by analyzing the relationships between various morphometric traits using analytical regression models
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