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International audience; For the last two decades, a rapid eutrophication process impacts Lake Titicaca, the largest tropical freshwater lake in South America and the main highest Great Lake. This is especially notorious in the Bolivian sector of its shallow Lago Menor sub-basin. Lago Menor is deteriorated by the combination of multiple contaminations (domestic, industrial and mining) from untreated wastewater discharged from the urban area of El Alto, indiscriminate overfishing, and climate change. These threats particularly affect the native Andean killifish genus Orestias, the ecology and dynamics of which require in-depth studies with non-invasive techniques. Here, we use hydroacoustic method to evaluate fish patterns of distribution and abundance in the Lago Menor. Hydroacoustic data were collected during the 2015 rainy season (November) with vertical beaming at 120 kHz along transects that sum a total length of 140 km. Our results showed that the proxy of fish biomass was linked to Lago Menor bathymetry. Furthermore, the vertical fish biomass proxy was steady from 3 to 20 m. This pilot study provides the first image of fish, mostly Orestias spp., distribution and opens future studies to deepen knowledge on their ecology and ethology, and regular monitoring of their population and stock for the fisheries assessment in Lake Titicaca.

International audience

Tropical high-altitude Andean lakes are physically harsh ecosystems. Located above the treeline (>= 4000 m a.s.l.), they share common features with temperate alpine lakes, which impose extreme conditions on their aquatic organisms: e. g., strong winds, broad diel variations in water temperature, and intense solar ultraviolet radiation (UVR). However, because of their latitude, they differ in two major ecological characteristics: they lack ice cover during the winter and they do not present summer water column stratification. We sampled 26 tropical high-altitude Andean lakes from three regions of the Bolivian Eastern Andes Cordillera during the wet period (austral summer). We performed an ordination to better describe the typology of Andean lakes in relation to the environmental variables, and we assessed the relationships among them, focussing on the UV-A transparency (360 nm) throughout the water column. We found a positive correlation between UV-A transparency calculated as Z(1%) (the depth which reaches 1% of the surface UV-A), the lake maximum depth and Secchi transparency (r = 0.61). Z(1%) of UV-A was smaller in shallow lakes than in deep lakes, indicating that shallow lakes are less transparent to UV-A than deep lakes. We hypothesize that, compared to shallow lakes, deep lakes (maximum depth > 10 m) may have lower dissolved organic carbon (DOC) concentrations (that absorb UV radiation) due to lower temperature and reduced macrophyte cover. Based on our data, tropical high-altitude Andean lakes are less transparent to UV-A (K-d range = 1.4-11.0 m (1); Z(1%) depth range = 0.4-3.2 m) than typical temperate alpine lakes (1-6 m (1), 3-45 m, respectively). Moreover, they differ in vertical profiles of UV-A, chlorophyll-a, and temperature, suggesting that they may have a distinct ecological functioning. Such peculiarities justify treating tropical high-altitude Andean lakes as a separate category of alpine lakes. Tropical high-altitude Andean lakes have been poorly studied. Thus they deserve more in-depth studies in the face of global changes regarding the use of their UV transparency as a sentinel proxy of climate changes, particularly global warming.

International audience

Analisou-se o crescimento dos peixes, a composição das espécies e a produtividade de quatro policultivos (P75, P78, P87 e P207), visando melhorar o manejo e a produtividade pesqueira dos pequenos açudes (0,1-5,0ha) do Semi-Árido brasileiro. Simulou-se as condições desses açudes em viveiros com 120 e 5.000 m² de área, sem renovação de água, utilizando moderada quantidade de adubo e fertilizante. A biomassa inicial variou de 75 a 207kg ha-1, sendo formada por: tilápia do Nilo (Oreochromis niloticus), curimatã pacu (Prochilodus argenteus), carpa comum (Cyprinus carpio), tambaqui (Colossoma macropomum) e tucunaré (Cichla ocellaris). Os peixes apresentaram baixo crescimento (< 0,01g g-1 d-1) após 75 dias de criação (P78 e 87). O crescimento do tambaqui, da tilápia e da curimatã foi reduzido após 53 dias (P75). Em moderada biomassa, o crescimento do tambaqui foi inferior ao da carpa e da curimatã (P207). A produtividade da tilápia atingiu 720 kg ha-1ano-1 (P78), sendo reduzida para 220 kg ha-1ano-1 devido ao processo reprodutivo (P75 e P207). A produtividade da carpa de 1.600 kg ha-1ano-1 foi superior a dos outros peixes (P87). A biomassa inicial de 75 kg ha-1 (60:30:4:3:3% de tilápia, tambaqui, carpa, curimatã e tucunaré, respectivamente) otimizou o crescimento e a produtividade dos peixes. A utilização de tilápias monossexadas e o fornecimento da alimentação suplementar ao tambaqui tornam-se imprescindíveis ao policultivo. The analysed species composition, fish growth, and productivity of four polycultures (P75, P78, P87, and P207) with the objective to improve the small reservoir (0.1-5 ha) fishery management and productivity in the Brazilian semiarid region were conducted a experiment. To mimic reservoir conditions, we used 120 and 5,000m² ponds and evaporation and infiltration water loss was replaced. In addition, manure and fertilizers were used only moderately. The initial biomass of Nile tilapia Oreochromis niloticus, 'tambaqui' Colossoma macropomum, 'curimatã pacu' Prochilodus argenteus, common carp Cyprinus carpio, and 'tucunaré' Cichla ocellaris ranged from 75 to 207kg ha-1. The fish showed low growth rates (

Les auteurs ont quantifié les incidences de la biomasse et du type de planctophage dans le cadre d'une étude expérimentale en mésocosmes. Cette étude était conçue en fonction d'un plan factoriel d'expérience combinant cinq niveaux de biomasse de poisson (de O, à 75 g/m3) avec deux types de planctophage, soit l'alose à gésier (#Dorosoma cepedianum$), un filtreur, et le crapet arlequin (#Lepomis macrochirus$), un chasseur visuel. Une augmentation de la biomasse de poisson était accompagnée d'une baisse du nombre de cladocères, de cyclopoïdes et de chironomides et de la teneur en phosphore particulaire ...; inversement l'abondance de rotifères, de flagellés unicellulaires, d'algues vertes coloniales et unicellulaires, de diatomées pennées, la productivité primaire, la turbidité et les teneurs en chlorophylle a, en phosphore total ... ont augmenté ... Bien que la chaîne des cascades trophiques de l'alose à gésier et celle du crapet soleil soient différentes, la biomasse de poisson jouait un rôle plus important que le type de planctophage comme régulateur des communautés planctoniques et de la qualité de l'eau. (D'après résumé d'auteur)