Gilmar B. Santos

Reproductive biology of Moenkhausia intermedia (Eigenmann) (Pisces, Characiformes) in Itumbiara Reservoir, Goiás, Brazil

To study the reproductive biology of Moenkhausia intermedia (Eigenmann, 1908) in Itumbiara reservoir, Paranaiba river, Goias, Brazil, a total of 301 specimens (237 females and 64 males) were captured quaterly from January to December 1993. The gonadosomatic index of females and males were related to morphologic variations of the gonads in different reproductive cycle stages (RCS). Analysis of RCS frequency and variations in the gonadosomatic index showed that M. intermedia reproduces during the whole year with fractional spawning. The smallest standard length at advanced maturity stage was estimated as 6.6 cm for females and 6.0 cm for males. The stomach repletion and coelomic fat indexes of both sexes reached peak values in the rest stage, suggesting that this species probably store energy in this phase and consume its fat reserve during reproduction. In the Itumbiara reservoir there was female predominance (4:1). Males were smaller than females, indicating sexual dimorphism in M. intermedia.

Reproductive biology and feeding of Curimatella lepidura (Eigenmann & Eigenmann) (Pisces, Curimatidae) in Juramento reservoir, Minas Gerais, Brazil

Reproductive biology and feeding of Curimatella lepidura (Eigenmann & Eigenmann, 1889) were studied in Juramento reservoir, Sao Francisco River basin, Southeastern Brazil. Histological analyses and gonadosomatic indexes revealed females and males in reproductive activity from October to March and total spawning occurring from January to March coupled with the peak of spermiating males. In the dry season, the fishes accumulated energetic reserves for reproduction during a short rainy season. The species presented sexual dimorphism, being females larger than males and sexual maturation occurring close to 7.7 cm standard length for females and 7.1 cm for males. C. lepidura presented iliophagous feeding habit, ingesting mainly sediment/detritus and a small amount of acari, algae, Tricoptera insects and Ostracoda crustaceans, suggesting a probable role in nutrient recycling of the Juramento reservoir.

Reproduction of the catfish Iheringichthys labrosus (Lütken) (Pisces, Siluriformes) in Furnas reservoir, Minas Gerais, Brazil

The reproductive biology of Iheringichthys labrosus (Lutken, 1874) was studied in Furnas reservoir, Minas Gerais, Brazil. The fishes, 323 males and 817 females, were captured bimonthly from August 1993 to July 1994 by using gill nets with 3-10 cm mesh size. Gonadal maturation of the specimens was analyzed through macro and microscopical characteristics of the gonads. The secretory activity of the tubules of the caudal region of the testis was analyzed during the maturational testicular cycle. Females and males were in reproductive activity throughout the year in the reservoir. The peak of advanced maturation/mature stages occurred from October to January and of spawned/spent from February to May. The spawning of I. labrosus was identified as fractional or multiple type: occurring in the reservoir or in tributaries around it. The oocyte development of the species was asynchronous as different clusters of oocytes occurred simultaneously in the ovarian parenchyma. The epithelium of the tubules of the caudal region of the testis was in high secretory activity during advanced maturation/mature stage and this activity was absence in resting. The gonadosomatic index followed gonadal maturation, and the hepatosomatic index of females was lowest in advanced maturation/mature probably due the contribution of the liver in the vitellogenesis. The variations of the stomach repletion index, coelomic fat and condition factor indicated that the feeding activity was reduced and that the energetic reserves were consumed during the reproductive period.

Reproductive biology of the peacock bass Cichla piquiti (Perciformes: Cichlidae), an exotic species in a Neotropical reservoir

Para analisar a biologia reprodutiva do tucunare Cichla piquiti foram coletados bimestralmente 361 exemplares no reservatorio de Itumbiara, sudeste do Brasil, no periodo de dezembro/2004 a novembro/2005. Machos e femeas em atividade reprodutiva ocorreram durante quase todo ano, com pico reprodutivo antes do inicio das chuvas, quando a temperatura da agua permanecia ainda baixa, indicando que estas variaveis ambientais nao influenciaram diretamente na reproducao de C. piquiti. O longo periodo reprodutivo, ovarios parcialmente desovados contendo foliculos pos-ovulatorios e ovocitos em todos os estadios de desenvolvimento, indicaram desenvolvimento assincronico dos ovocitos e desova multipla. A media de comprimento total e peso corporal foram, respectivamente, 38,2 ± 7,0 cm e 965,0 ± 654,0 g para machos e 37,4 ± 6,1 cm e 899,0 ± 495,0 g para femeas, estatisticamente nao mostrando dimorfismo sexual em tamanho. Os menores exemplares, macho e femea, capturados no estadio de maturacao avancada mediram 31,0 cm e 29,0 cm de comprimento total, respectivamente. O fator de condicao (K) de machos e femeas nao apresentou diferencas significativas durante o ciclo reprodutivo e o coeficiente angular (b) da relacao peso-comprimento foi 3,22, sugerindo que a reproducao e o ciclo hidrologico anual nao interferem na condicao de saude. Cichla piquiti e um peixe piscivoro exotico que esta bem adaptado a este reservatorio neotropical, o qual exibe condicoes ambientais consideravelmente diferentes de seu habitat original. Este estudo indica que a especie apresenta plasticidade na reproducao e na alocacao de recursos, provavelmente devido a nao sazonalidade do reservatorio e a exploracao das especies nativas

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

The ‘saguiru’ Steindachnerina insculpta , a small teleost detritivorous fish species in Furnas reservoir, upper rio Parana 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.

Reproductive biology of Leporinus taeniatus Lütken (Pisces, Anostomidae) in Juramento Reservoir, São Francisco River basin, Minas Gerais, Brazil

A biologia reprodutiva do piau-jejo Leporinus taeniatus Lutken, 1875, especie endemica da bacia do rio Sao Francisco, foi estudada utilizando-se tecnicas biometricas, macroscopicas e microscopicas. Capturaram-se no reservatorio de Juramento, MG, em coletas trimestrais, 121 machos e 94 femeas, no periodo de marco de 2002 a fevereiro de 2003. Observou-se que femeas sao maiores do que os machos indicando dimorfismo sexual. Determinaram-se os estadios de maturacao gonadal atraves de analise histologica e do indice gonado-somatico. Os picos de maturacao/maduro e de peixes desovados/espermiados ocorreram no trimestre dezembro/janeiro/fevereiro. L. taeniatus apresentou desova total e desenvolvimento grupo-sincronico dos ovocitos. O indice gonadossomatico acompanhou a maturacao das gonadas e o indice de gordura celomica apresentou menores valores no estadio maturacao/maduro, indicando consumo de reservas graxas no periodo reprodutivo. O indice de replecao estomacal apresentou maiores valores no estadio desovado/espermiado, indicando que a especie alimenta-se mais apos a reproducao.

Gonadal structure and gametogenesis of Loricaria lentiginosa Isbrücker (Pisces, Teleostei, Siluriformes)

The gonadal structure and gametogenesis of Loricaria lentiginosa Isbrucker, 1979 were studied through anatomical and histological techniques. Forty two males and ten females in maturation/mature stage were captured in the reservoir of Porto Colombia, Parana river basin, Minas Gerais, using gill nets, from November 2001 to October 2002 (tri-monthly captures). Examination of the testes revealed that they were paired, elongated and not fringed organs. Histologically, the testes presented three distinct regions: cranial espermatogenic; transistion espermatogenic and secretory; and caudal exclusively secretory. Standard histochemical techniques detected neutral glycoproteins from the secretion of the tubules of the caudal region. Espermatogenesis occurred in cysts throughout the whole extension of the wall of the seminiferous tubules, which anastomosis themselves and liberated the spermatozoa into the lumen of the espermatic ducts. The ovaries were paired, saculiformes and, histologically, they presented ovigerous lamellae that contained the cells of ovogenic ancestry. The oocytes were classified into four stages, based on their cytological characteristics and the cell layers that surrounded them. Post-ovulatory follicles and vitelogenic oocytes in the follicular atresia process also were observed.

DNA barcoding and morphological identification of neotropical ichthyoplankton from the Upper Paraná and São Francisco

The identification of fish larvae from two neotropical hydrographic basins using traditional morphological taxonomy and DNA barcoding revealed no conflicting results between the morphological and barcode identification of larvae. A lower rate (25%) of correct morphological identification of eggs as belonging to migratory or non-migratory species was achieved. Accurate identification of ichthyoplankton by DNA barcoding is an important tool for fish reproductive behaviour studies, correct estimation of biodiversity by detecting eggs from rare species, as well as defining environmental and management strategies for fish conservation in the neotropics.

Ecological assessment of a southeastern Brazil reservoir

Reservoirs are artificial ecosystems with multiple functions having direct and indirect benefits to humans; however, they also cause ecological changes and influence the composition and structure of aquatic biota. Our objectives were to: (1) assess the environmental condition of Nova Ponte Reservoir, Minas Gerais state, southeastern Brazil; and (2) determine how the aquatic biota respond to disturbances. A total of 40 sites in the littoral zone of the reservoir were sampled to characterize physical and chemical habitat, land use, and benthic macroinvertebrate and fish assemblages. The predominant type of land cover near the reservoir was natural vegetation. A total of 29 fish species and 39 macroinvertebrate taxa were collected, including eight alien species. Most sites had intermediate levels of human disturbance, however, high levels of degradation were associated with high proportions of alien species. Disturbances at multiple scales may alter natural patterns and processes, leading to environmental changes and damaging biological communities. Our results reinforce the importance of assessing reservoir ecological conditions at several scales. The study of land use, littoral zone physical habitat characteristics, water quality, and assemblage structure set the ground for proposing actions to rehabilitate and conserve aquatic ecosystems.

Observations on the seasonal breeding biology and fine structure of the egg surface in the white piranha Serrasalmus brandtii from the São Francisco River basin, Brazil

In the Juramento Reservoir, south-eastern Brazil, the white piranha Serrasalmus brandtii showed a prolonged reproductive season, with evidence for multiple spawning and a reproductive peak associated with seasonal rains. The egg surface exhibited a honeycomb-like pore canal arrangement and an adhesive apparatus surrounding the micropyle. Electron microscopic analysis suggests a role for the micropylar cell and neighbouring follicular cells in secretion of substances for egg attachment.