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Reproductive biology of Steindachnerina insculpta (Fernandez-Yépez) (Teleostei, Curimatidae) in Furnas reservoir, Minas Gerais, Brazil

Biologia reprodutiva de Steindachnerina insculpta (Fernandez-Yépez) (Teleostei, Curimatidae) no reservatório de Furnas, Minas Gerais, Brasil

Abstracts

The 'saguiru' Steindachnerina insculpta, a small teleost detritivorous fish species in Furnas reservoir, upper rio Paraná basin, Minas Gerais, Brazil, has a prolonged period of reproductive activity that extends from September to March, with fractionated spawning. During gonadal maturation, the females showed a low hepatosomatic index, suggesting that hepatic substances are possibly transferred from liver to ovaries. During the reproductive period, this fish had lower stomach repletion and coelomic fat indexes, indicating that the species eat less and consume more fat reserves. The weight of the ovaries influenced positively the condition factor (K1), since the lowest K2 values (without the gonads weight), were obtained during maturation, confirming the influence of the weight of the ovaries upon the physiological condition of the females.

Freshwater teleost fish; reproduction; spawning


O 'saguiru' Steindachnerina insculpta, peixe teleósteo detritívoro que ocorre no reservatório de Furnas, bacia do alto Paraná, Minas Gerais, apresenta período reprodutivo prolongado que se estende de setembro a março, com desova parcelada. Durante a maturação gonadal, fêmeas apresentaram baixos valores do índice hepatossomático, sugerindo que possivelmente, substâncias hepáticas são transferidas do fígado para os ovários. Durante o período reprodutivo, os peixes desta espécie apresentam índices de repleção estomacal e de gordura celômica baixos, indicando diminuição da atividade alimentar e consumo de reservas. O peso dos ovários influencia positivamente o fator de condição (K1), uma vez que os mais baixos valores de K2 (sem o peso das gônadas) foram obtidos durante a maturação, confirmando a influência do peso dos ovários na condição fisiológica das fêmeas.

Desova; reprodução; teleósteo de água doce


Reproductive biology of Steindachnerina insculpta (Fernandez-Yépez) (Teleostei, Curimatidae) in Furnas reservoir, Minas Gerais, Brazil

Biologia reprodutiva de Steindachnerina insculpta (Fernandez-Yépez) (Teleostei, Curimatidae) no reservatório de Furnas, Minas Gerais, Brasil

Vinicius M. A. Ribeiro; Gilmar B. Santos; Nilo Bazzoli

Programa de Pós-graduação em Zoologia de Vertebrados, Universidade Católica de Minas Gerais. Rua Dom José Gaspar 500, 30535-610 Belo Horizonte, Minas Gerais, Brasil

ABSTRACT

The 'saguiru' Steindachnerina insculpta, a small teleost detritivorous fish species in Furnas reservoir, upper rio Paraná basin, Minas Gerais, Brazil, has a prolonged period of reproductive activity that extends from September to March, with fractionated spawning. During gonadal maturation, the females showed a low hepatosomatic index, suggesting that hepatic substances are possibly transferred from liver to ovaries. During the reproductive period, this fish had lower stomach repletion and coelomic fat indexes, indicating that the species eat less and consume more fat reserves. The weight of the ovaries influenced positively the condition factor (K1), since the lowest K2 values (without the gonads weight), were obtained during maturation, confirming the influence of the weight of the ovaries upon the physiological condition of the females.

Key words: Freshwater teleost fish; reproduction; spawning,.

RESUMO

O 'saguiru' Steindachnerina insculpta, peixe teleósteo detritívoro que ocorre no reservatório de Furnas, bacia do alto Paraná, Minas Gerais, apresenta período reprodutivo prolongado que se estende de setembro a março, com desova parcelada. Durante a maturação gonadal, fêmeas apresentaram baixos valores do índice hepatossomático, sugerindo que possivelmente, substâncias hepáticas são transferidas do fígado para os ovários. Durante o período reprodutivo, os peixes desta espécie apresentam índices de repleção estomacal e de gordura celômica baixos, indicando diminuição da atividade alimentar e consumo de reservas. O peso dos ovários influencia positivamente o fator de condição (K1), uma vez que os mais baixos valores de K2 (sem o peso das gônadas) foram obtidos durante a maturação, confirmando a influência do peso dos ovários na condição fisiológica das fêmeas.

Palavras-chave: Desova; reprodução; teleósteo de água doce.

Furnas reservoir was built in 1962 by damming the Grande River. It has 1522 km2 of maximum flooding area, a depth of 15.4 m and 20.86 x 109 m3 of water volume. The reservoir has a dendritic shape and a fish fauna in which small and medium-sized species are dominant (SANTOS & FORMAGIO 2000).

The 'saguiru' Steindachnerina insculpta (Fernandez-Yépez, 1948), a small detritivorous fish species, has its geographic distribution in the upper Paraná river basin, South America and it is important to the food chain maintenance (REIS et al. 2003). The species has an illiophagus feeding habit reaching a maximum total length of 15 cm for males and 21 cm for females in the Mogi Guassu river (GODOY 1975). There are few studies related to this species, included those concerning gillnet selectivity evaluations in Ibitinga reservoir, Tietê river (CAMPOS et al. 1991), and the determination of the spawning areas and period in Itaipu reservoir, upper Paraná river basin (BENEDITO-CECÍLIO & AGOSTINHO 1997).

The reproductive cycle is an important parameter in understanding the reproduction of native fish species and to the establishment of conservation programs (VAZZOLER 1996). The oocytes released by the females in the reproductive period may be total or fractioned. In tropical environments, total spawning usually occurs in large fish species that migrate over long distances and reproduce, usually in markedly seasonal lotic environments. Fractioned spawning, on the other hand, is frequent in fish living in stable, lentic environments being associated with reduced body size and relatively small ovaries of these species (NIKOLSKI 1963). Fractioned spawning is characterized by asynchronous oocyte development, long period of reproduction and high frequency of females with partially spawned ovaries (RINCHARD & KESTEMONT 1996). It constitutes a reproductive strategy designed to reduce the egg and larvae predation, the risk of spawning in unfavorable hydrographic and climatic conditions, and the competition for spawning sites (MCEVOY & MCEVOY 1992).

The fish energetic needs, which increase during gonadal maturation to meet the different reproductive strategies, are reduced in the period that precedes spawning and spermiation. Feeding is interrupted and endogenous nutrients are converted into energy for reproduction, with a consequent reduction in body weight and energetic reserves (MADDOCK & BURTON 1999). In tropical environments feeding plays a fundamental role in determining reproductive rhythm (VAZZOLER & MENEZES 1992). Variations in fish coelomic fat level (CFI) may be related to their reproductive cycle as well as the river or reservoir hydrologic cycle (LAMAS & GODINHO 1996). During the reproductive cycle, the condition factor (K) may vary according to the feeding conditions and gonadal development and may be used, for some species, as an indicator of spawning period (BARBIERI & VERANI 1987).

The present work focuses on the reproductive biology of S. insculpta in Furnas reservoir by determining the reproductive cycle stages, reproductive period length, type of spawning and the biological indexes related to the species reproduction.

MATERIALS AND METHODS

Two hundred and fifty males and five hundred and eleven females were captured in the Furnas reservoir, Minas Gerais State, Brazil (20º40'S, 46º19'W) from September 1992 to August 1994, using gill nets. All captured specimens were fixed in 10% formalin solution. After dissection, sex identification, and macroscopic determination of the stages of the reproductive cycle, the following data were recorded for each specimen: standard length (SL), body (BW), gonads (GW), liver (LW), stomach (SW), and coelomic fat (CFW) weights. The biometric data obtained were used for calculating the gonadosomatic (GW/BW x 100), hepatosomatic (LW/BW x 100), stomach repletion (SW/BW x 100) and coelomic fat (CFW/BW x 100) indexes, as well as the condition factors (K1 = BW/SL3; K2 = BW-GW/SL3). The stages of the reproductive cycle were established using the macroscopic characteristics of the gonads, whereas the spawning type was determined by analysis of the frequency distribution of the referred stages (BAZZOLI 2003). Data were analyzed quarterly according to the season of the year. An ANOVA test was performed for testing variations in the mean values of the indexes calculated for each stage of reproductive cycle and by sex. When needed, a Duncan's test was applied for determining statistically significant differences (p < 0.05) (SAMPAIO 1998).

RESULTS

The testes and ovaries of S. insculpta are elongated, paired organs, located latero-dorsally in the coelomic cavity and ventro-laterally to the gaseous bladder. They were attached to the coelomic wall and to the gaseous bladder by the mesorchium and mesovarium, respectively. Both testes and ovaries are joined in their caudal ends, forming the common duct that opens in the urogenital papilla. Variations in thickness, volume and color of the gonads were observed in the distinct stages of the reproductive cycle. Based on the variations in color, vascularization, volume, and turgidity, the following stages of the reproductive cycle of S. insculpta were determined: 1 = rest, 2 = initial ripening, 3 = advanced ripening/mature, 4A = partially spent for males and partially spawned for females, and 4B = totally spent for males and totally spawned for females (Tab. I). Over most of the study period, there was low occurrence of males and females in the rest stage. Males and females in the initial ripening and mature stages occurred practically in all trimesters of the two years studied, with a higher frequency of mature specimens in December-January-February. Spent/spawned males and females also occurred in almost all quarters sampled, but were found more frequently in March-April-May and June-July-August (Fig. 1).


The high frequency of partially spawned females in the two studied cycles, with occurrence of the extended reproductive period from September to March (Fig. 1), accompanied by quarterly variations in the gonadosomatic index, indicate that S. insculpta has a fractionated type spawning. The mean gonadosomatic index for males and females increased significantly (p < 0.05) from stage 1 to stage 3 and decreased thereafter (p < 0.05) (Tabs II, III ). The mean hepatosomatic index for females increased from stage 1 to stage 2 and decreased abruptly in stage 3 (p < 0.05). The mean stomach repletion index was significantly lower in stage 3, for males and females (p < 0.05). The mean coelomic fat index did not show statistically significant differences. The mean of the condition factors (K1 and K2) values for males did not show statistically significant differences during the reproductive cycle. For females, the K1 values were significantly higher in stage 3 (Tabs II, III ).

DISCUSSION

Ovaries and testes of S. insculpta are paired, elongated and fusiforms organs located in the coelomic cavity, ventrally to the kidneys, dorsally to the digestive tube and latero-ventrally attached to the gas bladder, similar to those found in other Brazilian Curimatidae (ALVES & GODINHO 1992, ALVARENGA et al. 2006).

In all quarters studied, males and females in reproductive activity and having fractionated-type spawning were recorded. An extended reproductive period and a fractionated spawning type appear to be characteristic for the most of Curimatidae (ROMAGOSA et al. 1984, ALVES & GODINHO 1992, HARTZ & BARBIERI 1994). However, Curimatella lepidura (Eigenmann & Eigenmann, 1889) has a total spawning type (ALVARENGA et al. 2006). The prolonged reproductive period, common in several Brazilian teleosts, occurs as a response to the conditions in tropical waters (LOWE-MCCONNELL 1987).

In this work, the variations in the GSI of males were more discreet, if compared to those of the females, and can be attributed to the differences between testes and ovaries (in terms of volume, mass and energetic demand required for the production of gametes). These results are similar to the findings of SLOTTE (1999) who also correlated GSI increasing with the lowering of the mesenteric fat at higher rates in females than in males.

The GSI and HSI of S. insculpta showed an inverse relation over the reproductive cycle, similarly to what was reported by YONEDA et al. (1998), HOJO et al. (2004), MAGALHÃES et al. (2004) and ALVARENGA et al. (2006). The HSI of females reached higher values, when compared with those of males, and felt abruptly during the advanced ripening/mature stage, at which time the GSI became higher, indicating the consumption of hepatic reserves during ovarian maturation. This occurs as a result of depletion of the storage of glycogen and lipids of hepatocytes (SVEDÄNG & WICKSTRÖM 1997), vitellogenin synthesis and transfer to the oocytes (LUZZANA et al. 1996). The HSI may also vary between teleosts species, due to the differences in energetic reserve storage capacity, physiological condition, feeding habits, and availability of nutrients in the habitat (SVEDÄNG & WICKSTRÖM 1997). Therefore, variations in the relation between GSI and HSI are attributable not only to gonadal maturation, but also to the physiological and adaptational capacity of each species, as well as to environmental conditions.

Both males and females showed lower SRI values in the advanced ripening/mature stage. The reduction in the feeding activity during the reproductive period is due to compression of the digestive organs by the gonads, particularly in females, with feeding being resumed immediately after spawning (SLOTTE 1999), as was observed in the present study. In the same way, in C. lepidura of the Juramento reservoir, Minas Gerais, Brazil, the stomach repletion was higher in the dry season, when fish are not in the reproduction season (ALVARENGA et al. 2006).

The CFI values of males and females were lower in the partially spent and totally spawned stages, respectively, pointing to the consumption of lipids during spermiation and ovulation, even though no significant differences were recorded in the CFI of females. Differences in CFI values between males and females showed by teleosts during the reproductive cycle can be attributed to the conversion of fat reserves into products needed for gonadal maturation, since only in females the metabolism of lipids is naturally accelerated by large quantities of ovarian steroids (RAJASILTA et al. 1997).

In males of S. insculpta, discreet variations of K1 and K2 were recorded over the reproductive cycle. In females, the highest K1 as well as the lowest K2 values were obtained during maturation confirming the influence of the weight of the ovaries upon the physiological condition of the females, as was observed in Steindachnerina elegans (Steindachner, 1874) by ALVES & GODINHO (1992).

In conclusion, S. insculpta spawned almost throughout the year in the Furnas Reservoir. The species showed fractionated spawning with peaks of advanced maturation/mature from December to February. During the reproductive period the species eat less and consume more fat reserves. In females, the weight of the ovaries influenced the condition factor and hepatic substances were transferred from liver to ovaries during gonadal maturation.

ACKNOWLEDGMENTS

To Furnas Hydrobiology and Hatchery Station (Furnas Centrais Elétricas S/A) staff for the assistance during the collection of fish, to the Brazilian Research Foundations: CNPq, FAPEMIG and FIP-PUC-Minas for the financial support and Robert J. Young for the suggestions on the English version.

Received in 29.III.2006; accepted in 26.II.2007.

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Publication Dates

  • Publication in this collection
    24 Apr 2007
  • Date of issue
    Mar 2007

History

  • Received
    29 Mar 2006
  • Accepted
    26 Feb 2007
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