Impacts of Nile tilapia cage culture on water and bottom sediment quality: The ability of an eutrophic lake to absorb and dilute perturbations

Environmentally sustainable aquaculture depends on accurate understanding of the impacts of aquaculture-derived organic matter (AOM) and the ability of aquaculture systems to absorb and dilute perturbations. To this end, the present study assessed the impacts of AOM from cage culture of Nile tilapia on the ecology of Lake Victoria, Kenya, using fish cages near Anyanga Beach in Siaya County from December 2018 to October 2019. Four locations were surveyed for organic loadings from cage cultures, located 0, 50, 150 and 500 m (as a control site) away from the cages. The cage aquaculture produced increased P and N concentrations near the cages and a decreased N:P molar ratio. These changes stimulated algal growth which, in turn, affected the water quality. The organic material accumulated on the bottom under the cages, increasing the benthic BOD (BOD, >10 mg/g), a sensitive indicator of the ecological footprint of the cage aquaculture. Further, the negative ORP observed in the benthic layer suggested anoxic bacterial metabolism, possibly causing build-up of sulphides and methane. These changes altered the abundance and composition of both limnetic and benthic communities. At the beginning of the study, 22 zoobenthic taxa existed around the cages and 18 at the reference sites. Only 3 saprophilous taxa, chiefly gastropods (Physella spp.), bivalves (Sphaerium spp.) and oligochaetes (Tubifex spp.) were present at the cage site and 17 at the reference site at the end of the culture period. The Shannon diversity index exhibited a declining tendency with the length of culture period at the cage site, signifying a negative impact of aquaculture on biodiversity. The water quality recovery after cage disturbance is rapid (<4 months), noting there was no significant difference in the water quality recorded at the cage site and the other sampling sites after a fallow period of 4 months. However, the recovery of the sediment and meiofauna was far from complete at the end of this period. Moving the cages slightly (50–100 m) away from the former location may allow the benthic communities to recover and alleviate the problem. Further, the fallowing period, particularly for the Anyanga Beach site, should be extended from four to at least 5 months to allow for the environment to recover. With the rapid increase of cage fish farming in the African Great Lakes Region and with the potential for its occurrence in other lakes, there is a need to develop regulations to guide the industry, as well as the need for continuous monitoring of the environment, in order to provide information to guide investments and ensure sustainable cage farming

Enhancing the value of small fish species for food and nutrition security through improved drying and packaging

Drying is affordable preservation method used where poorly developed logistics limit marketing of fresh fish. In Eastern Africa dried Rastrineobola argentea (Dagaa) is an important source of low cost stable dietary protein. The fishery is characterized by high post-harvest losses and products are often of low quality, restricting the sales to low income groups shopping in open-air markets. This study aimed at improving the quality of dried small fish and determines the marketing potential of improved dried Dagaa and industrially dried capelin as new products where traditionally dried small fish are commonly found. The influence of drying and packaging methods on lipid degradation, sensory properties and microbial quality of products during storage was assessed, as well as the marketing potential of dagaa and capelin dried under more hygienic conditions. Drying under controlled conditions improved quality, and when atmospheric oxygen was excluded by vacuum packaging, dried fish became more stable during storage with less lipid degradation, less rancid odor and lower counts of microbes. The products obtained high acceptability ratings, indicating there is market potential for improved dried dagaa and capelin among consumers of traditional dried small fish. The results from this study show that well processed and could contribute to food and nutrition security. Keywords: Dagaa, capelin, drying, quality, acceptabilit

Thermal-Induced Autolysis Enzymes Inactivation, Protein Degradation and Physical Properties of Sea Cucumber, Cucumaria frondosa

Funding Information: Funding: This work was supported by the Fisheries Training Programme of United Nations University (UNU-FTP2017), Research and Demonstration of Efficient Clean Production Mode of Important Marine Fish in Liaoning Province (2020JH1/10200002), National Key R&D Program of China (2019YFD0901800), Project of Education Department of Liaoning Province (JL202011), Project of Ocean and Fisheries Department of Liaoning Province (201722), Key Laboratory of Environment Controlled Aquaculture (Dalian Ocean University) Ministry of Education (202203); National Key R&D Program of China (2020YFD0900600). Funding Information: Acknowledgments: The authors would like to express their heartfelt gratitude to United Nations University Fisheries Training Programme (now GRÓ Fisheries Training Programme, United Nations Education, Scientific and Cultural Organization) and Matis for supporting this research. Special thanks go to Tumi Tomasson, Thor Asgeirsson, Mary Frances Davidson, Julie Ingham, Stefan Ulfarsson, and Lilja Bjork Jonsdottir, for their enthusiastic guidance and assistance during the experiment. Publisher Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland.The main objective is to effectively denature the autolysis enzymes of C. frondosa on the premise of avoiding the quality deterioration caused by overheating. The effects of the different thermal treatments (blanching at 40–80◦ C for 45 min, boiling and steaming at 100◦ C for 15–120 min) on the cooking yield, moisture content, protein degradation, texture, and enzyme inactivation were studied, and the inner relationship was investigated by multivariate analysis. The autolysis enzymes of C. frondosa were thermally stable and cannot be denatured completely by blanching. Boiling and steaming could efficiently inactivate the enzymes but overheating for 60–120 min reduced the cooking yield and texture quality. Boiling at 100◦ C for 45 min was suitable for pre-treatment, with cooking yield of 70.3% and protein content of 78.5%. Steaming at 100◦ C for at least 30 min was preferable for long-term storage and instant food, in which the relative activity was only 3.2% with better palatability.Peer reviewe

A comparative study of the effects of pelleted and extruded feed on growth, financial revenue and nutrient loading of Nile tilapia (Oreochromis niloticus L.) cage culture in a lacustrine environment

We compared the benefits of using extruded feed (EF), against pelleted feed (PF) to guide cage culture investments in Great Lakes. Three out of six cages in the same farm had fish that were fed EF and the other half, belonging to a different farm had fish that were fed PF. The diets were similar in crude protein, lipid and energy content. However, the fiber content in PF was 4 times higher than that of EF. The fish fed on EF grew better (438.0 ± 7.4 g) than the fish fed on PF (220.8 ± 2.9 g). The cost of production for EF was about 26% lower than for PF, primarily because of better feed utilization. The load of P and N for PF diet was 59% and 29% higher, respectively, than when EF was used. Therefore, EF feed delivered better economic gains with lower environmental impact than PF feed

Simulating Trade-offs Between Socio-economic and Conservation Objectives for Lake Victoria (East Africa) Using Multispecies, Multifleet Ecosystem Models

Most small scale inland fisheries worldwide are open access, and fishing provides the only source of employment and livelihood for the riparian communities. Management of these fisheries requires information on trade-offs between fish production, profits from fishing, employment, and conservation objectives. We use the non-linear optimization procedure in Ecopath with Ecosim (EwE) modelling package to determine long-term, gear-specific fishing effort that can maximize economic, social, and conservation objectives for Lake Victoria (East Africa). Then, the resulting “optimal fishing effort” levels are applied in both EwE and Atlantis models to simulate long-term changes in the ecosystem. Results show profit maximization to be more compatible with conservation objectives than is the maximization of catch (or employment). However, maximizing economic value, while maintaining ecosystem structure, would require a reduction in fishing effort of almost every fishing gear. This trade-off can be severe (high social cost) for fishing communities with limited alternative livelihoods. This study provides an understanding of relative risks and benefits of various management objectives, which will enable stakeholders and the public to conduct informed discussions on future management policies

Ecosystem Modelling of Data-limited Fisheries: How Reliable are Ecopath with Ecosim Models without Historical Time Series Fitting?

Long-term time series data are not available for many of the African Great Lakes. This precludes fitting ecosystem model parameters to time series data, and we do not know how reliable non-fitted models are compared to fitted ones in terms of predicting consequences of alternative management strategies. To investigate this, we generate a historical Ecopath with Ecosim (EwE) model for Lake Victoria (East Africa), fitted to time series data (1980–2015), and a present-day EwE model (representing average conditions for the period 2010–2015). We do scenario simulations using the present-day model and the comparable 2015 end-state of the historical model, and test if incorporating information on short-term biomass trends by adjusting biomass accumulation (BA) parameter in the present-day model increases its reliability. We find that there are differences in model predictions, but those differences can be lessened by adjusting BA terms in the present-day model to reflect biomass trends from short-term empirical data. We also compare the models with and without fitted vulnerability parameters. The models generally give comparable results for the dominant commercial fisheries at low fishing pressure; when fishing mortality is increased, the models give variable predictions. This study adds to the current understanding of the limitations of EwE models that are not challenged to reproduce long-term historical fishery responses to perturbations. We conclude that for the less productive groups, as well as groups that suffer heavy mortality (either due to predation or fisheries), it may be appropriate to use negative BA as first draft assumption in present-day models

Ecosystem Models of Lake Victoria (East Africa): Exploring the Sensitivity of Ecosystem Effects of Fishing to Model Choice

Ecosystem simulation models are valuable tools for strengthening and promoting ecosystem-based fisheries management (EBFM). However, utility of these models in practical fisheries management is often undermined by lack of simple means to test the effect of uncertainty on model outputs. Recently, the use of multiple ecosystem models has been recommended as an ‘insurance’ against effects of uncertainty that comes with modelling complex systems. The assumption is that if models with different structure and formulation give consistent results, then, policy prescriptions are robust (i.e. less sensitive to model choice). However, information on the behaviour of trends from structurally-distinct ecosystem models with respect to changes in fishing conditions is limited, especially for freshwater systems. In this study, we compared outputs of two ecosystem models, Ecopath with Ecosim (EwE) and Atlantis, for Lake Victoria under different fishing pressure scenarios. We compared model behaviour at the ecosystem level, and also at a level of functional groups. At functional group level, we determined two questions: what is the change in the targeted group, and what are the consequent effects in other parts of the system? Overall results suggest that different model formulations can provide similar qualitative predictions (direction of change), especially for targeted groups with similar trophic interactions and adequate data for parameterization and calibration. However, considerable variations in predictions (where models predict opposite trends) may also occur due to inconsistencies in the strength of the aggregate multispecies interactions between species and models, and not necessarily due to model detail and complexity. Therefore, with more information and data, especially on diet, and comparable representation of feeding interactions across models, ecosystem models with distinct structure and formulation can give consistent policy evaluations for most biological groups

Ecosystem Models of Lake Victoria (East Africa): Exploring the Sensitivity of Ecosystem Effects of Fishing to Model Choice

Ecosystem simulation models are valuable tools for strengthening and promoting ecosystem-based fisheries management (EBFM). However, utility of these models in practical fisheries management is often undermined by lack of simple means to test the effect of uncertainty on model outputs. Recently, the use of multiple ecosystem models has been recommended as an ‘insurance’ against effects of uncertainty that comes with modelling complex systems. The assumption is that if models with different structure and formulation give consistent results, then, policy prescriptions are robust (i.e. less sensitive to model choice). However, information on the behaviour of trends from structurally-distinct ecosystem models with respect to changes in fishing conditions is limited, especially for freshwater systems. In this study, we compared outputs of two ecosystem models, Ecopath with Ecosim (EwE) and Atlantis, for Lake Victoria under different fishing pressure scenarios. We compared model behaviour at the ecosystem level, and also at a level of functional groups. At functional group level, we determined two questions: what is the change in the targeted group, and what are the consequent effects in other parts of the system? Overall results suggest that different model formulations can provide similar qualitative predictions (direction of change), especially for targeted groups with similar trophic interactions and adequate data for parameterization and calibration. However, considerable variations in predictions (where models predict opposite trends) may also occur due to inconsistencies in the strength of the aggregate multispecies interactions between species and models, and not necessarily due to model detail and complexity. Therefore, with more information and data, especially on diet, and comparable representation of feeding interactions across models, ecosystem models with distinct structure and formulation can give consistent policy evaluations for most biological groups

Simulation of Lake Victoria Circulation Patterns Using the Regional Ocean Modeling System (ROMS)

<div><p>Lake Victoria provides important ecosystem services including transport, water for domestic and industrial uses and fisheries to about 33 million inhabitants in three East African countries. The lake plays an important role in modulating regional climate. Its thermodynamics and hydrodynamics are also influenced by prevailing climatic and weather conditions on diel, seasonal and annual scales. However, information on water temperature and circulation in the lake is limited in space and time. We use a Regional Oceanographic Model System (ROMS) to simulate these processes from 1^st January 2000 to 31^st December 2014. The model is based on real bathymetry, river runoff and atmospheric forcing data using the bulk flux algorithm. Simulations show that the water column exhibits annual cycles of thermo-stratification (September–May) and mixing (June–August). Surface water currents take different patterns ranging from a lake-wide northward flow to gyres that vary in size and number. An under flow exists that leads to the formation of upwelling and downwelling regions. Current velocities are highest at the center of the lake and on the western inshore waters indicating enhanced water circulation in those areas. However, there is little exchange of water between the major gulfs (especially Nyanza) and the open lake, a factor that could be responsible for the different water quality reported in those regions. Findings of the present study enhance understanding of the physical processes (temperature and currents) that have an effect on diel, seasonal, and annual variations in stratification, vertical mixing, inshore—offshore exchanges and fluxes of nutrients that ultimately influence the biotic distribution and trophic structure. For instance information on areas/timing of upwelling and vertical mixing obtained from this study will help predict locations/seasons of high primary production and ultimately fisheries productivity in Lake Victoria.</p></div