Navegando por Autor "FONTOURA, Nelson Ferreira"

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Acesso aberto (Open Access)
Predicting size at first sexual maturity from length/weight relationship: a case study with an Amazonian catfish
(Universidade Federal do Pará, 2016) FREITAS, Tiago Magalhães da Silva; ALMEIDA, Vitor Hudson da Consolação; MONTAG, Luciano Fogaça de Assis; FONTOURA, Nelson Ferreira
Relationship between length and weight (LWR) is used to describe aspects concerning the life cycle of fish, but does not considers possible changes during the lifetime mainly due to the sexual maturation. Thus, this study aims to identify the size at first maturity of Auchenipterichthys longimanus (Siluriformes: Auchenipteridae) and infer if the reproductive engagement could change growth pattern, concerning the LWR. Estimates of the size at first maturity (L 50 ) were made by visual identification of gonadal development and through the gonadosomatic index (G SI ). L 50 was estimated as 12.5 cm for males and 13.0 cm for females when applied visual identification of gonads development. L 50 estimates increased to 13.05 cm for males and 13.7 cm for females when estimated from G SI values. LWR was adjusted by using a regular power function and through the polyphasic growth model, with proportionality and allometric coefficients changing in a two phases. The results indicate differences in the growth pattern concerning males and females, as well as polyphasic growth. The change in the growth pattern of the polyphasic LWR was estimated at 11.42 cm for males and 12.53 cm for females, suggesting that changes in the growth pattern can sign-out the attainment maturity in this catfish.
Acesso aberto (Open Access)
Reproductive characteristics and the weight-length relationship in Anableps anableps (Linnaeus, 1758) (Cyprinodontiformes: Anablepidae) from the Amazon Estuary
(2011) OLIVEIRA, Valéria de Albuquerque; FONTOURA, Nelson Ferreira; MONTAG, Luciano Fogaça de Assis
The present study analyzed the length-weight relationship and some aspects of the reproductive biology of Anableps anableps from the mouth of the Maracanã River, in the Brazilian state of Pará. The specimens were collected using two 30 m-long gillnets with 15 and 20 mm mesh size, as well as a 1 m-diameter hand net with a 10 mm mesh. A total of 865 specimens were collected, from which an adult sex ratio of 2.12 females per male was recorded (χ² = 13.07; p<0.05). Females presented positively allometric growth, whereas males were negatively allometric. In the additional analyses, the gonads of 371 female specimens were observed microscopically. Gonadal development was classified in three stages: immature (5.0%), maturing (12.0%), and mature (83.0%). Embryonic development was classified in five phases, according to the size of the embryo and the vitelline sac. Mean fecundity was 12 eggs/embryos per female (range: 1-37 eggs/embryos). A significant relationship was recorded between the standard length of females and ovaries weight (R² = 0.257; p < 0.001), and the number of embryos carried (R² = 0.573; p < 0.001). Mean body length of females at initial sexual maturation (L50) was estimated at 11.7 cm. The species reproduced throughout the year.
Acesso aberto (Open Access)
Seasonal changes in the gonadossomatic index, allometric condition factor and sex ratio of an auchenipterid catfish from eastern Amazonia
(2011) FREITAS, Tiago Magalhães da Silva; ALMEIDA, Vitor Hudson da Consolação; MONTAG, Luciano Fogaça de Assis; ROCHA, Rossineide Martins da; FONTOURA, Nelson Ferreira
The aim of the present study was to evaluate the seasonal pattern of the gonadosomatic index (GSI), condition factor (K), and sex ratio in the catfish Auchenipterichthys longimanus (Siluriformes: Auchenipteridae) as an approach to identify its reproductive period. A total of 589 A. longimanus specimens (251 males and 338 females) were captured in the rivers of the Caxiuanã National Forest, in the Brazilian state of Pará, between July, 2008 and July, 2009. Among the male specimens, 171 were classified as adults and 80 as juveniles, while there were 249 adults and 89 juvenile females. Using a sinusoidal equation, analysis of the GSI revealed a reproductive asynchrony between the genders, with males attaining their highest GSI values in January, while females peaked in March. For males, the sinusoidal regression for GSI values was significant only when used the complete data set (P=0.001), wears no trend was identified for bimonthly means (P=0.136). For females, by contrast, significant values were obtained for both the complete data set (P=0.012) and bimonthly GSI means (P=0.026). For the condition factor, the sinusoidal equation returned significant seasonal variation in both raw data (P=0.02) and with mean values (P=0.00) for males, but only with raw data for females (P=0.04), which appears to reflect variation in the energy budget between genders. With regard to the sex ratio, more reproductive females were captured than males in January and March, 2009, which suggests a pattern of segregation related to the reproductive process. These parameters are fundamental to the assessment, protection, and management of natural fish stocks, as well as providing guidelines for the development of conservation strategies.