Here we choose the sábalo Prochilodus lineatus, to answer the following questions: How the otolith length and weight are correlated to fish measurements (length and weight)? How reliable are the otoliths measurements to predict the length and age of P. lineatus? Finally, we propose predictive equations of the length and weight of the fish using length and weight of the otolith. The otoliths were sampled from individuals collected in the Upper Paraná River floodplain during 2012 and 2013 years. The relationships among the otolith measurements and both length and weight of the fish were performed using linear regressions. To test whether the length and weight of the otolith differ between the sampled sites, Variance Analysis was performed. Finally, we made analysis of Kruskal-Wallis to verify if the measurements obtained through the otoliths could be used to distinguish the age of the fish. We demonstrate that the length and weight of the otolith are good proxies to predict the length and weight of the fish. Although some ages were statistically different, this result does not support the idea that the age of the fish can be accurately inferred only using otolith measures.
Summary
This work contributes to the knowledge of the reproduction, growth parameters and mortality rates of Iheringichthys labrosus in a newly‐formed reservoir. A total of 554 males and 1227 females were collected over 12 consecutive months, 1998–1999, from sites in the Corumbá Reservoir, Brazil, using gillnets (meshes: 2.4–16 cm). Information on each individual, i.e. standard length (cm), weight (g), sex, and gonadal development phase was recorded. The pectoral spines were removed to estimate age. The number of juveniles and adults, males and females, reproductive sites and seasons were estimated. First maturation length was estimated using a likelihood function fitted by binomial distribution. Growth parameters were estimated using the von Bertalanffy equation. Total instantaneous mortality was obtained through a linearized catch curve method. Standard length varied from 6.0 to 20.5 cm. Growth showed negative allometry for both sexes. The reproduction period was August to December in all environments sampled and first maturation length was 11.5 cm. All individuals were adults with 17.0 cm standard length. Ages varied from zero to 7 years. Asymptotic length, growth coefficient and t0 for the entire population were 27.79 cm, 0.12 and −2.64, respectively. Instantaneous and annual mortality rates were 0.90 and 0.59, respectively.
Environmental characteristics of an invaded environment can predict the invasion success of a species, depending on its habits and life strategies. Cichla kelberi is a visual and voracious predator introduced in the upper Paraná River floodplain, an area that suffers with several upstream dams that caused many environmental changes over the years (e.g. increased water transparency). As this species is a pre-adapted species to environments that presents high water transparency, our main goal was to test the hypothesis that variables related to the underwater visibility would be important drivers of the successful invasion of C. kelberi in the upper Paraná River floodplain. We predict that turbidity (proxy of water transparency) is one of the major limnological determinants of occurrence and abundance of C. kelberi. Individuals of the invasive species and seven limnological variables were sampled quarterly between February 2000 and November 2018. This long-term data is part of the sixth site of the Brazilian Long Term Ecological Program (PELD). We fitted two regression models to all occurrence and abundance data (response variables) against the limnological variables (explanatory variables). For occurrence data, we fitted a Generalized Linear Mixed Model and for abundance data, we fitted a Linear Mixed Effects Model. The occurrence data of C. kelberi showed that turbidity and dissolved oxygen were the variables that most influenced the presence of this species, negatively and positively, respectively. The abundance data showed that dissolved oxygen and concentration of chlorophyll-a were the ones that most influenced the abundance of this species, negatively and positively, respectively. Our findings showed that besides turbidity, other limnological variables were also determinants for the occurrence and abundance of C. kelberi. Therefore, our results provided important
Spatial synchrony occurs when the abundance of populations in different locations rise and fall together. This pattern is caused mainly by dispersal and spatially correlated environmental stochasticity. The levels of spatial synchrony can vary between species, yet little is known about which species traits can explain this interspecific variation. In addition, traits may have different degrees of influence on spatial synchrony levels because of their differences in plasticity. We hypothesized that conservative traits—reproductive and morphological—will best explain interspecific variation in synchrony, while those that may vary according to the environment—feeding and habitat preference—will be weakly related to this interspecific variation. We evaluated the spatial synchrony of freshwater fish species in a highly fragmented river in the Neotropical region and related the levels of synchrony to seven predictors: diet, reproductive traits (migration, fecundation, parental care and spawning), position in the water column, niche breadth, body size, body shape and average temporal occurrence of each species. The fish species showed low levels of spatial synchrony but a high interspecific variation (correlation values ranging from −0.11 to 0.41). We found that this variation was mainly related to species' reproductive traits, that is, sedentary species with partial spawning and without parental care had higher mean spatial synchrony than species with the opposite characteristics. In contrast, more plastic traits (diet and habitat preferences) were poor predictors of mean spatial synchrony. We speculate that, despite the low spatial synchrony found, if extreme impacts continue to occur in the basin at the regional scale, it may negatively affect local fish populations in a synchronous manner, resulting in increased risk of simultaneous declines.
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