RESUMONo presente trabalho foram analisados os parâmetros de crescimento, a relação peso-comprimento e a influência da variação sazonal do rio Miranda, alto rio Paraguai, sobre o período reprodutivo de Prochilodus lineatus. As amostragens foram realizadas mensalmente entre abril/2000 e outubro/2003. A equação que descreve a relação peso-comprimento total para fêmeas foi Pt=0,01213*Ct 3,039 e para os machos Pt=0,01322*Ct 3,012 . O comprimento total assintótico estimado foi de 55,68cm e taxa de crescimento K = 0,46/ano e Rn = 0,183 foram estimados pela frequência de classes de comprimento. O tamanho de primeira maturação (L50) foi estimado em 28,2cm. O índice gonadossomático (IGS) variou significativamente entre os meses (H = 136,61; p < 0,01), com valores mais elevados entre setembro e dezembro, contudo foram encontradas fêmeas maduras de agosto a fevereiro. O IGS esteve positivamente correlacionado com a duração do dia (rs = 0,55; p < 0,05) e com a precipitação (rs = 0,65; p < 0,05), contudo, não esteve correlacionado com o nível do rio (rs = 0,48; p = 0,1), ainda que no período de enchente seja perceptível a co-variação entre GSI e o nível do rio. O aumento no comprimento do dia e o início das primeiras chuvas parecem atuar como sinais preditores para que as fêmeas possam iniciar a atividade reprodutiva, a fim de garantir aos ovos e larvas as condições ambientais ideais encontradas nos meses subsequentes de cheia, fato este verificado pela alta proporção de fêmeas maduras de setembro a dezembro. A expectativa de vida de 6,5 anos foi compatível com as 6 coortes estimadas pela curva de crescimento. Palavras-chave: tamanho de primeira maturação; crescimento; Pantanal. ABSTRACT POPULATION STRUCTURE, BREEDING SEASON AND GROWING OF Prochilodus lineatus INHEADWATER OF MIRANDA RIVER, UPPER PARAGUAI RIVER. In the present paper we analyzed growth parameters, length-weight relationship and the influence of seasonal variation of Miranda river, upper Paraguay River, on breading season of Prochilodus lineatus. The samples were accomplished monthly from April/2000 to October/2003. The length-weight relationship described for females was PT=0.01213*CP 3.039 and for males was PT=0.01322*Ct 3.012 . The estimated asymptotic total length was 55.68cm and the growth rate K = 0.46 and Rn = 0.183 were estimated by frequency of length classes. The estimated size at first maturity (L50) was 28.2cm. The gonadossomatic index (GSI) varied significantly among months (H = 136.61; p < 0.01), with significant higher values from September to December, however ripe females were caught from August to February. GSI was positively correlated with the day length (rs = 0.55; p < 0.05) and with rainfall (rs = 0.65; p < 0.05), however, it was not correlated with the river level (rs = 0.48; p = 0.1). The increasing in the duration of the day and the begin of the first rains seem to act as cues for females start the breeding activity, in order VICENTIN, W. et al. Oecol. Aust., 16(4): 891-904, 2012 892 to provide to eggs and larvae the optimum environmen...
Growth is a fundamental biological process, driven by multiple endogenous (intra-individual) and exogenous (environmental) factors that maintain individual fitness and population stability. The current study aims to assess whether individual, spatial (headwaters and floodplains) and inter-sex variation occurs in the growth of Piaractus mesopotamicus in the Cuiabá River basin. Samples were collected monthly from July 2006 to July 2007, at two areas in the Cuiabá River basin (headwaters and floodplain). Three growth models (individuals; individuals and sex factors; individuals and areas factors) were developed and compared the fish growth parameters using Akaike information criterion (AIC). The best fit to the length-at-age data was obtained by a model that considered individual variation and sex. The theoretical maximum average length (L ∞ ) was 64.99 cm for females, and 63.23 cm for males. Females showed a growth rate (k) of 0.230 yr -1 and males of 0.196 yr -1 . Thus, could be concluded that individual variability and sex were the main sources of variation in P. mesopotamicus somatic growth parameters.Keywords: Age, Growth models, Inter-sex variation, Otoliths, Von Bertalanffy O crescimento é um processo biológico fundamental, impulsionado por múltiplos fatores endógenos (intra-individual) e exógenos (ambientais) que mantém o fitness individual e a estabilidade populacional. Este trabalho tem como objetivo avaliar se ocorre variação individual, espacial (região de cabeceira e planície de inundação) e entre sexo no crescimento de Piaractus mesopotamicus na bacia do rio Cuiabá. Amostragens foram realizadas mensalmente entre julho de 2006 a julho de 2007, em duas áreas da bacia do rio Cuiabá (região de cabeceira e planície de inundação). Três modelos de crescimento (indivíduos, indivíduos e sexo como fator, indivíduos e área como fator) foram elaborados e comparados os parâmetros de crescimentos dos peixes com base no critério de Informação de Akaike (AIC). O melhor ajuste aos dados de comprimento na idade data foi obtido pelo modelo que considerou a variação individual e o sexo. O comprimento médio máximo teórico (L ∞ ) das fêmeas foi 64,99 cm e para os machos 63,23 cm. O coeficiente de crescimento (k) médio foi de 0,230 yr -1 e 0,196 yr -1 , respectivamente para fêmeas e machos. Portanto, pode-se concluir que variabilidade individual e sexo foram as principais origem de variação dos parâmetros de crescimento somático de P. mesopotamicus. Palavras-chave:Dimorfismo sexual, Idade, Modelos de crescimento, Otólitos,
Aim This study investigated changes in the dietary composition and trophic niche breadth of Eigenmannia desantanai in the context of hydrological periods, rivers, and ontogeny. Methods Collections were performed monthly on the Paraguay and Amonguijá Rivers between February 2009 and January 2011. Results A total of 338 specimens of E. desantanai were collected, 224 of which came from the Amonguijá River and 114 from the Paraguay River. In all, 21 food items were identified. Fully remains of digested animals (RDA), Chironomidae, Cladocera, and Ostracoda showed greater importance in the diet of E. desantanai. Dietary composition was influenced by hydrological periods, followed by differences between sampled rivers, and ontogeny. In contrast, only hydrological periods explained variation in the E. desantanai trophic niche breadth. Conclusions The diet of E. desantanai is mainly composed of Chironomidae, Cladocera, and Ostracoda; however, individuals consumed other food items owing to changes in hydrological periods, followed by characteristics of the Amonguijá and Paraguay Rivers and ontogenetic variation. In this respect, the results of this study are germane to the food ecology of E. desantanai, providing guidelines for the management and conservation of the species.
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