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Piranha Eggs - Serrasalmus spilopleura (= S. maculatus)

with additional information on Larvae and Juveniles:  S. spilopleura v. S. marginatus.

Frank Magallanes - March 12, 2004

 

Science has been studying fish eggs for at least a century, probably longer. China certainly has the historical knowledge of studying carp eggs as does Medieval Europe. In those studies up to the present it is well known that higher temperatures decreases the time for eggs to hatch. Smaller eggs also take less time to develop than larger eggs (Pauly, D. and Pullin, R. S. V. 1988).  Characin eggs have been studied for a number of years by science. This study includes the piranhas and pirambebas. Recently, Quagio-Grassiotto and A. C. D. Guimaraes (2003) discovered the morphology of S. spilopleura (= S. maculatus) and its egg envelope. The species eggs not only reflects its oviparous nature, but also its eggs are adhesive. The oocytes layer (acellular layer) is formed by proteins and polysaccharides. This portion is known as the zona radiata, zona pellucida, chorinic vitelline envelope, chorion, vitellinic membrane, or egg envelope. Oviparous species like S. spilopleura, the egg is structured by primary and secondary envelopes. Much of its creation is by evolutionary trends, adaptional processes, and environmental conditions (Ivankov and Kurdyayeva 1973; Nagahama 1983; Yamagami et al. 1992).

 

In the subfamily Serrasalminae, which includes the piranhas and pirambebas, genera Pygocentrus, Serrasalmus, Pristobrycon and Pygopristis, the group have a long reproductive period during the raining season (Rodrguez et al., 1978; Leao et al, 1991; Vazzoler and Menezes 1992; Ferreria et al. 1996). Serrasalmus spilopleura, reproduction is continuous, with multiple spawnings (Lamas and Godinho 1996). In this study, adult female specimens of S. spilopleura were caught and collected monthly from the Jurumirim reservoir, Alto Paranapanema River, Sao Paulo State, Brazil from March 1998 to February 1999. The specimens were anaesthetized and their gonads were removed, cut into small segments, and fixed overnight in paraformaldehyde and gluaradehyde in Sorensen phosphate buffer. The ovulated eggs were removed from the ovarian cavity and fixed the same way. Sections of prepared ovary and ovulated eggs were examined and photographed using an electron microscope.

 

Below, is the abstract on this study:

 

Abstract

 

Quagio-Grassiotto, I. and Guimarães, A. C. D. 2003. Follicular epithelium, theca and egg envelope formation in Serrasalmus spilopleura (Teleostei, Characiformes, Characidae). Acta Zoologica (Stockholm) 84: 121.

 

The follicular epithelium and theca of oocytes in Serrasalmus spilopleura differentiates during the initial primary growth phase. The follicular cells are squamous and the thecal cells are disposed in two layers. During the secondary growth phase, follicular cells become cuboidal, acquire characteristics typical of protein- or glycoprotein-producing cells, and show dilated intercellular spaces. Formation of the egg envelope in S. spilopleura begins in the previtellogenic oocytes as a layer of amorphous electron-dense material is laid down on the oolemma. During vitellogenesis, another layer of electron-dense material appears beneath the first layer. Also during this phase, a layer of amorphous, less electron-dense material is formed adjacent to the follicular epithelium. The secondary egg envelope appears at the postvitellogenic phase and is composed of a filamentous and undulant material. The morphology of the egg envelopes in S. spilopleura reflects not only its oviparous nature but also the fact that its eggs are adhesive.

 

S. spilopleura, the thickness of the eggs and the primary envelope is involved in the process of fertilization. This protects the integrity of the egg until the embryo has completely developed (Yamagami et al. 1992). This thickness of the egg is related to different reproductive strategies. Therefore, the egg thickness is subject to heavy mechanical stress than in buoyant eggs or those laid in sheltered areas (Ivankov and Kurdyayeva 1973). S. spilopleura shows an inherent thickness in its primary envelope which is likely related to is oviparous nature.

 

Like other Serrasalminae, their eggs are laid on submerged marginal vegetation (Cutright 1942). In the work, Adhesiveness and surface patterns of eggs in neotropical freshwater teleosts (Rizzo, Sato, Barreto, and Godinho, 2002) the eggs of S. spilopleura were found to be honeycomb-like pores. This special arrangement of the outer zona radiata was wider than those other species examined in this study. S. spilopleura eggs were found to be polygonal in shape and organized in a honeycomb fashion. Of special interest the mycropylar disc of S. spilopleura resembled the adhesive disc of Pygocentrus nattereri (Wirz-Hlavacek & Riehl, 1990). In S. spilopleura this apparatus does not contain filaments. 

 

 

Despite the the absence of data that elucidate the mechanism by which eggs of these species adhere to substrata, it could be postulated that the micropylar disc may play a role in adhesiveness. Since the micropyle in these fishes is located in the center of the micropylar disc, synchronization of male and female spawning behavior is of striking importance (Riehl & Appelbaum, 1991). In this case, the eggs should be fertilized before they attach to the substratum as in P. nattereri. In conclusion, the egg surface pattern is related to the degree of egg adhesiveness and is the same at the gender level in Characiformes; on the other hand, there is a strong correlation between jelly coat and Siluriformes eggs, apparently without a relationship between structure and adhesiveness.

 

Another aspect is the morphometric variation of larvae and juveniles of Serrasalmus spilopleura (= S. maculatus) and S. marginatus of the Paraná basin, Brazil. Maristela Cavicchioli, Keshiyu Nakatani and Oscar Akio Shibatta (1997). The larvae and juveniles of Serrasalmus spilopleura and S. marginatus of the upper Paraná river floodplains are described. The character that distinguishes the species in the early stages of larval development in the number of myomeres: 32-35 (mean 34.56) for S. spilopleura and 36-39 (37.01) for S. marginatus. The shape of the snout, the postmedian region, and the caudal peduncle were determinant in the separation of the species in the flexion and principal  components analysis, allied to the geometrical method of shape analysis, discriminated morphometrically  the species at all developmental stages. The length of the snout and the distances related to the postmedian region and caudal peduncle distinguished the species in all the series of landmarks and were, therefore, fundamental discriminating variables for the larval stages and juvenile period.

 

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