Silver Lake

Shengnan Yin, C. Tong

M. Kirby, E. Knell, W. Anderson, M. Lachniet, J. Palermo, H. Eeg, R. Lucero, R. Murrieta, A. Arevalo, E. Silveira, C. Hiner

M. Parish, K. Wolf, P. Higuera, B. Shuman

Abstract The wettest portion of the interior of western North America centers on the mountainous region spanning western Montana, Idaho, British Columbia, and Alberta. Inland ranges there capture the remnants of Pacific storms. Steep east–west hydroclimate gradients make the region sensitive to changes in inland-penetrating moisture that may have varied greatly during the Holocene. To investigate potential hydroclimate change, we produced a 7600-yr lake-level reconstruction from Silver Lake, located on the Montana–Idaho border. Ground-penetrating radar profiles and a transect of four shallow-water sediment cores that were dated using radiocarbon dating and tephrachronology revealed substantial changes in moisture through time. An organic-rich mud unit indicating wet and similar to modern conditions prior to 7000 cal yr BP is overlain by an erosional surface signifying drier than modern conditions from 7000–2800 cal yr BP. A subsequent time-transgressive increase in water levels from 2800–2300 cal yr BP is indicated by a layer of late Holocene muds, and is consistent with glacier expansion and increases in the abundance of mesic tree taxa in the region. Millennial-scale trends were likely driven by variations in orbital-scale forcing during the Holocene, but the regional outcomes probably depended upon factors such as the strength of the Aleutian Low, Pacific sea-surface temperature variability, and the frequency of atmospheric rivers over western North America.

Dan Zhou, Ting Zhang, Long Ren, Di’an Fang, Dongpo Xu

Both fish gills and guts can support lots of microbiota that play important roles in the health and growth of hosts. Although the microbiota of silver carp has been widely studied, the data on microbial variation according to fish tissues and local habitats are lacking. In this study, the microbes in the guts and gills of silver carp (Hypophthalmichthys molitrix) from the hydrophyte-dominated region (zone H) and the algae-dominated region (zone A) of Taihu Lake in autumn were analyzed. Proteobacteria, Cyanobacteria, and Firmicutes were the dominant bacteria in silver carp. The microbial diversity was higher in the gills than that in the intestines, and higher in fish from zone H than that from zone A. Beta diversity analysis revealed significant differences in microbial community structures between gill and guts, and between fish from the two habitats. Gills had a higher abundance of phyla Actinobacteria, Bacteroidetes, and Deinococcus-Thermus, and a lower abundance of verrucomicrobia than the intestine. Both tissues possessed indicator taxa, while many indicator taxa in the gill were conditional pathogens. Compared to fish from zone H, fish from zone A had more abundant Cyanobacteria, and less abundant Proteobacteria and Bacteroidetes. PICRUSt2 analysis revealed that fish microbial functions were mainly associated with metabolism, replication, repair, folding, sorting, and degradation. These results showed that the microbial community of silver carp from Taihu Lake varied according to tissues and habitats.

Claudious Gufe, Bothwell Karembera, Jerikias Marumure, Z. Makuvara

Abstract Antibiotic and heavy metal-resistant pathogenic bacteria associated with fish from contaminated water can spread diseases. This study aims to identify antibiotics, lead, and silver nitrate-resistant bacteria in 180 fish samples from Lake Chivero using bacterial identification, disk-diffusion, and agar dilution methodologies. Of the identified 157 bacterial isolates, 46 (29.3%) were Staphylococcus, 35 (22.3%) were Escherichia coli, 26 (16.6%) were Aeromonas spp., 15 (9.6%) were Shigella spp., 13 (8.3%) were Bacillus cereus, 12 (7.6%) were Edwardsiella tarda, 7 (4.5%) were Proteus mirabilis, and 3 (1.9%) were Listeria spp. Gentamicin was the most effective, with 100% of the bacterial species susceptible, followed by neomycin (68.2%), tetracycline (56.7%), cloxacillin (52.2%), streptomycin (51%), erythromycin (32.6%), lincomycin (15.3%), and rifampicin (13.4%). For the eight taxa investigated, the multiple antibiotic resistance (MAR) index ranged from 0.50 to 0.88, with all values greater than 0.2. E. Coli and Proteus spp. had the highest MAR index values (0.88 each), followed by Bacillus, Aeromonas, and Staphylococcus (0.75 each), and Listeria, Edwardsiella, and Shigella (0.63 each). The isolated bacteria were multidrug-resistant, with varying resistance levels to lead and silver nitrate, with silver nitrate resistance rates ranging from 23.1–88.5% and lead resistance rates ranging from 30.8–69.2%. The multidrug resistance (MDR) pathogenic bacteria are found in fish from contaminated Lake Chivero, posing a health risk to humans. As a result, adequate waste disposal is required, as is multi-sectoral monitoring of antimicrobial resistance (AMR) and public education about the health risks associated with fish and fish-derived products.