We examine phytoplankton community structure and how it is influenced by commercial tilapia (Oreochromis niloticus L.) cage farming in three tropical lakes in eastern Brazil. Sampling occurred during both the wet and dry seasons for two treatments-within tilapia cages and outside the cages in the lake. Total ammonia, total phosphorus, chlorophyll a, phycocyanin and phytoplankton were measured in all water samples. In the phytoplankton community, we estimated species richness and total abundance. Thirty-three genera of algae distributed in 8 classes were identified. The most abundant classes were Chlorophyceae and Cyanophyceae (the latter of which was the most species-rich class). In Palmas Lake, chlorophyll a was constant over time (summer and winter) and location (within and outside cage farms), which may reflect the fact that fish farming is more recent in this lake. The richness and abundance of species were similar among the lakes, but Palminhas Lake tended to have more extreme values, apparently associated with the longer time fish have been farmed there. Fish farming clearly influences water quality as measured by algae species richness and abundance but is also moderated by the unique conditions in each lake and the amount of time over which the fish have been farmed. Understanding and preventing the impacts and detrimental consequences of tilapia cage farming on both the farming yield and the water quality in tropical lakes require continual monitoring.
Oxygen and temperature are the most limiting factors in aquatic environments. Several species are exposed to variations of these factors in water because of physical, chemical and biological processes. The objective of this study was to evaluate the metabolic profile and the tolerance to the hypoxia of Geophagus brasiliensis exposed to changes in temperature and oxygen availability. The fish were exposed to 20 and 90% of oxygen saturation combined with different temperatures (20°, 24° and 28° C) for 8 h. Hepatic and muscular glycogen, as well as the activities of lactate dehydrogenase (LDH), malate dehydrogenase (MDH), citrate synthase (CS) and their ratios were evaluated. Both glycogen and MDH activity showed a significant difference in the liver. While CS showed increased activity only in the heart. The increase in LDH activity in the white muscle shows the importance of the anaerobic pathway as energy source in this tissue. The MDH / LDH ratio increased in all tissues, while CS / LDH increased in the liver and decreased in the heart. Based on the results of the present study it may be concluded that this species used the anaerobic metabolism as the main strategy for hypoxia tolerance.
Cage fish farming in natural and artificial lakes has become increasingly popular in recent years in tropical countries. The most commonly farmed tropical fish species is the Nile tilapia (Oreochromis niloticus L.). The aim of this study was to characterize the concentration of phosphorus, total ammonia nitrogen and chlorophyll a from existing fish farms (FF) in Lake Palminhas, located in Linhares/ES, Brazil. Three transects were drawn from 0 to 500 m from each of the four FF (FF1 to FF4) in the lake during six trials (three in the rainy season and three in the dry season). The lake presented a monomictic-hot pattern, with stratification during the rainy season. Dilution of the monitored parameters did not occur sufficient over a distance of up to 500 m from the FF. The location of the FF in the lake and the input of N and P were critical to ensure optimal mixing conditions because the worst results was observed for the fish farm (FF1) located on a finger of the lake, where the highest concentrations of total phosphorus and chlorophyll a occurred. It was also noted that there was possible total phosphorus interference between FF3 and FF4. The results of this study demonstrate that Lake Palminhas had a low dilution power, and these findings may inform environmental assessments of cage fish farming in this region, providing instruments that may support environmental control of cage fish farming.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
334 Leonard St
Brooklyn, NY 11211
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.