The Dendrocephalus brasiliensis, a native species from South America, is a freshwater crustacean well explored in conservational and productive activities. Its main characteristics are its rusticity and resistance cysts production, in which the hatching requires a period of dehydration. Independent of the species utilization nature, it is essential to manipulate its cysts, such as the counting using microscopes. Manually counting is a difficult task, prone to errors, and that also very time-consuming. In this paper, we propose an automatized approach for the detection and counting of Dendrocephalus brasiliensis cysts from images captured by a digital microscope. For this purpose, we built the DBrasiliensis dataset, a repository with 246 images containing 5141 cysts of Dendrocephalus brasiliensis. Then, we trained two state-of-the-art object detection methods, YOLOv3 (You Only Look Once) and Faster R-CNN (Region-based Convolutional Neural Networks), on DBrasiliensis dataset in order to compare them under both cyst detection and counting tasks. Experiments showed evidence that YOLOv3 is superior to Faster R-CNN, achieving an accuracy rate of 83,74%, R2 of 0.88, RMSE (Root Mean Square Error) of 3.49, and MAE (Mean Absolute Error) of 2.24 on cyst detection and counting. Moreover, we showed that is possible to infer the number of cysts of a substrate, with known weight, by performing the automated counting of some of its samples. In conclusion, the proposed approach using YOLOv3 is adequate to detect and count Dendrocephalus brasiliensis cysts. The DBrasiliensis dataset can be accessed at: https://doi.org/10.6084/m9.figshare.13073240.

Most studies on microplastic (MP) pollution in freshwaters consider large rivers and lakes, with streams relatively poorly studied. We analysed the temporal variation in abundance of MP particles in an urban stream draining commercial and residential areas, sampling on seven occasions during the course of nine months. We filtered samples through a nylon net of 68µm mesh size, carried out digestion with a novel method, namely WPO (H2O2 + Fe) followed by KOH, and analysed MP particles quantitatively and qualitatively by light microscopy. All samples contained MPs, with concentrations varying between 1.1 and 11.3 particles.L− 1. The most abundant forms were transparent filaments (found in 67% of the samples) and black fragments (found in 47% of the samples). MP concentrations were significantly positively related to the absence of rainfall. Mean transport was calculated to be 5.75x1011 items.year− 1. These abundances are equal or superior to those recorded in large rivers draining industrial areas, suggesting that small streams can be an important source of MP pollution.

Branchoneta is an option as live food for aquaculture and it is necessary to develop more studies to get information that makes possible its culture on a large scale. Our aim was to establish a method that results in a higher percentage hatching of D. brasiliensis. We analyzed if the cyst density could cause any significant difference in hatching; for that test we use 2 different conditions: (I) 15 ml glass tube (T1, T2, and T3) with 25 (twenty-five) cysts/repetition; and (II)  Erlenmeyer of 150 ml (T4, T5, and T6) with 25 cysts/repetition totaling 75 cysts/treatment, with triplicates to all treatments. We also tested 3 different pH conditions: acid (pH 3), neutral (pH~7/distilled water) and alkaline (pH 8), all in natural light and temperature. We conclude that there is no difference between the treatments, for none of the conditions tested. But other results have to be considered as Hatching Speed index and the Average Hatching Time with best results for the treatments T3, T1, and T2, respectively. The density of 0.6 ml/cyst (glass tube) resulted in faster hatching, which shows the necessity of further studies to analyze the speed of hatching under different conditions of density. The relative frequency showed that the hatchings peak occurs in the second day. We conclude that pH and density, in this study, not influenced the beginning of the hatching process.

Aim Knowledge of the factors influencing the biomass of phytoplankton in rivers is important with reference to the characterization of water quality and predicting the effects of environmental change on such ecosystems. The present study quantified the concentrations of chlorophyll-a in the water column of the Miranda River Basin, located in western Brazil, contributing to form the Pantanal Wetland, and attempted to identify the primary environmental influences on the phytoplankton biomass. Methods Temperature, depth, current speed, turbidity, Secchi transparency and concentrations of nutrients, suspended solids and chlorophyll-a were measured at approximate monthly intervals during the course of a year, at five upland and three lowland sites. Relationships between chlorophyll-a and nutrient concentrations, travel times and light availability were examined. Results Nutrient levels were generally low, being oligo- to mesotrophic. High levels of suspended solids were recorded (up to approximately 250 mg.L-1), especially in the rainy season at the upland sites. The latter showed low chlorophyll-a concentrations, while lowland sites, with the exception of one, showed two peaks, one in winter (dry season) and the other in summer (wet season), of 4.9 and 2.4µg.L-1, respectively, coincident with reduced concentrations of suspended solids. Conclusions The low nutrient levels recorded may have been due to the main land use being cattle rearing. The high solids concentrations found may have been due to the degradation of native vegetation, especially riparian, that has occurred over the past decades. Travel times of approximately three to four days may have been a factor in retarding algal abundance in the upland sites, as opposed to approximately ten days in the lowland sites, where light limitation may have been a factor reducing algal growth.