In celebration of World Lake Day (https://www.unep.org/events/un-day/world-lake-day-2025), a United Nations awareness day highlighting the importance of lakes and their sustainable management, we spotlight research from across the BMC series on freshwater ecosystems.

BMC Zoology-The Prussian carp (Carassius gibelio) in Saskatchewan, Canada: current distribution and life history traits of a novel invasive species

A recent study published in BMC Zoology uncovers the spread of invasive fish in Saskatchewan River and its tributaries. The Prussian carp (Carassius gibelio) is an invasive fish species that has spread extensively across Europe, first detected in Alberta in early 2000. By 2018 researchers observed a spike in dead Prussian carp along Stockwell lake, implying Prussian carp had been established for some time in Saskatchewan. Authors developed citizen science program for a survey of the Prussian carp. By Employing  citizen science reports coupled with field surveys and 500,000 social media views to fish submission; the study confirmed Prussian carp were well established in region of Saskatchewan including South Saskatchewan river, lake Diefenbaker and multiple connecting tributaries. Their size ranges from 20mm to 42 cm, with some likely older than 10 years.

Authors noted that the population have a mix of ploidy i.e. diploid, triploid and tetraploid. Most spawning likely occurs during mid-June. This timing of spawning overlapped with that of a variety of native sucker and shiner species, but sperm donors for potential gynogenesis remain unidentified.

The Qu’Appelle Dam acts as a barrier and restricts dispersal in South Saskatchewan River at Lake Diefenbaker. The authors emphasized that it is essential to seriously evaluate the implementation of physical barriers or other active deterrent measures to prevent Prussian carp from accessing the deep-water intake. Additionally, it is recommended that management should prioritize minimizing their local ecological impacts and preventing further dissemination.

BMC Veterinary Research - Prevalence of Ligula intestinalis, histopathological investigation, and associated risk factors in Labeobarbus fish species at Lake Tana, Ethiopia

 Tana Lake is the largest lake in Ethiopia. The study published in BMC Veterinary research reported 16.2% prevalence of tapeworm parasite ligula intestinalis infection impacting the health of Labeobarbus species. 

In a cross-sectional study, 384 Labeobarbus fish were collected from February 2023 to March 2024. Out of the 384 Labeobarbus fish examined, 62 tested positives for L. intestinalis, indicating an overall prevalence of 16.2% in Lake Tana. The parasite reported to cause pathological changes including abdominal swelling, gonadal atrophy, organ displacement, body emaciation, and visceral fibrosis accompanied by discoloration. Histological studies indicated altercation in ovaries, the main changes included fibrosis, infiltration of inflammatory cells, destruction, and atrophy of oocytes. Testicular tissues exhibited hyperemia, necrosis, liver vacuolar degeneration and biliary duct hyperplasia. Hence, gross histopathological findings indicated severe lesions in key organs, especially the gonads resulting in impaired reproduction.

The study identified risk factors influencing infection rate, such as fish size, weight , sampling, location and species. Authors noticed that larger and heavier fish are more likely to be infected.

The study reveals that this has a profound impact on the economy and ecosystem. Lake Tana supports both biodiversity and local fisheries. Due to infections, the decline in fish poses danger to food security and livelihood.  The authors have suggested continuous monitoring, awareness program, integrative approaches and ecological interventions to mitigate this challenge.

BMC Zoology - Distribution range and human-hippopotamus (Hippopotamus amphibious) conflict in the Lake Tana biosphere reserve, Ethiopia

Tana Lake is the largest freshwater lake of Ethiopia. Lake Tana Biosphere Reserve (LTBR) is rich in wildlife, both aquatic and terrestrial and vital habitats of biodiversity conservation. A recent study published in BMC Zoology investigated the distribution range and human hippopotamus conflict in LTBR.

The study was conducted between June 22 and January 2023, around 200 individuals participated in the survey. Estimated total mean population of hippopotamus  reported in the LTBR was 252.7 ± 15.9, with density of 0.07 individuals/km². The highest population of hippopotamus was recorded in August and lowest in December.

Employing ARCgis researchers assessed habitat suitability revealing that only 4.7% of shoreline was most suitable for hippopotamuses, 48.4% moderately suitable, and 46.9% unsuitable suitable. Factors that influenced habitat were water availability, vegetation and elevation.

Human hippopotamus conflicts were prevalent primarily due to crop breeding and overgrazing. Local communities reported significant crop damage particularly to maize, sorghum, teff and wheat.  To circumvent this, farmers implemented various strategies such as constructing fences, digging ditches around the crops.

The study advocates the need for sustainable conservation strategies, including habitat protection and community engagement to ensure coexistence of hippopotamus and local communities.

BMC Microbiology - Extreme trophic tales: deciphering bacterial diversity and potential functions in oligotrophic and hypereutrophic lakes

The recent study published in BMC Microbiology explored bacterial diversity and potential function of two lakes in Yunnan Plateau in Southwest China with different nutrient condition. 60 water samples were collected from Lake Fuxian-deep water freshwater (oligotrophic) and shallow Lake Xingyun (hypereutrophic) during different hydrological periods from (April 2020 to January 2021 ). The researcher employed 16srRNA high throughput sequencing to explore distinct community structures and metabolic potentials.

The finding revealed that hyper eutrophic ecosystem exhibited higher α and β diversity compared to oligotrophic ecosystem. Actinobacteria dominated the oligotrophic lake while cyanobacteria , proteobacteria were more prevalent in hypertrophic lake. Additionally, functional analysis indicated that oligotrophic lake bacteria were associated with ethanol oxidation, metalloprotein compartmentation, aromatic compound degradation and  nitrogen respiration underscoring the vital role of bacteria and carbon nitrogen cycle.  In hypereutrophic lake bacteria exhibited function related to ureolysis , human pathogen, animal parasite and symbionts; highlighting human activity related disturbance and potential pathogenic risks.

The study sheds insights into the complex relationship between trophic states and highlighting the significant differences in diversity community composition and network characteristics in oligotrophic  and hyper eutrophic lakes.

BMC Microbiology-Environmental stressors drive fungal community homogenization and diversity loss in plateau freshwater lakes

Fungi has a crucial role to play in aquatic ecosystems. They recycle nutrients, break down organic matter and aid in purifying water. Fungi are known to be exposed to more complex environments in aquatic ecosystems than in terrestrial environments, leading to significant heterogeneity in their abundance across habitats. In the  recent study published in BMC Microbiology, authors carried out study at Three plateau lakes Yunnan Province, China namely Chenghai Lake, Erhai Lake and Lugu Lake.

Plateau lakes represent unique high-altitude ecosystems characterized by distinct physicochemical gradients such as fluctuations in dissolved water, temperature variations and geographical isolation. In the study the Samples were collected from 6 sites, high-throughput sequencing was carried out to understand the influence of geographical and physicochemical factors on fungal communities.

Prominent differences in community structure across the three lakes were observed. Fungal diversity in Chinghai Lake (poor water quality) was significantly lower than in Lugu and Erhai Lakes, and had more homogenized community, the other two lakes displayed greater internal community variation. While each lake maintained unique fungal taxa , only 27.64 % of Operational Taxonomical Unit (OTU) was shared across three lakes.   Altitude, potassium and Ph were prominent physicochemical variables shaping community structure.

Notably, the fungal networks in all three lakes were dominated by positive correlations, with Lugu Lake (83%) exhibiting the highest proportion of positive associations compared to Erhai (62%) and Chenghai (72%) Lakes. The study has aid in understanding the impact of environmental stress can profoundly influence fungal and microbial community, with climate change and further human activities can alter microbial community.