Can La Redonda lagoon (Cuba) be a suitable habitat for largemouth bass (Micopterus salmoides, Lacepède) recovery?

For decades, La Redonda lagoon was an excellent location for fishing the largemouth bass (Micopterus salmoides, Lacepède) in Cuba. There are indications that the species disappeared from the lagoon in 2009. Three water surveys were carried out in 2013 and 2014. Physicochemical parameters, including nutrients, were measured in all surveys. Chlorophyll a and water transparency were only measured in November 2013. Results showed that this lagoon is a fresh to brackish water system, with common salinization episodes. There were some hypoxic conditions, but mean dissolved oxygen value was above 5.0 ± 2.8 mg L−1 for the entire survey period. The trophic state was evaluated as oligotrophic and Nitrogen and Phosphorus were limiting in most of the survey sites. The Habitat Suitability Index model (HSI) for largemouth bass had a mean value of 0.63 ± 0.02 (moderate degree of suitability). All results showed that bass recovery could be possible in La Redonda lagoon, but management criteria are necessary. The largemouth bass recovery could help to increase visitations of American anglers to this place and a portion of the revenue could be used to conduct environmental monitoring and studies of the largemouth bass ecology in Cuba.

Genetic diversity and population structure of Hemibagrus guttatus (Bagridae, Siluriformes) in the larger subtropical Pearl River based on COI and Cyt b genes analysis

Understanding the genetic diversity and population structure of fish species is crucial for the sustainable use and protection of fish germplasm resources. Hemibagrus guttatus (Bagridae, Siluriformes) is widely distributed in the large subtropical Pearl River (China) and is commercially important. It's population have been declining. The genetic diversity of wild H. guttatus is not clear, despite its important ecological significance. In this paper, genes mitochondrial cytochrome c oxidase subunit I (COI) and cytochrome b (Cyt b) were used to analyze the genetic structure of H. guttatus population collected from six geographical populations in the main streams of the Pearl River. The results showed that the nucleotide diversity (π) and haplotype diversity (Hd) of wild H. guttatus was low (π < 0.005; Hd < 0.5). In addition, H. guttatus haplotypes did not cluster into clades according to geographical distribution, as revealed by neighbor-joining tree analysis. Analysis of molecular variance analysis (AMOVA) and F-statistics (Fst) values showed high homogeneity among wild H. guttatus populations. Our results suggest that there is degradation in germplasm resources of H. guttatus that could destabilize the sustainable use of this species and there was an urgent need for conservation of this species in South China.

Bottom-up and top-down effects on phytoplankton functional groups in Hulun Lake, China

The debates about the extent to which phytoplankton in freshwater ecosystems are regulated by top-down or bottom-up forces have been ongoing for decades. This study examines the effects of bottom-up and top-down factors on the phytoplankton functional groups in a eutrophic lake. Phytoplankton and zooplankton were sampled and physical-chemical variables measured from May 2019 to October 2019 in Lake Hulun, China. Approximately 43 phytoplankton species were observed and grouped into 23 functional groups. For the zooplankton, about 27 species were observed and classified into 8 functional groups. The study revealed that the bottom-up effects of physical-chemical variables on some phytoplankton functional groups was stronger than the top-down effects of zooplankton. Water temperature (WT), total phosphorus (TP), total nitrogen (TN), conductivity (Cond), water transparency (SD), and dissolved oxygen (DO) significant influence the biomass of the phytoplankton functional groups. The biomass of phytoplankton functional groups was influenced positively by nutrient availability likely because nutrients influence the growth and reproduction of phytoplankton in freshwater. WT and DO had a positive influence on biomass of phytoplankton functional groups. Conversely, phytoplankton biomass revealed a decreasing trend when SD and Cond significantly increased. This study showed that zooplankton functional groups were positively correlated with phytoplankton biomass implying that the top-down control of phytoplankton by the zooplankton in the lake is not strong enough to produce a negative effect. It is evident that the zooplankton functional groups in Lake Hulun are controlled more by bottom-up force than top-down.

Fungal richness does not buffer the effects of streams salinization on litter decomposition

Freshwater salinization is a world-wide phenomenon threatening stream communities and ecosystem functioning. In these systems, litter decomposition is a main ecosystem-level process where fungi (aquatic hyphomycetes) play a central role linking basal resource and higher levels of food-web. The current study evaluated the impact of aquatic hyphomycete richness on leaf litter decomposition when subjected to salinization. In a microcosm study, we analysed leaf mass loss, fungal biomass, respiration and sporulation rate by fungal assemblages at three levels of species richness (1, 4, 8 species) and three levels of salinity (0, 8, 16 g NaCl L‑1). Mass loss and sporulation rate were depressed at 8 and 16 g NaCl L‑1, while fungal biomass and respiration were only negatively affected at 16 g L‑1. A richness effect was only observed on sporulation rates, with the maximum values found in assemblages of 4 species. In all cases, the negative effects of high levels of salinization on the four tested variables superimposed the potential buffer capacity of fungal richness. The study suggests functional redundancy among the fungal species even at elevated salt stress conditions which may guarantee stream functioning at extreme levels of salinity. Nonetheless, it also points to the possible importance of salt induced changes on fungal diversity and identity in salinized streams able to induce bottom-up effects in the food webs.

Functional feeding groups of Protist Ciliates (Protist: Ciliophora) on a neotropical flood plain

Functional diversity approaches have been an efficient tool in gaining a better understanding of how environmental conditions selected species in a given environment and how they share resources, linking ecological processes to biodiversity patterns. Although most of the protist ciliates are not highly specialized, functional feeding groups with species which ingest similar food can be identified. Thus, this study aimed to compare the abundance of different Functional Feeding Groups (FFG) of ciliates in environments with different hydrodynamic conditions (lotic and lentic) in different hydrological periods (high and low water) in a neotropical flood plain. The samples for analysis of the community of ciliates were taken in March and September of 2010 and 2011, at the subsurface of 12 different hydrodynamic environments. The results of an RDA showed a spatial and temporal segregation of the sampling units, based on the abundance and occurrence of the FFG. In addition, a clear influence of food resources on the structuring of functional ciliate guilds was evidenced. Thus, there were both temporal (hydrological periods) and spatial (different hydrodynamic environments) differences in the distribution of the FFG, with a clear separation of the FFGs between the years studied. In summary, the results of the categorization of species of ciliates in FFG responded satisfactorily suggesting fluctuations in different food resources, which reinforces the idea that the grouping of species by functional characteristics can be a good indicator of the responses of organisms to environmental fluctuations.

Historical analysis of a karst aquifer: recharge, water extraction, and consumption dynamics on a tourist island (Cozumel, Mexico)

On Cozumel Island, access to freshwater depends on the extraction of the resource from the aquifer located north of the island (catchment area). Water resource management on the island must be based on updated knowledge of the indicator dynamics related to the recharge of the aquifer, groundwater extraction and the distribution of the resource. In this study, trends, variations and time series of 30 years of monthly data for precipitation, temperature, evapotranspiration, and estimated aquifer recharge were calculated for the catchment area. Additionally, groundwater extraction, water consumption for the main uses over a 13-year period (monthly data), and the 5-year status of wells were considered. The results show decreasing trends in precipitation and estimated recharge volumes in the catchment area, in addition to increasing trends in mean air temperature, evapotranspiration, water extraction volumes and consumption by the commercial sector for the considered time periods. Additionally, an increase in dejected (77%) and reposed (38%) wells within the catchment area was observed. Evidence from this study suggests a dynamic behaviour of the analysed indicators over time that increases pressure on karstic, Caribbean aquifers for which monthly monitoring and data analysis are encouraged as the basis for adequate management.

Effects of acute triclosan exposure on gill and liver tissues of zebrafish (Danio rerio)

Triclosan (TCS) is a broad-spectrum antimicrobial agent found in personal care, household, veterinary, medical, and industrial products. TCS has been detected in soil, sediment, and surface water. In the current work, the effects of acute exposure to TCS on gill and liver tissues of zebrafish were evaluated. Adult zebrafish were treated with sublethal concentrations of TCS (34, 85, and 170 μg/L) for 120 h. Gill and liver samples were removed and embedded in paraffin for histopathological investigations. TCS induced aneurysm, capillary dilation, lamellar disorganization, hyperplasia, epithelial lifting, and desquamation in the gills. Liver specimens showed sinusoidal dilation, congestion, vacuolization, hepatocellular degeneration, and necrosis. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay was performed to observe the apoptotic effect of TCS. Accordingly, no apoptotic cells were detected in the specimens of 34 μg/L of TCS exposed gills, while the slides of 85 and 170 μg/L of TCS treated gills showed a high number of TUNEL-positive cells. In the liver, no TUNEL-positive cells were identified in 34 μg/L of TCS treated samples of zebrafish. 85 and 170 μg/L of TCS exposed livers showed few hepatic parenchymal cells undergoing apoptosis.

Acute Exposure to the Neonicotinoid Insecticide Imidacloprid of Zebrafish (Danio rerio) Gonads: A Histopathological Approach

Neonicotinoids are the new class of insecticides that are high target specificity to insects. Imidacloprid is a neonicotinoid that is the most widely used insecticide in the world. As a result of its widespread use in agriculture, imidacloprid interferes with the aquatic system and threatens the aquatic environment. In this study, an investigation of the histopathological effects of imidacloprid on zebrafish gonads was aimed. Zebrafish were exposed to 9.5 mg/L, 19 mg/L, and 38 mg/L of imidacloprid for 5 days, considering the 96 h LC50 value. After dissecting the gonadal tissues, routine histological techniques were applied, and the tissues were stained with Periodic Acid-Schiff (PAS), Toluidine Blue (TB), and Haematoxylin and Eosin (H&E). Sections were examined under a light microscope. While normal gonad histology was observed in the control group, histopathological alternations such as degeneration and union in the seminiferous tubules, hypertrophy in spermatogenic and Leydig cells, and interstitial fibrosis were detected in testicular tissue of the experimental groups. In the ovarian tissues of the experimental groups, structural deterioration in oocytes, autolysis, increase in the number of atretic oocytes, vacuolization in cortical alveoli, thickening and curling in the zona radiata, and opening in the perifollicular layers were detected.

Spatial and temporal variation in species composition of ciliates communities (Alveolata, Ciliophora) from tropical urban and rural streams

The aim of this study was to investigate the spatial and temporal patterns in species composition of ciliates, in rural streams, affected by agricultural activities, and urban streams, impacted by domestic wastewater. Samplings were taken in two different periods of the year, in the headwater, middle and mouth stretch of ten streams. We recorded 143 species of ciliates, distributed in 14 groups, standing out Hymenostomatia, Peritrichia and Hypotrichia. Our results showed significant spatial (between rural and urban streams) and, especially, temporal differences (between winter and summer periods) in the ciliates taxonomic composition. Such differences seem to be not related to the organic load that was quite similar among streams and periods sampled. Rather, the changes in ciliates composition are probably driving mainly by other enviromental variables such as resources, determined by the spatial diferences in light availability, and flow water velocity and discharge, which present high temporal dissimilarity.

Aquarium trade and fish farms as a source of non-native freshwater fish introductions in French Guiana

Rivers of French Guiana are still little invaded by non-native fish, but several fish introductions were recently recorded through the development of aquarium fish trade and fish farms. Here we report records of 11 non-native fish species. Among them, four (Cichla monoculus, Heros efasciatus, Mesonauta guyanae and Poecilia reticulata) are established and one of them (Heros efasciatus) is rapidly increasing its spatial range. Two species (Hyphessobrycon eques and Pterophyllum scalare) were not retrieved in recent records and are probably extinct from French Guiana. The establishment status of the five other species (Arapaima gigas, Colossoma macropomum, Cyprinus carpio, Oreochromis mossambicus and Osteoglossum bicirrhosum) is uncertain and only a few specimens were observed in the wild. Nevertheless, these species, intensively reared in nearby countries, belong to highly invasive species able to cause detrimental impacts on recipient ecosystems. Those first occurrences of invasive fish species in French Guiana should therefore act as an early warning for both researchers and environmental managers.