Browsing by Subject "Eutrophication"

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Development of highly digestible fish feeds from locally available resources in Iran
(2025) Salehi, Hamed; Focken, Ulfert
In 2012, global aquaculture production (excluding aquatic plants) was 63.5 million tons, increasing to 94.4 million tons by 2022—a growth of 48%. In Iran, production rose by 62% during the same period, from 296,514 to 480,624 tons. Iran is a leading producer of rainbow trout (Oncorhynchus mykiss W.), contributing 15-21% of the global supply from 2012 to 2022. However, aquafeed, which accounts for 70% of production costs and 80% of environmental effluents, has been impacted by a decline in fish meal production in 2023. This may increase costs, especially for carnivorous species like rainbow trout, necessitating alternative protein sources. Currently, canola meal, a potential plant-based protein, is not widely used in Iran due to poor utilization by fish. Furthermore, local poultry by-products are viewed as low-quality protein sources compared to those in countries like Germany, due to a lack of processing technologies, which restricts their utilization in aquafeed industry. Therefore, some of these products like blood and feather meals are realised not comparable to fish meal in feeding rainbow trout for the aquafeed industry in Iran. Nutrient eutrophication in water bodies necessitates development of environmentally friendly aquafeed out of highly-digestible feed components, as well. Therefore, this research was conducted to assess the digestibility of various feed components, including poultry by-products such as PBM, BM, FeM, PPCon and plant-based proteins like CM and SBM, in rainbow trout. The test ingredients were incorporated into a semi-purified casein-based diet at a 30:70 ratio, with TiO₂ used as a marker, and then fed to the experimental fish. Feces were collected using the settling method in 57-liter aquaria. The apparent protein digestibility coefficients for PBM, FeM, PPCon, BM, CM, and SBM were 73%–93%, 73%–96%, 100%, 87%, 94%, and 97%, respectively. The most digestible feed components in terms of CP were chosen to create five fish-meal-free diets, with increasing levels of CM ranging from 20% to 40%, to compare with a casein-based diet in terms of growth performance and apparent digestibility in juvenile rainbow trout. Subsequently, the 35% CM diet, which achieved the least cost FCR, was slightly modified and extruded to feed fattening rainbow trout in tanks. This diet was then compared to a pelleted caseinbased diet to assess growth performance and nutrient effluents in tanks and simultaneously, the assessment of CP, CL,OMdigestibility as well as the availability of P in juvenile rainbow trout in aquaria set-up using the settling method. This extruded grow-out feed, which included 35% CM and approximately 32% highly digestible poultry by-products, proved to be comparable to the highly digestible semi-purified casein-based diet in terms of supporting growth performance and body criteria in rainbow trout. The utilization of macronutrients like CL, CP, and OM in this extruded feed was remarkably similar to that of the control feed (p>0.05). However, the P load from this practical diet was higher in the water compared to the control feed (p<0.05). This issue could potentially be addressed by lowering the phosphorus concentration in the feed for fish of that size and considering the phosphorus availability of each component used in the diet. This investigation showed that when terrestrial protein sources are properly combined to provide all essential nutrients to the fish, feeds without FM can not only promote high growth performance but also enable efficient nutrient utilization in rainbow trout. Lastly, properly processed poultry by-products can serve as valuable protein sources for the growing aquafeed industry in developing countries like Iran.
Spatio-temporal water quality determines algal bloom occurrence and possibly lesser flamingo (Phoeniconaias minor) presence in Momella lakes, Tanzania
(2022) Lihepanyama, Deogratias Ladislaus; Ndakidemi, Patrick Alois; Treydte, Anna Christina
Eutrophication and algal blooms have sparked worldwide concern because of their widespread effects on water-dependent species. Harmful algal blooms can cause fatal effects to lesser flamingos (Phoeniconaias minor), obligatory filter feeders and vital bio-indicators in soda lakes. Thus, early detection of algal blooms and potential indicators in water quality is critical, but general tools are lacking in eastern African soda lakes. We monitored algal biomass changes and related water physico–chemical variables for 12 consecutive months in the lakes Big Momella and Rishateni in northern Tanzania. We used chlorophyll-a to measure algal biomass and quantified water physico–chemical variables that might influence algae growth. We also monitored lesser flamingo numbers to understand trends across the year and according to algal bloom occurrence. Algal biomass was strongly related to water nitrogen (r = 0.867; p < 0.001) and phosphorus (r = 0.832; p < 0.001). Monthly patterns showed significant differences in water quality and algal biomass (F = 277, p < 0.001) but not across sampling sites (F = 0.029, p = 0.971). Lesser flamingo numbers seemed to be related to algal biomass at Lake Big Momella (r = 0.828; p < 0.001) and shortly after algal biomass peaked high (i.e., March and April 2021), flamingo numbers declined. Lake Rishateni showed similar patterns. Our findings can provide a basis towards understanding the factors contributing to temporal changes in lesser flamingo abundance due to spatio–temporal water quality variations, which is important for optimising conservation efforts for the species in these unique Momella lakes.