Tiago Magalhães da Silva Freitas

Seasonal changes in the gonadossomatic index, allometric condition factor and sex ratio of an auchenipterid catfish from eastern Amazonia

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 Caxiuana National Forest, in the Brazilian state of Para, 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.

Feeding ecology of Auchenipterichthys longimanus (Siluriformes: Auchenipteridae) in a riparian flooded forest of Eastern Amazonia, Brazil

Neste estudo foram investigados os habitos alimentares do bagre Auchenipterichthys longimanus coletados em rios da Floresta Nacional de Caxiuana (Amazonia Oriental, Brasil) ao longo de diferentes periodos hidrologicos (seco, enchendo, cheio e vazando). Foram coletados 589 especimes durante sete amostragens, entre julho de 2008 e julho de 2009, dos quais 74eram machos jovens, 177 machos adultos, 89 femeas jovens e 249 femeas adultas. A composicao da dieta, analisada pelo Indice de Importância Alimentar (IAi%) foi avaliada por um escalonamento multidimensional nao-metrico (nMDS) e pela analise de similaridade (ANOSIM), que incluiu 37 itens alimentares agrupados em nove categorias (insetos aquaticos, outros invertebrados aquaticos, fragmento de artropodes, peixe, fragmento de planta, sementes, insetos terrestres, outros invertebrados terrestrese vertebrados terrestres). Tambem foram obtidos a amplitude de nicho (Indice de Levins) e o Indice de Replecao (IR%) da dieta do bagre. Foram observadas diferencas na composicao da dieta entre os periodos hidrologicos, principalmente relacionada a estacao seca e cheia, mas nao houve variacao na composicao da dieta entre os sexos e maturidade. No periodo de cheia (especificamente no mes de marco/2009) o bagre mostrou uma alimentacao mais especialista enquanto que no periodo de seca (novembro/2008) os valores de amplitude de nicho classificaram-no com habitos mais generalistas quanto a alimentacao. A quantidade de alimentos ingeridos por A. longimanus com base no Indice de Replecao (IR%), nao diferiram significativamente entre o sexo e maturidade. No entanto, foram evidenciadas diferencas quando comparados os meses estudados. Estes resultados fornecem informacoes biologicas importantes sobre a ecologia trofica de peixes da familia Auchenipteridae. Tendo em vista a maior ocorrencia de itens aloctones na dieta deste bagre, esta pesquisa tambem reforca a importância das matas ciliares em ambientes criticos na manutencao e conservacao das populacoes selvagens de peixes na bacia amazonica.

Length-weight relationship and reproduction of the guppy Poecilia reticulata (Cyprinodontiformes: Poeciliidae) in urban drainage channels in the Brazilian city of Belém

This paper describes the length-weight relationship, size at first maturation (L), and breeding season of Poecilia reticulata found in drainage channels on the campus of the Federal University of Para (UFPA) in the Brazilian city of Belem. A total of 1.936 specimens (942 males and 994 females) were collected in monthly samples of the study area between June, 2006, and March, 2007. Females were significantly longer and heavier than males. The length-weight relationship for males was established by the equation Pt = 5 × 10-5 × Ct2.397 and for females by Pt = 3 × 10-6 × Ct3.419. The estimated value of L was 17.5 mm for males and 20.4 mm for females, suggesting that males initiate reproductive activity at a smaller size than females. The abundance of mature females did not vary significantly among months, and there was little variation in the sex ratio, which was close to parity overall. Despite the adverse conditions encountered in the UFPA drainage system, P. reticulata appeared to have adapted its biological processes adequately.

Length-weight relationship in ten fish species from the Nhamundá River, the Amazon Basin, Brazil

Studies on the length-weight relationship (LWR) of fishes are an important tool to describe several biological aspects of the species. Consequently, these studies are relevant due the necessity of comprehension about fish life cycle. Thus, this study aimed to establish the length-weight relationship of the ten most common fish in the Lower Nhamunda River, left tributary of the Amazon River. The capture of fish was conducted in January 2008 using gill nets. A total of 807 individuals, ten species and three Orders (Characiformes, Siluriformes and Clupeiformes) were analyzed. The parameter b varied from 2.680 to 3.698. The LWR were shown for the first time for two species: Anostomoides laticeps and Ageneiosus polystictus. Finally, this research emphasizes the importance of LWR studies in the Amazon and the use of primary data for fisheries management plans.

Polychromatism of populations of Corallus hortulanus (Squamata: Boidae) from the southern Amazon Basin, Brazil

The Amazon tree boa Corallus hortulanus is known for featuring a wide variation in color pattern and design markings. Although there are studies on its polychromatism, none of them addresses the geographic variation in the color pattern of this species. The aim of this study was to describe the chromatic variation found in the populations of C. hortulanus from the southern Amazon Basin and its relationship with geographic distribution of the species. Analysis of both design markings and color patterns on 112 C. hortulanus specimens from the southern Amazon Basin interfluves resulted in the identification of six distinct morphotypes. Grayish-brown coloration and elongated diamond-shaped patterns were the most frequent patterns. Two morphotypes showed a tendency of correlation with the geographical distribution of those species found in Madeira and Jurua Rivers. The small sample size does not allow for a robust conclusion on the possible cause of geographic variation. The distribution of morphological patterns of C. hortullanus in the Amazon Basin suggest that there is gene flow between populations, regardless of geographical distance and natural barriers. The variation in color pattern and markings may represent a phenotypic response to the characteristics of different habitats occupied by the species.

Predicting size at first sexual maturity from length/weight relationship: a case study with an Amazonian catfish

O estudo da relacao entre peso e comprimento e usado para investigar muitos aspectos do ciclo de vida dos peixes, mas nao considera que o padrao de crescimento pode mudar durante o tempo vida, principalmente devido a maturacao sexual. Desta forma, este estudo objetivou identificar o tamanho de primeira maturacao do bagre Auchenipterichthys longimanus (Siluriformes: Auchenipteridae) e testar se inicio do engajamento reprodutivo pode ser responsavel por mudancas no padrao de crescimento da especie, concernindo a relacao peso/comprimento. Estimativas de tamanho de primeira maturacao sexual (L50) foram realizadas por meio da identificacao visual dos estagios de maturacao e pelos valores do Indice Gonadossomatico (IGS). O L50 foi estimado em 12,5 cm para machos e 13,0 cm para femeas quando aplicados a identificacao visual dos estagios de maturacao. A estimativa do L50 aumentou para 13,05 cm para machos e 13,7 cm para femeas quando aplicados os valores de IGS. A relacao peso/comprimento foi ajustada utilizando uma funcao potencia e pelo modelo de crescimento polifasico, com coeficientes de proporcionalidade e alometrico diferentes para duas fases. Os resultados indicam diferencas no padrao de crescimento de machos e femeas, alem de um crescimento polifasico para ambos os sexos. A mudanca no padrao de crescimento foi estimada em 11,42 cm para machos e 12,53 cm para femeas, sugerindo que essas mudancas podem estar associadas ao inicio da vida reprodutiva desse bagre.