'Cand. Actinochlamydia clariae' gen. nov., sp. nov., a Unique Intracellular Bacterium Causing Epitheliocystis in Catfish (Clarias gariepinus) in Uganda

Background and Objectives: Epitheliocystis, caused by bacteria infecting gill epithelial cells in fish, is common among a large range of fish species in both fresh-and seawater. The aquaculture industry considers epitheliocystis an important problem. It affects the welfare of the fish and the resulting gill disease may lead to mortalities. In a culture facility in Kampala, Uganda, juveniles of the African sharptooth catfish (Clarias gariepinus) was observed swimming in the surface, sometimes belly up, showing signs of respiratory problems. Histological examination of gill tissues from this fish revealed large amounts of epitheliocysts, and also presence of a few Ichthyobodo sp. and Trichodina sp. Methods and Results: Sequencing of the epitheliocystis bacterium 16S rRNA gene shows 86.3% similarity with Candidatus Piscichlamydia salmonis causing epitheliocystis in Atlantic salmon (Salmo salar). Transmission electron microscopy showed that the morphology of the developmental stages of the bacterium is similar to that of members of the family Chlamydiaceae. The similarity of the bacterium rRNA gene sequences compared with other chlamydia-like bacteria ranged between 80.5% and 86.3%. Inclusions containing this new bacterium have tubules/channels (termed actinae) that are radiating from the inclusion membrane and opening on the cell surface or in neighbouring cells. Conclusions: Radiation of tubules/channels (actinae) from the inclusion membrane has never been described in any of the other members of Chlamydiales. It seems to be a completely new character and an apomorphy. We propose the name Candidatus Actinochlamydia clariae gen. nov., sp. nov. (Actinochlamydiaceae fam. nov., order Chlamydiales, phylum Chlamydiae) for this new agent causing epitheliocystis in African sharptooth catfish

The effects of cyanobacteria on the growth, survival and behaviour of a tropical fish (Nile tilapia) and zooplankton (Daphnia lumholtzi)

Recent studies on the ecological effects of cyanobacteria in lakes have focused on the harmful effects of blooms to other aquatic organisms including fish and zooplankton. Much of this work has been conducted on temperate and subtropical species whilst few studies have involved tropical species, despite the almost chronic occurrence of cyanobacteria blooms in eutrophic tropical lakes. The main purpose of this study was to fill some of this knowledge gap on the ecological effects of cyanobacteria on fish and zooplankton in tropical lakes and to discover in what ways tropical species may be better adapted to deal with cyanobacteria than temperate species. The study tested fish (Nile tilapia, Oreochromis niloticus L.) and zooplankton growth, survival, and behaviour in relation to different variants (toxic and non toxic) and species of cyanobacteria at varying quantities as well as environmental conditions. Field studies on the diet and presence of cyanobacteria toxins (microcystins) in the guts and tissues (muscle and liver) of Nile tilapia were carried out in two eutrophic tropical aquatic ecosystems (Lake Mburo and Murchison Bay, Lake Victoria) in Uganda, East Africa. The zooplankton behaviour of diel vertical migration (DVM) was investigated in the Murchison Bay in relation to environmental conditions. Laboratory studies investigated the effect of the cyanotoxins, microcystins, on Nile tilapia and zooplankton (Daphnia lumholtzi) growth, survival, and behaviour, using the toxic cyanobacterium Microcystis aeruginosa PCC 7806. Cyanobacteria are the most abundant phytoplankton group in the two study areas contributing to over 60% of the total phytoplankton biovolume. The most dominant cyanobacteria species is Microcystis sp. which makes up approximately 70% of the total cyanobacteria biovolume. Low water transparencies were well associated with high levels of chlorophyll a in the lakes, suggesting that the abundance of cyanobacteria in these lakes may have a significant effect on the light environment. Water transparency is observed to have a close association with the DVM behaviour of at least one zooplankton group in the Murchison Bay. Phytoplankton especially of the cyanobacteria is an important diet item (> 30%) to the Nile tilapia in both lakes. Microcystins (RR, LR &YR) were detected in water samples from both study lakes and in the Murchison bay the concentration of microcystins in water was well associated with the microcystins concentration in the gut of Nile tilapia (p<0.05). Although detected, we found no evidence of microcystin accumulation in the liver or muscle tissue. The ingestion rates and growth rates of juvenile Nile tilapia were not significantly affected by the presence of microcystins in their diets. Likewise growth and survival rates of the tropical cladoceran Daphnia lumholtzi in laboratory experiments were not significantly affected by the presence of microcystins in their diets. The cyanobacteria M. aeruginosa PCC7806 was a poor source of nutrients for juvenile fish and zooplankton, since it did not seem to stimulate growth both in the wild type and mutant type form. Though microcystins were present throughout the study period, our findings do not show that they have a strong effect on the diets of Nile tilapia. Nile tilapia in these lakes probably ingest cyanotoxins mostly through the cell-bound fraction, since cyanobacteria (especially Microcystis sp.) are an important constituent of their diet. Adult fish may have the ability to efficiently get rid of ingested cyanotoxins, but this may not be so for juvenile tilapia and zooplankton. Small amounts of cyanobacteria may actually stimulate growth in juvenile tilapia and even zooplankton, yet when provided in high proportions or as the sole source of nutrients they hinder growth, survival, and reproduction. Juvenile fish and most especially zooplankton, are unlikely to graze on cyanobacteria either due to their frequent formation of large colonies or because juvenile fish and zooplankton may lower their ingestion rates in the presence of cyanotoxins. Findings in this study do not provide any evidence for tolerance of tropical juvenile fish and zooplankton towards cyanobacteria toxins, yet adult fish show both the ability to utilise cyanobacteria and cope with levels of microcystins registered in the lakes

Hyperspectral total upward sea surface leaving radiance observed at 45° nadir angle observed during cruise aboard RV IBIS on Lake Victoria, Uganda, from 13 to 15 October 2021

Hyperspectral radiometric quantities were observed at a 5-minute sampling interval in the Ugandan portion of Lake Victoria during a scientific field campaign aboard research vessel (RV) IBIS from 13 to 15 October 2021. The three day fieldwork was cooridnated starting from the Napoleon Bay, Jinja, Uganda. A radiometer setup one TriOS RAMSES-ARC hyperspectral radiance meters to measure total upward sea surface leaving radiance (Lsfc) at 45° nadi was installed using a custom-made frame at the bow of RV IBIS. Data logging of raw and calibrated radiometric quantities was automated using TriOS MSDA XE version 8.9.2 software. Further processing was done using Mathworks Matlab 2016a and R software. Processed data was interpolated to 1 nm spectral resolution using PCHIP function in Matlab between 320 and 950 nm. Only the data with valid GPS coordinates and with spectra contributing less than 3% is included in this file, the rest of the data is available on request

Hyperspectral downward irradiance observed during cruise aboard RV IBIS on Lake Victoria, Uganda, from 13 to 15 October 2021

Hyperspectral radiometric quantities were observed at a 5-minute sampling interval in the Ugandan portion of Lake Victoria during a scientific field campaign aboard research vessel (RV) IBIS from 13 to 15 October 2021. The three day fieldwork was cooridnated starting from the Napoleon Bay, Jinja, Uganda. A radiometer setup with one TriOS RAMSES-ACC hyperspectral cosine irradiance meter to measure incoming solar irradiance was installed using a custom-made frame at the bow of RV IBIS. Data logging of raw and calibrated radiometric quantities was automated using TriOS MSDA XE version 8.9.2 software. Further processing was done using Mathworks Matlab 2016a and R software. Processed data was interpolated to 1 nm spectral resolution using PCHIP function in Matlab between 320 and 950 nm. Only the data with valid GPS coordinates and with spectra contributing less than 3% is included in this file, the rest of the data is available on request

Hyperspectral above-water radiometric quantities observed during cruise aboard RV IBIS on Lake Victoria, Uganda, from 13 to 15 October 2021

Hyperspectral radiometric quantities were observed at a 5-minute sampling interval in the Ugandan portion of Lake Victoria during a scientific field campaign aboard research vessel (RV) IBIS from 13 to 15 October 2021. The three-day fieldwork was coordinated starting from the Napoleon Bay, Jinja, Uganda. A radiometer setup with one TriOS RAMSES-ACC hyperspectral cosine irradiance meter to measure incoming solar irradiance and two TriOS RAMSES-ARC hyperspectral radiance meters to measure total upward sea surface leaving radiance (Lsfc) at 45° nadir and sky-leaving radiance (Lsky) at 45° zenith angle, was installed using a custom-made frame at the bow of RV IBIS. Data logging of raw and calibrated radiometric quantities was automated using TriOS MSDA XE version 8.9.2 software. Further processing was done using Mathworks Matlab 2016a and R software. Processed data was interpolated to 1 nm spectral resolution using PCHIP function in Matlab between 320 and 950 nm. Only the data with valid GPS coordinates and with spectra contributing less than 3% is included in this file, the rest of the data is available on request

Hyperspectral downward sky leaving radiance observed at 45° zenith angle during cruise aboard RV IBIS on Lake Victoria, Uganda, from 13 to 15 October 2021

Hyperspectral radiometric quantities were observed at a 5-minute sampling interval in the Ugandan portion of Lake Victoria during a scientific field campaign aboard research vessel (RV) IBIS from 13 to 15 October 2021. The three day fieldwork was cooridnated starting from the Napoleon Bay, Jinja, Uganda. A radiometer setup one TriOS RAMSES-ARC hyperspectral radiance meters to measure total upward sky-leaving radiance (Lsky) at 45° zenith angle was installed using a custom-made frame at the bow of RV IBIS. Data logging of raw and calibrated radiometric quantities was automated using TriOS MSDA XE version 8.9.2 software. Further processing was done using Mathworks Matlab 2016a and R software. Processed data was interpolated to 1 nm spectral resolution using PCHIP function in Matlab between 320 and 950 nm. Only the data with valid GPS coordinates and with spectra contributing less than 3% is included in this file, the rest of the data is available on request

High nutrient loading and climatic parameters influence the dominance and dissimilarity of toxigenic cyanobacteria in northern bays of Lake Victoria

International audienc

A review of the socioecological causes and consequences of cyanobacterial blooms in Lake Victoria

International audienceAfrica is experiencing high annual population growth in its major river basins. This growth has resulted in significant land use change and pollution pressures on the freshwater ecosystems. Among them, the Lake Victoria basin, with more than 42 million people, is a unique and vital resource that provides food and drinking water in East Africa. However, Lake Victoria (LV) has experienced a progressive eutrophication and substantial changes in the fish community leading to recurrent proliferation of water hyacinth and cyanobacteria. Based on an extensive literature review, we show that cyanobacterial biomasses and microcystin concentrations are higher in the bays and gulfs (B&Gs) than in the open lake (OL), with Microcystis and Dolichospermum as the dominant genera. These differences between the B&Gs and the OL are due to differences in their hydrological conditions and in the origins, type and quantities of nutrients. Using data from the literature, we describe the multiple ways in which the human population growth in the LV watershed is connected to the increasing occurrence of cyanobacterial blooms in the OL and B&Gs. We also described the consequences of cyanobacterial blooms on food resources and fishing and on direct water use and water supply of local populations, with their potential consequences on the human health. Finally, we discuss the actions that have been taken for the protection of LV. Although many projects have been implemented in the past years in order to improve the management of waste waters or to reduce deforestation and erosion, the huge challenge of the reduction of cyanobacterial blooms in LV by the control of eutrophication seems far from being achieved

Characterization of Potential Threats from Cyanobacterial Toxins in Lake Victoria Embayments and During Water Treatment

Africa’s water needs are often supported by eutrophic waterbodies dominated by cyanobacteria posing health threats to riparian populations from cyanotoxins, and Lake Victoria is no exception. In two embayments of the lake (Murchison Bay and Napoleon Gulf), cyanobacterial surveys were conducted to characterize the dynamics of cyanotoxins in lake water and water treatment plants. Forty-six cyanobacterial taxa were recorded and out of these 14 were considered potentially toxigenic (i.e., from the genera Dolichospermum, Microcystis, Oscillatoria, Pseudanabaena and Raphidiopsis). A higher concentration (ranging from 5-10 µg MC-LR equiv. L-1) of microcystins (MCs) was detected in Murchison Bay compared to Napoleon Gulf, with a declining gradient from the inshore (max. 15 µg MC-LR equiv. L-1) to the open lake. In Murchison Bay, an increase either in Microcystis sp. biovolume and MC was observed over the last two decades. Despite high cell densities of toxigenic Microcystis and high MC concentrations, the water treatment plant in Murchison Bay efficiently removed the cyanobacterial biomass, intracellular and dissolved MC to below the lifetime guideline value for exposure via drinking water (< 1.0 µg MC-LR equiv. L-1). Thus, the potential health threats stem from the consumption of untreated water and recreational activities, along the shores of the lake embayments. MC concentrations were predicted from Microcystis cell numbers regulated by environmental factors such as solar radiation, wind speed in the N-S direction and turbidity. Thus, an early warning through microscopical counting of Microcystis cell numbers is proposed to better manage health risks from toxigenic cyanobacteria in Lake Victoria