Marco Aurélio Azevedo

Reproductive Biology of the Inseminating Glandulocaudine Diapoma speculiferum Cope (Teleostei: Characidae)

Abstract The reproductive period of the inseminating glandulocaudine Diapoma speculiferum was determined through the analysis of 133 males and 158 females obtained from monthly collections in Rio Grande do Sul, Brazil. The reproductive period is highly seasonal, occurring from September to February, which corresponds to the Austral spring and summer. Both male and female gonadosomatic indices were highly correlated with changes in water temperature and day length and, to a lesser extent, food availability. No correlation with rainfall was found. Absolute fecundity (mean 491.1 ± 159.5 oocytes per female) was similar to those found in two externally fertilizing cheirodontine characids but lower than that found in the inseminating glandulocaudine Pseudocorynopoma doriae. Relative fecundities (oocyte number per milligram total body weight) of the inseminating D. speculiferum and P. doriae were found to be lower than that of two externally fertilizing cheirodontines, suggesting that inseminating species may expend a smaller amount of energy in egg production, perhaps as a result of a higher efficiency in fertilization. Gonad histology showed the presence of spermatozoa in ovaries of maturing females, indicating that courtship and insemination take place before the ovaries are mature. Fertilized eggs were not found in the ovaries, suggesting that fertilization may be a very rapid event once oocytes are ovulated. O período reprodutivo do glandulocaudíneo com inseminação, Diapoma speculiferum, foi determinado pela análise de 133 machos e 158 fêmeas obtidos em coletas mensais no Rio Grande do Sul, Brasil. Seu ciclo reprodutivo é sazonal ocorrendo de setembro a fevereiro, correspondendo á primavera e verão na região Austral. Para machos e fêmeas o índice gonadossomático foi altamente correlacionado com as mudanças na temperatura da água e fotoperíodo e, em menor extensão, com a disponibilidade de alimento. Quanto ao índice pluviométrico, não foi verificada nenhuma correlação. A média da fecundidade absoluta (491,1 ± 159,5 ovócitos por fêmea) foi semelhante a observada em dois queirodontíneos de fecundação externa, e menor do que o glandulocaudíneo com inseminação Pseudocorynopoma doriae. A fecundidade relativa (número de ovócitos por miligrama de peso total) dos glandulocaudíneos com inseminação D. speculiferum e P. doriae foi menor do que nos queirodontíneos com fertilização externa, sugerindo que espécies com inseminação tem um menor gasto energético na produção dos ovócitos, talvez como resultado de uma maior eficiência na fertilização. A histologia das gônadas demonstrou a presença de espermatozóides em ovários de fêmeas em maturação, indicando que a corte e inseminação iniciam antes dos ovários estarem maduros. Não foram encontrados ovos fertilizados nos ovários, sugerindo que a fertilização ocorra durante a ovulação.

Comparative dietary analysis of two populations of Mimagoniates rheocharis (Characidae: Glandulocaudinae) from two streams of Southern Brazil

The diet of two populations of Mimagoniates rheocharis, from two freshwater streams of the rio Tramandai, northeastern Rio Grande do Sul, Brazil, are described and compared. The specimens were collected monthly from January 1998 to March 1999, with dip nets and seine nets and preserved in 10% formalin. In laboratory, the standard length of each specimen was measured. The stomachs were removed and dissected for identification of the alimentary items. The data were analyzed using the frequency of occurrence, percent composition and index of alimentary importance methods, being the last two compared among different classes of standard length. Three methods of analysis showed the highest values for allochthonous insects, regardless the locality of collection or body size of the specimens.

Reproductive biology and development of gill glands in the inseminating characid, Macropsobrycon uruguayanae Eigenmann, 1915 (Cheirodontinae: Compsurini)

The reproductive biology and development of the gill gland are described for Macropsobrycon uruguayanae, an inseminating characid species of the tribe Compsurini, subfamily Cheirodontinae. Between April 2001 and March 2002, 117 males and 143 females of this species were collected in the rio Ibicui, Uruguay basin in the State of Rio Grande do Sul, Brazil. Reproductively active individuals were present during most months sampled, indicating lack of a well-defined seasonal reproductive period. Several maturing females were found to be inseminated before completing full maturation. Histological analyses demonstrated spermatozoa within the ovaries of females in different stages of gonadal maturation collected during most months. No immature females had inseminated ovaries. Standard length at first gonadal maturation was estimated to be 24 mm for both males and females. Mean absolute fecundity was 191.08 (± 48.83 SD) oocytes per female, one of the lowest among characids. Relative fecundity was 0.539 (± 0.069 SD) oocytes per mg weight of the female, a value similar to that found for the majority of species of Cheirodontinae. The presence of two cohorts of oocytes within ovaries of M. uruguayanae indicates synchronous development, with total spawning. The mean diameter of mature oocytes was 0.6711 (± 0.1252 SD) mm, smaller than that found for the majority of species of Characidae. Gill glands occurred in all mature males, as well as in males undergoing advanced maturation. In the latter case, fewer gill filaments comprised the glands. Gill glands were not observed in immature males, males undergoing the initial stages of maturation, or in any female. A given gill gland may comprise as many as 24 filaments of the lateral hemibranch of the first gill arch. Secondary lamellae within most of the gill gland are greatly reduced, with columnar cells being present between them. These columnar cells contain abundant vesicles, suggesting secretory activity. The morphology of the gill gland of M. uruguayanae resembles that found in the majority of characid species that possess this structure.

Reproductive biology of Bryconamericus stramineus Eigenmann, 1908 (Ostariophysi: Characidae) from the Rio Ibicuí, RS, Brazil

Reproduction of Bryconamericus stramineus was described based on the analysis of 208 females and 166 males collected monthly in the Rio Ibicui, from April 200 1 through March 2002. Reproduction occurred between September and December, with a lower peak in Februa ry. The mean absolute fecundity was 371.3 ( 244.6) oocytes and the mean relative fecundity was 0.35 ( 0.08) oocytes/mg of total weight and the fish was a multiple spawner. A weak correlation between GSI of males and day lengt h was observed. Other parameters (stomach repletion and hepatosomatic index, rainfall and temperature) did not show any correlation with GSI. However, some of these factors might act as “starters” of gonadal maturati on. The presence and frequency of fin ray hooks on the males was compared with the gonadal maturation stages, mo nths and standard length classes. Well-developed ho oks were found mainly in the mature males during the reprodu ctive period and in the largest individuals.

Reproductive characteristics of characid fish species (Teleostei, Characiformes) and their relationship with body size and phylogeny

In this study, I investigated the reproductive biology of fish species from the family Characidae of the order Characiformes. I also investigated the relationship between reproductive biology and body weight and interpreted this relationship in a phylogenetic context. The results of the present study contribute to the understanding of the evolution of the reproductive strategies present in the species of this family. Most larger characid species and other characiforms exhibit a reproductive pattern that is generally characterized by a short seasonal reproductive period that lasts one to three months, between September and April. This is accompanied by total spawning, an extremely high fecundity, and, in many species, a reproductive migration. Many species with lower fecundity exhibit some form of parental care. Although reduction in body size may represent an adaptive advantage, it may also require evolutionary responses to new biological problems that arise. In terms of reproduction, smaller species have a tendency to reduce the number of oocytes that they produce. Many small characids have a reproductive pattern similar to that of larger characiforms. On the other hand they may also exhibit a range of modifications that possibly relate to the decrease in body size and the consequent reduction in fecundity. Examples of changes in the general reproductive pattern include the following: reduction in the size of mature oocytes; increase in fecundity; production of several batches of oocytes; an extended reproductive period or even continuous reproduction that allows individuals to reproduce more than once a year; high growth rates; rapid recruitment of juveniles; presence of more than one reproductive cohort that increases the sexually active population; and multiple independent development of insemination as a reproductive strategy. These changes are possibly associated with adaptive pressures that are related to the reduction in body size. In addition, such reproductive characteristics or novelties may reflect the phylogenetic history of a given species.

Biologia reprodutiva de Astyanax henseli (Teleostei, Characidae) do curso superior do Rio dos Sinos, RS, Brasil

No presente estudo e descrita a biologia reprodutiva de uma populacao de Astyanax henseli Melo & Buckup, 2006 do curso superior do rio dos Sinos, Caraa, Rio Grande do Sul, Brasil. Foram analisados 336 exemplares, sendo 169 machos, 154 femeas e 13 cujo sexo nao foi possivel ser determinado. O periodo reprodutivo teve aproximadamente cinco meses de duracao, ocorrendo entre agosto e dezembro, com pico do indice gonadossomatico (IGS) em outubro, correspondendo ao final do inverno e a primavera no hemisferio sul. Nao houve correlacao estatisticamente significativa do IGS com os fatores abioticos (temperatura, precipitacao e fotoperiodo). No entanto, sugere-se que estes fatores estejam atuando como desencadeadores da maturacao gonadal. Fatores bioticos como o indice de replecao estomacal (IR) e indice hepatossomatico (IHS), tambem nao mostraram correlacao estatisticamente significativa com o IGS. Apesar disso, os valores de IR indicam que A. henseli continua se alimentando ativamente durante o periodo reprodutivo, enquanto que os baixos valores de IHS durante do pico reprodutivo sugerem um maior gasto das reservas hepaticas neste periodo. A proporcao sexual de 1:1 foi encontrada ao longo dos meses do ano, nas classes de comprimento e na populacao como um todo. O comprimento de primeira maturacao gonadal foi estabelecido em 69 mm para os machos e 60 mm para as femeas. A media da fecundidade absoluta foi de 3.038 ovocitos e a da fecundidade relativa 0,13 ovocitos mg-1. O desenvolvimento ovocitario indicou uma desova total.

Unique Derived Features in Spermiogenesis and Sperm Morphology Supporting a Close Relationship between the Species of Hollandichthys and Rachoviscus (Characiformes: Characidae)

Hollandichthys and Rachoviscus are endemic to the Atlantic coastal drainages of Brazil and have been historically hypothesized as related to different genera and even subfamilies of the Characidae. We describe the testis morphology, spermiogenesis, and sperm ultrastructure of species of both genera under light, transmission, and scanning electron microscopy, and provide unique characters that support a close relationship among Hollandichthys and Rachoviscus. The testes have a similar organization with a tripartite structure, showing a spermatogenic-cranial region, a differentiating-intermediate region, and a storage-caudal region that is continuous with the sperm duct. During spermiogenesis, the final spermatic differentiation occurs in the luminal compartment of the differentiating-intermediate region of the testis. This is herein termed as “partially cystic,” being distinct from that of any other characids previously described. At the beginning of spermiogenesis, the centriolar complex lies in a medial position in relation to the nucleus, the nucleus moves and slightly elongates toward the flagellar axis forming an eccentric nuclear fossa, and then the nucleus turns backward and elongates forward. The species of both Hollandichthys and Rachoviscus share the presence of long, spiraling mitochondria in the midpiece that seem to be unique among characids. Sperm competitiveness seems to be a determinant factor in accelerating the rate of phenotypic changes in nucleus length and sperm shape among inseminating characids. This is exemplified by the differences found in sperm nucleus shape and length between the two sister species of Rachoviscus, as well as between these species and their sister lineage (Hollandichthys). The formation of sperm packages was observed in Rachoviscus graciliceps. Hollandichthys e Rachoviscus são gêneros endêmicos das drenagens costeiras Atlânticas do Brasil e tem sido historicamente considerados como relacionados a gêneros e até mesmo subfamílias distintas de Characidae. A morfologia dos testículos, a espermiogênese e a ultraestrutura dos espermatozóides das espécies dos dois gêneros são descritas sob microscopia ótica e microscopia eletrônica de transmissão e varredura, fornecendo caracteres únicos que suportam uma relação próxima de parentesco. Os testículos apresentam uma organização semelhante em uma estrutura tripartite, com uma região espermatogênica-craniana, uma região de diferenciação intermediária e uma região caudal de armazenamento, que é contínua com o ducto espermático. Durante a espermiogênese, a diferenciação final do espermatozóide ocorre no compartimento luminal da região intermediária dos testículos, sendo aqui denominada de espermiogênese “parcialmente cística,” distinta de qualquer outra descrita anteriormente em Characidae. No início da espermiogênese, o complexo centriolar encontra-se em uma posição medial em relação ao núcleo, o núcleo se move e se alonga um pouco em direção ao eixo flagelar formando uma fossa nuclear excêntrica, e, em seguida, o núcleo retorna e se alonga para a frente. As espécies de Hollandichthys e Rachoviscus compartilham a presença de mitocôndrias espirais na peça intermediária, que parece ser única em Characidae. A competição do esperma parece ser um fator determinante na aceleração do ritmo das alterações fenotípicas de comprimento do núcleo e forma do espermatozóide entre os caracideos inseminadores, exemplificado pelas diferenças encontradas entre as duas espécies irmãs de Rachoviscus, bem como entre estas espécies e seu grupo irmão (Hollandichthys). A formação de feixes de espermatozóides foi observada em Rachoviscus graciliceps.

Reproductive strategies in two inseminating species of Glandulocaudini, Mimagoniates microlepis and Mimagoniates rheocharis (Characiformes: Characidae: Stevardiinae).

The reproductive biology of two inseminating Glandulocaudini species, Mimagoniates microlepis and Mimagoniates rheocharis, was investigated and compared with reproductive patterns described for other inseminating and non-inseminating characids, hypothesizing the evolutionary history of these reproductive traits. The long reproductive period, with higher activity in colder months, distinguishes the reproductive strategy of these species when compared with most characiforms. The M. rheocharis population was structured in two groups of males throughout the year, mature males with high gonado-somatic index (IG  = 2·0 and 4·4) and immature and maturing males with low IG values (0·0 and 1·2). Mimagoniates rheocharis and M. microlepis showed the lowest absolute mean fecundities known for characids, indicating that inseminating species allocate less energy to oocyte production and reinforcing the hypothesis that insemination has an adaptive advantage, which provides a higher chance of fertilization.

Reproductive traits of Gymnogeophagus labiatus (Teleostei, Cichlidae), in an upper stretch of Sinos river, Caraá, Brazil

This work describes the reproduction of Gymnogeophagus labiatus (Hensel, 1870) from an upper stretch of Sinos river, southern Brazil, based on the analysis of 174 males and 132 females captured in monthly samples taken from January to December 2007. Results showed that reproductive activity occur in spring and summer although ripe males were found along the year. The standard length of the smallest ripe male was 104.74 mm (Lt) and the smallest ripe female was 55.00 mm (Lt). There was a significant difference in total sex ratio, with 1.32 males to each female (χ2 = 5.76). Males were much more abundant in March (1.75 males: 1 female) and December (5 males: 1 female). Females were more abundant in the 62├77 mm interval (1 male: 2.36 female) while males were more abundant in the 77├92 mm size interval (2.57 males: 1 female). The largest length intervals were composed of only males. Mean absolute fecundity was 113.4 (± 31.24 sd) and mean relative fecundity was 0.0125 (± 0.0026 sd) oocytes/mg. In ripe ovaries, small-diameter oocytes were observed at high frequencies while larger ones occurred at lower frequencies. This pattern is common in fishes with asynchronous oocyte development. Characteristics of G. labiatus, such as low fecundity, asynchrony in oocyte development, multiple spawning, and its well-known parental care behavior, are consistent with an equilibrium strategy, as proposed for other cichlids.

Life history traits of Characidium pterostictum (Characiformes, Crenuchidae) along the longitudinal gradient of a Neotropical river in southern Brazil

Life history traits of Characidium pterostictum Gomes, 1947 (Characiformes, Crenuchidae) from three diff erent reaches of the upper Sinos river, southern Brazil, were described and comparatively analyzed according to the longitudinal gradient. For all reaches, results indicated a seasonal reproductive strategy with a higher intensity during warmer months of higher photoperiod (November to February). Only females were found in the upstream reach and they were more numerous than males in all the sampled reaches. Mean absolute fecundity ranged from 5,189 (±2,131 SD) to 7,394 (±3,807 SD), whereas mean relative fecundity (oocytes per mg of female total weight) ranged from 1.08 (±0.40 SD) to 1.12 (±0.29 SD). Oocyte development was characterized as synchronic in two groups, typical of total spawning. Longitudinal gradient comparison suggests that body size (standard length) of C. pterostictum individuals and sex ratio were the only characteristics that diff ered between sampled reaches. Larger individuals and thus females tended to be more frequently found in upstream reaches of the Sinos river, with a decrease in body size and in the proportional number of females towards downstream.