Enrichment of polycyclic aromatic hydrocarbons (PAHs) in mariculture sediments of Hong Kong

Surface and core sediments collected from six fish farms in Hong Kong and from reference sites were investigated for the enrichment and sources of polycyclic aromatic hydrocarbons (PAHs). Moderately high ∑PAH₁₆ levels (123-947 ng g⁻¹, mean: 450 ng g⁻¹) were found in the surface aquaculture sediments. In comparison with the sediments from the reference sites, the average enrichment percentage of total organic carbon (TOC) and PAHs in surface sediments were 21.4 and 43.8%, respectively, and in the core sediments, 24.6 and 73.7%, respectively. Mathematical source apportionment analyses (i.e. isomer ratios, hierarchical cluster analysis, principal components analysis with multiple linear regression analysis) suggested a higher percentage of petrogenic sources in aquaculture sediments. The fish feeds might be the main source of the enriched PAHs in the aquaculture sediments. To our knowledge, this is the first study showing that PAHs in aquaculture sediments could be attributed to human aquaculture activities.     

Occurrence and distribution of antibiotics in coastal water of the Bohai Bay, China: impacts of river discharge and aquaculture activities

The presence of 21 antibiotics in six different groups was investigated in coastal water of the Bohai Bay. Meantime, to illuminate the potential effects caused by the river discharge and aquaculture activities, wastewater from three breeding plants and surface water from six rivers flowing into the Bohai Bay were also analyzed for the selected antibiotics. The result revealed that measured antibiotics in the North Bobai Bay were generally higher than those in the South, highlighting the remarkable effects of high density of human activities on the exposure of antibiotics in environment. The antibiotics found in the six rivers were generally higher than those in the Bohai Bay reflecting the important antibiotics source of river discharge. This study reveals that the high consumption of some antibiotics in aquaculture activities may pose high ecological risk to the bay.     

Evaluating aquacultural use of thermal effluents: An application of system dynamics to environmental problem solving

Given the ecological burden imposed by power plants located in the coastal zone, efforts to improve the marginal benefits realized from their operation are warranted. Indeed, if this source of environmental pollution can be utilized to compensate for past ecological damage, then the benefits will be magnified many-fold.This study addresses the economic feasibility of utilizing heated effluent water from power plants to invigorate the growth of oysters raised under controlled conditions. The preliminary findings indicate that given proper combinations of system capacity, supplemental nutrient supplies, sea water flow and temperature gradients, such an operation is feasible.This is also a demonstration of a viable application of a sophisticated computer modeling approach to environmental problems. System Dynamics a technique pioneered at the Massachusetts Institute of Technology, is applied to evaluate the physical, biological, and economic interrelationships of the aquacultural system variables. It offers many advantages for the environmental manager and researcher, a number of which are realized in the present investigation.     

Energy economy of salmon aquaculture in the Baltic sea

Resource utilization in Atlantic salmon aquaculture in the Baltic Sea was investigated by means of an energy analysis. A comparison was made between cage farming and sea ranching enterprises each with yearly yields of 40 t of Atlantic salmon. A variety of sea ranching options were evaluated, including (a) conventional ranching, (b) ranching employing a delayed release to the sea of young smolts, (c) harvesting salmon both by offshore fishing fleets and as they return to coastal areas, and (d) when offshore fishing is banned, harvesting salmon only as they return to coastal areas where released. Inputs both from natural ecosystems (i.e., fish consumed by ranched salmon while in the sea and raw materials used for producing dry food pellets) and from the economy (i.e., fossil fuels and energy embodied in economic goods and services) were quantified in tonnes for food energy and as direct plus indirect energy cost (embodied energy). The fixed solar energy (estimated as primary production) and the direct and indirect auxiliary energy requirements per unit of fish output were expressed in similar units. Similar quantities of living resources in tonnes per unit of salmon biomass output are required whether the salmon are feeding in the sea or are caged farmed. Cage farming is about 10 times more dependent on auxiliary energies than sea ranching. Sea ranching applying delayed release of smolts is 35–45% more efficient in the use of auxiliary energies than conventional sea ranching and cage farming. Restriction of offshore fishing would make sea ranching 3 to 6.5 times more efficient than cage farming. The fixed solar energy input to Atlantic salmon aquaculture is 4 to 63 times larger than the inputs of auxiliary energy. Thus, cage farming and sea ranching are both heavily dependent on the productivity of natural ecosystems. It is concluded that sustainable development of the aquaculture industry must be founded on ecologically integrated technologies which utilize the free production in marine ecosystems without exhausting or damaging the marine environment.     

Towards Understanding the Impacts of the Pet Food Industry on World Fish and Seafood Supplies

The status of wild capture fisheries has induced many fisheries and conservation scientists to express concerns about the concept of using forage fish after reduction to fishmeal and fish oil, as feed for farmed animals, particularly in aquaculture. However, a very large quantity of forage fish is being also used untransformed (fresh or frozen) globally for other purposes, such as the pet food industry. So far, no attempts have been made to estimate this quantum, and have been omitted in previous fishmeal and fish oil exploitation surveys. On the basis of recently released data on the Australian importation of fresh or frozen fish for the canned cat food industry, here we show that the estimated amount of raw fishery products directly utilized by the cat food industry equates to 2.48 million metric tonnes per year. This estimate, plus the previously reported global fishmeal consumption for the production of dry pet food suggest that 13.5% of the total 39.0 million tonnes of wild caught forage fish is used for purposes other than human food production. This study attempts to bring forth information on the direct use of fresh or frozen forage fish in the pet food sector that appears to have received little attention to this date and that needs to be considered in the global debate on the ethical nature of current practices on the use of forage fish, a limited biological resource.     

Recognize fish as food in policy discourse and development funding

The international development community is off-track from meeting targets for alleviating global malnutrition. Meanwhile, there is growing consensus across scientific disciplines that fish plays a crucial role in food and nutrition security. However, this ‘fish as food’ perspective has yet to translate into policy and development funding priorities. We argue that the traditional framing of fish as a natural resource emphasizes economic development and biodiversity conservation objectives, whereas situating fish within a food systems perspective can lead to innovative policies and investments that promote nutrition-sensitive and socially equitable capture fisheries and aquaculture. This paper highlights four pillars of research needs and policy directions toward this end. Ultimately, recognizing and working to enhance the role of fish in alleviating hunger and malnutrition can provide an additional long-term development incentive, beyond revenue generation and biodiversity conservation, for governments, international development organizations, and society more broadly to invest in the sustainability of capture fisheries and aquaculture.Electronic supplementary materialThe online version of this article (10.1007/s13280-020-01451-4) contains supplementary material, which is available to authorized users.     

Assessing the carrying capacity of tilapia in an intertidal mangrove-based polyculture system of Pearl River Delta, China

A trophic model of an intertidal mangrove-based polyculture system in Pearl River Delta, China, was constructed using the Ecopath with Ecosim software. This polyculture system was chosen since it is the first integrated multi-trophic aquaculture (IMTA) system that was constructed on the basis of mangrove planting in China. The energy flows, ecosystem property, and carrying capacity of tilapia in the polyculture system were analyzed and evaluated. The results show the trophic level of 1.00 for primary producers and detritus to 2.85 for grass carp. The geometric mean of the trophic transfer efficiencies was 7.0%, with 7.2% from detritus and 6.8% from primary producers within the system. The ecosystem property indices show that this polyculture system has a high value of total primary production/total respiration (TPP/TR) and total primary production/total biomass (TPP/TB), together with low Finn's cycled index (FCI), Finn's mean path length (FML), and connectance index (CI), indicating that this system is at a development stage according to Odum's theory. The principal fish cultured in the system is tilapia, and mixed trophic impacts (MTI) show that tilapia has a marked impact on most compartments in this system, and the carrying capacity was found to be a tilapia culture biomass of 5.8 t ha⁻¹ in the system.     

江蓠生长对甲壳素废水的净化作用

探索小型水泥池中甲壳素废水对江蓠生长的影响以及江蓠生长对甲壳素废水的净化作用，在1m^3水泥池中放养100g长度为5cm的江蓠，充气并加入不同比例的甲壳素废水，平行2组；加入同一比例甲壳素废水，以不同温度进行处理，平行1组。结果表明：在10：1的甲壳素废水中，江蓠生长的适宜温度为26℃左右；甲壳素废水的浓度影响江蓠的生长率，第10d时，添加10：2的浓度有效高的生长率；江蓠在浓度为10：10废水的生长过程中，第3d对CODCr、BOD5去除率最佳，分别为65．8％、52．1％。通过江蓠生长与自然条件下的废水净化效果的比较，江蓠的正常生长能使甲壳素废水达到排放标准。     

Dynamic emergy evaluation of a fish farm rearing process

The environmental sustainability of a fish farm rearing process was examined by means of emergy analysis. Many emergy analyses integrate data for a whole year smoothing short term variations and sometimes losing meaningful information (aliasing). For this reason we developed a model for an instantaneous emergy evaluation in an aquacultural system so that transformities, efficiency and effort spent at each moment during the fish rearing activity could be calculated. By means of the model and dynamic emergy calculations it is possible to recognize step by step the importance of the various emergy contributions and verify where and when to modify the system to move toward optimum production of a sustainable product. By the application of the model we confirmed that the emergy trends in a fish farm installation follow wide oscillations during a year due to variations in both internal and external emergy contributions. Among the fluxes considered, those due to the introduction of fingerlings represented the highest contributions to the total emergy budget. Thus, to improve the sustainability of the analyzed system the amount, frequency and timing of these fluxes must be carefully considered. For this purpose, a comparison between two different fry introduction schedules was performed to evaluate differences in the efficiency of the rearing process.     

Electrochemical removal of ammonium nitrogen in high efficiency and N2 selectivity using non-noble single-atomic iron catalyst

Ammonia nitrogen (NH₄⁺-N) is a ubiquitous environmental pollutant, especially in offshore aquaculture systems. Electrochemical oxidation is very promising to remove NH₄⁺-N, but suffers from the use of precious metals anodes. In this work, a robust and cheap electrocatalyst, iron single-atoms distributed in nitrogen-doped carbon (Fe-SAs/N-C), was developed for electrochemical removal of NH₄⁺-N from in wastewater containing chloride. The Fe-SAs/N-C catalyst exhibited superior activity than that of iron nanoparticles loaded carbon (Fe-NPs/N-C), unmodified carbon and conventional Ti/IrO₂-TiO₂-RuO₂ electrodes. And high removal efficiency (> 99%) could be achieved as well as high N₂ selectivity (99.5%) at low current density. Further experiments and density functional theory (DFT) calculations demonstrated the indispensable role of single-atom iron in the promoted generation of chloride derived species for efficient removal of NH₄⁺-N. This study provides promising inexpensive catalysts for NH₄⁺-N removal in aquaculture wastewater.