Total nitrogen,carbon and phosphorus digestibility in gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax) fed with conventional and organic commercial feeds: implications for particulate waste production

Organic fish farming is postulated as a more environmentally friendly activity than conventional activities. However, environmental sustainability as regards waste output has not been addressed. In this respect, the most important environmental problems associated with fish farming are those related with the discharge of particulate wastes. In this study, total nitrogen, carbon and phosphorus digestibility was estimated in a wide size range of gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax) fed a commercially available conventional diet and an organic feed, as a previous step to assessing particulate waste output. Neither fish size nor feed nutrient content was seen to influence nutrient digestibility in either species. The organic diet provided higher carbon but lower nitrogen and phosphorus digestibility than conventional feed in both species. Simulations under real ongrowing conditions resulted in lower values for nitrogen and higher values for carbon particulate wastes when conventional feed was supplied to both species. Particulate phosphorus wastes were 2.6‐ to 3.4‐fold higher for fish fed the organic diet. Restrictions concerning NO the raw materials used for organic diet formulation and differences in nutrient bioavailability between the diets seemed to be the underlying reason for the differences found.     

Spatial and temporal variations of sediment quality in and around fish cage farms: A case study of aquaculture in the Seto Inland Sea, Japan

ABSTRACT: Fish cage farming generates large amounts of organic waste in the form of unconsumed feed and fecal matter, resulting in sediment deterioration and a threat to its own sustainability. Field studies analysed the scale of the impact of fish cage farming on sediment quality, variability of impact and spread of sediment enrichment in the vicinity of a fish farm. Two fish culture sites near the Fukuyama area of the Seto Inland Sea of Japan were chosen for the study. There was a significant difference between the quality of the sediment in aquaculture and non-aquaculture areas. The sediment underlying the fish cage farms was found to be extremely reducing, acidic and sulfidic. Sediment ignition loss did not vary markedly with the season. However, the redox potential and acid volatile sulfide content of aquaculture areas did show some seasonal variation. Sediment encircling a 165 m radius from the center of a farm in Yokota was judged as organically enriched by fish farming. A variation in sediment quality within the two sites and also within the stations was observed. Based on sediment quality, the stations could be categorized as less affected, highly affected or moderately affected.     

Using fatty acid markers to distinguish between effects of salmon (Salmo salar) and halibut (Hippoglossus hippoglossus) farming on mackerel (Scomber scombrus) and whiting (Merlangius merlangus)

Presence of coastal aquaculture activities in marine landscapes is growing with impacts on the wild fish that share these habitats. However, it is difficult to disentangle subsequent ecological interactions between these activities and marine fish communities. We evaluated the impact of both salmon and halibut farms on mackerel (Scomber scombrus) and whiting (Merlangius merlangus) sampled near sea cages using condition indices and fatty acid (FA) biomarkers. Results of the stomach content analysis indicated that mackerel and whiting consumed waste feed which was also reflected in their modified FA profiles. Both mackerel and whiting had elevated levels of FAs that are of vegetable oils origin. The use of vegetable oils as replacement for marine oils is a lot more common in salmon farming than halibut farming. Additionally, the overall effects of the two fish farms were more pronounced in whiting than in mackerel sampled near the sea cages. By allowing discrimination between sources of trophic interactions, this method could lead to more informed decisions in managing different farming activities.     

Salmon farming and the environment

Abstract. The growth of the aquaculture industry and the general awareness of the environment have increased the concern of' the environmental impact from aquaculture.
As fish farms are open systems, all material that is not harvested as fish is released to the environment. The most important effluents are solid particles like feed and faeces, dissolved substances like nutrients and excretion products, and antibacterial agents.
The effect of these substances varies with their nature and quantity and with local conditions. Production and biomass of phytoplankton seem to be little influenced. The benthic community beneath and close to the cages is often altered. At poorly flushed sites the sea-bed may be anoxic and methane and hydrogensulphide are released from the sediments. Wild fauna, like fish, otters and birds are attracted to the farms.
The respiration and excretion of the fish directly influence water quality. Usually the oxygen tension is somewhat reduced in the net cages, while the concentration of ammonia is elevated in the net. Such conditions are assumed to influence fish growth and health.
Most of the antibiotic agents used in fish farming are persistent and may remain in high concentrations in the sediments up to one year after medication. The frequency of resistant bacteria in the sea-bed is normally increased, and there is a temporary drop in sediment metabolism after medication. Wild fish have been found to have high residues of antibiotic agents.
The organic loading of the sea-bed, the evolution of resistant bacteria and residues in the wild flsh are considered to be the most severe environmental impact of aquaculture. These are all associated with effluent of large particles, and thus mainly restricted to the site area.     

海水工厂化养殖水处理系统的装备技术研究

工厂化养鱼(尤其是全封闭高密度养殖方式)是依靠工艺和设施装备技术的支撑，运用生态学原理及环境条件控制手段进行科学养殖。本文围绕海水工厂化养殖系统主要工艺环节(去除固体废弃物和水溶性有害物质、消毒、增氧、调温、水质测控)中涉及的装备技术和应用进行讨论。     

Diet of demersal fish species in relation to aquaculture development in Scottish sea lochs

The diets of demersal fish, principally haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus) and several flatfish species, sampled from four Scottish sea lochs (Hourn, Kishorn, Duich and Nevis) which support aquaculture sites, were examined in order to determine whether the impact of aquaculture on benthic biodiversity would affect the diets of demersal fish. Loch Kishorn had the highest maximum planned aquaculture production, loch Nevis follows and lochs Hourn and Duich have the lowest planned production. Samples were collected from locations less than and more than 2000 m from fish farm cages. Fish close to the fish farm cages were on average of greater individual weight than those further away from fish farms. Haddock ate predominantly Malacostracan crustacea, Ophiurid echinoderms and Polychaete annelids; whiting ate predominantly Malacostracan crustacea and teleost fish and flatfish ate Malacostracan crustacea, Polychaete annelids and Ophiurid echinoderms. A small number of saithe sampled had eaten mainly fish farm pellets. Dietary variation in each species was analysed in relation to loch, proximity to aquaculture facilities and fish size. Diet of whiting varied with body size. Dietary differences were observed between the lochs and between sites close to and far from farms in two lochs although these differences cannot be specifically attributed to aquaculture development. Controlling for differences between individual lochs, proximity to aquaculture facilities did not consistently affect diet composition.     

A contingent valuation of the biomitigation benefits of integrated multi-trophic aquaculture in Canada

Integrated multi-trophic aquaculture (IMTA) is the farming, in proximity, of aquaculture species from different trophic levels and with complementary ecosystem functions. IMTA allows one species’ uneaten feed and wastes, nutrients, and by-products to be recaptured and converted into fertilizer, feed, and energy for the other crops. By taking advantage of synergistic interactions between species, IMTA can help aquaculture evolve towards more responsible and sustainable systems. This study uses data from a contingent valuation survey to provide an estimation of the non-use benefits that, in the form of biomitigation of the external costs imposed on the marine environment, would be derived by Canadians from the adoption of IMTA for Atlantic salmon aquaculture. We find the benefits accruing to households who do not purchase salmon habitually would range between about $43 million/year and about $65 million/year for the next five years, depending on the treatment of ‘don’t know’ responses to the payment question.     

Preliminary Assessment of Biofouling on Offshore Mussel Farms

Biofouling is a significant operational problem for the aquaculture industry globally; however, options for on‐farm management are limited. In New Zealand, the green‐lipped mussel, Perna canaliculus, has historically been cultivated at inshore locations, but increased competition for space has led the industry to develop offshore farming sites several kilometers from the coast. We hypothesize that the distance to these farm sites from coastal locations, and their placement over extensive soft‐sediment habitats, may provide a barrier to colonization by biofouling species with limited natural dispersal abilities. A study of two offshore mussel farms revealed that they supported relatively impoverished biofouling communities by comparison with inshore mussel farms and other artificial structures. Offshore sites had a relatively low number of taxa and a low prevalence of short‐dispersing organisms such as ascidians, which are a problematic group of fouling organisms in aquaculture. We suggest that newly established offshore marine farms have the potential to be kept free of a range of problematic fouling organisms, provided the introduction of such species via human transport pathways can be mitigated.     

Impact of farming intensity and water management on nitrogen dynamics in intensive pond culture: a mathematical model applied to Thai commercial shrimp farms

A mathematical model is used to investigate the impact of farming intensity and water management on nitrogen dynamics in the water column of intensive aquaculture ponds. The model describes the input of ammonia, its assimilation by phytoplankton or nitrification, and the loss of nitrogen through sedimentation, volatilization, and discharge. The model is calibrated for two commercial shrimp (Penaeus monodon Fabricius) farms in Thailand. Assimilation by phytoplankton with subsequent sedimentation or discharge is the principal process of ammonia removal. When inputs of ammonia exceed the algal assimilation capacity (carrying capacity), nitrification and volatilization of excess ammonia become significant. Carrying capacity is negatively affected by non-chlorophyll turbidity, and was estimated as 6 t ha^?1 cycle^?1 at a non-chlorophyll extinction of 2.6 m^?1. In ponds managed within their carrying capacity, ammonia concentrations are lowest at no water exchange, reach a maximum at exchange rates between 0.2 and 0.4 day^?1, and decline again at higher rates. When the carrying capacity is exceeded, excess ammonia concentrations decline continuously with increasing water exchange. Average exchange rates used in intensive shrimp farms (up to 0.2 day^?1) reduce phytoplankton abundance and sedimentation within ponds, but not ammonia concentrations. Discharges are high in particulate nitrogen at water exchange rates up to 0.3 day^?1, but contain mainly dissolved nitrogen at higher rates.     

以大口黑鲈和大黄鱼配合饲料应用为例谈 改变鱼类营养和饲料研究范式

鱼类营养和饲料研究始于70年前并借鉴陆生动物营养研究经验形成了研究范式。在过去70年中,鱼类营养和饲料研究取得了大量的成果,这些研究成果推动了水产配合饲料技术的进步,为水产饲料产业从无到有、从小到大做出了贡献。然而,随着全球水产养殖规模的不断扩大,水产养殖发展面临的资源和环境压力日益增加,对水产饲料也提出了更高的要求。事实表明,根据一些鱼类营养和饲料研究成果所配方的饲料在养殖生产实践中往往不能取得预期的应用效果,这意味着在已有范式下取得的研究成果有时难以很好地满足现代鱼类养殖产业的需要。本文叙述了具有重要经济价值的两种肉食性鱼类大口黑鲈和大黄鱼配合饲料研发与应用的历程,指出对饲料蛋白需求的低估是限制配合饲料长期未能在大口黑鲈和大黄鱼养殖生产中应用的主要原因。早期研究报道大口黑鲈的饲料蛋白需求为400-440 g/kg,大黄鱼的饲料蛋白需求为450-470 g/kg。经过重新评估后将大口黑鲈和大黄鱼的最适饲料蛋白水平分别提高到480-510 g/kg和490-520 g/kg。在适宜的饲料蛋白水平下,投喂配合饲料的大口黑鲈和大黄鱼生长与投喂冰鲜鱼时相当。作者认为对饲料蛋白需求的低估与已有鱼类营养和饲料研究范式存在的不足有关,其表现为：（1）强调食物对鱼类生长的作用,但忽视了实验鱼遗传背景和食物以外的环境条件对生长和摄食的影响;（2）强调鱼类个体生长对评价营养需求和饲料质量的重要性,但忽视了鱼类个体生长差异并不能完全反映养殖产量和效益的事实;（3）强调生长和饲料利用效率作为鱼类营养和饲料研究评价指标的重要性,但忽视了养殖对环境和自然资源的负面影响是限制水产养殖产业可持续发展的瓶颈;（4）没有足够重视基础饲料配方在评价营养需求或饲料质量方面的影响,一些研究因基础饲料组成不当而产生没有实际意义的评价结果。针对上述问题,作者建议从概念、理论和研究方法方面对已有的范式做如下修改：（1）重视鱼类遗传背景和食物以外的环境条件对鱼类生长的影响,明确鱼类营养需求取决于其生长需求;（2）重视食物中各种营养素之间的相互作用,明确不同饲料原料在实现配方的营养平衡方面发挥着不同的作用;（3）重视对实验鱼种质和种群结构的选择,重视对照组和处理组个体生长差异的幅度对判断饲料处理效应的指示作用,重视饲料配方对渔业资源和环境等水产养殖可持续发展相关的内容的影响。经过修改后的研究范式更符合养殖生产实际,在此基础上开展研究所获得的成果也能够更好地指导配合饲料生产,为鱼类养殖产业的可持续发展提供更好的科技支撑。     

Impact of polychaete infauna on enzymatic protein degradation in marine sediments affected by intensive milkfish farming

Marine sediments at intensive fish farming sites in Bolinao‐Anda, northwestern Philippines, are characterized by strong oxygen depletion and the widespread predominance of sulphidic conditions precluding macrobenthic infauna. In less affected areas, however, small macrobenthos (Spionide polychaetes) was present. Experimental sediment mesocosms containing burrowing polychaetes were set up to investigate the possible links between macrofaunal bioturbation of the sediment and its proteolytic capacity to recycle protein‐rich fish farming waste. Relative to polychaete‐free sediment, the addition of small Spionide polychaetes had no significant effect on the proteolytic capacity but caused an increase in the redox potential. On the other hand, the addition of large Eunicide polychaetes caused an increase in both the proteolytic capacity and the redox potential. The deposition of commercial fish feed particles increased the proteolytic activities but decreased the redox potential particularly at a higher deposition rate (250 g m^?2 day^?1). Accumulation of hydrogen sulphide increased at deposition rates above 83 g m^?2 day^?1 and limited the survival of large polychaetes.     

Feed technology and production performance of Thai koi (Anabas testudeneus) in Bangladesh

ABSTRACT

Thai koi farming is relatively new in the aquaculture industry of Bangladesh. Costly industrial feed pellets is the main factor influencing the productivity of Thai koi (Anabas testudineus). Two types of feed, namely, floating and sinking, are commercially available in the country. The ingredients of both types of feed are more or less the same. Floating feed requires high technology, high pressure and temperature and hence is more expensive than sinking feed. Most of the Thai koi farmers use either floating or sinking feed, while some farmers use a mix of both types of feed. This article investigated the effects of these three feed types on Thai koi productivity using primary data collected from the Mymensingh district of Bangladesh. The performance of different feed types on productivity was investigated using the Cobb-Douglas production function and propensity score matching (PSM) methods. Floating feed led to the highest daily mean weight gain of fish, feed conversion ratios, and net returns. The regression and PSM results revealed that farmers using floating feed produced significantly higher quantity of fish per unit compared to those using the other feed types. The cost of feed per hectare was higher in the farms using the floating feed, but these farms earned extra return from the additional investment, compared with the farms that use the other feed types. Thai koi farmers are advised to use floating feed to reap higher production and returns on investment.     

Economics of fish farming in Saudi Arabia: Analysis of costs of tilapia production

Abstract

Because Saudi Arabia is a substantial importer of fish and its capture fishery is operating beyond maximum sustainable limits, it has a special interest in developing fish farming. It has been encouraging tilapia production. This study examines the costs of tilapia farming in the Central Region of Saudi Arabia using cross sectional data from 23 intensive fish farms. It provides information about the relative importance of different cost items such as variable costs and feed costs in total costs. Also, cost functions are estimated by ordinary least squares and a cubic cost function is found to provide the best fit to the available data. Minimum average cost of production occurs for 201 tonnes of tilapia per year per farm and profit is maximised for a production of 300 tonnes annually per farm. All farms operate at less than profit‐maximising scale and most operate at less than minimum efficient scale. The reasons could be low quality fry, low levels of management expertise in culturing tilapia and the secondary nature of tilapia farming. Lack of water is likely to limit future expansion of tilapia farming in Saudi Arabia.     

Economic Analysis of Alternative Snakehead Channa striata Feed

The use of low-value small-sized fish (LVSSF) both as aquaculture feedstuff for snakehead and for human consumption in Vietnam and Cambodia could result in demand outstripping supply as human population and aquaculture production grow. Replacing LVSSF for snakehead aquaculture with pelleted feed would reduce the pressure on stocks of LVSSF. This study addresses the economics of this replacement strategy for snakehead culture in Vietnam. Economic engineering methods were used to assess the effects of pelleted feed for low, medium and high-productivity scenarios. The study compared net present values (NPV), internal rates of return (IRR) and differences in NPV between farms using pelleted feed and those using LVSSF. It also included sensitivity analyses that related NPV and IRR to increased snakehead prices. Results demonstrated strong economic incentives for high-productivity farms to use pelleted feed. However, pelleted feed was too expensive for medium- and low-productivity farms. NPVs were more sensitive to reductions in the cost of pelleted feed than to increases in the cost of LVSSF or the cost of capital.     

海水鱼养殖碳、氮、磷排放及对环境影响的初步评价 ——以大西洋鲑养殖为例

依据排放成因,初步建立了海水鱼养殖中二氧化碳排放负荷和排放强度的测算方法；依据竹内俊郎法并综合考虑生物滤池处理效率,初步建立了海水鱼养殖的氮、磷排放负荷和排放强度以及排放总量的测算方法；依据海上生活污水排放标准,初步建立了氮、磷瞬时排放浓度的测算方法；利用浓度限值法测算了黄海冷水团区域氮、磷的环境容量。以大西洋鲑养殖数据为基础,测算了6种养殖模式的碳、氮、磷排放负荷和排放强度,并将测算的氮、磷年排放量、瞬时排放浓度的结果与黄海冷水团区域的环境容量进行比较分析,初步评估了养殖活动对环境的影响。结果显示,网箱养殖模式的二氧化碳排放负荷和排放强度均显著低于其他模式,循环水养殖模式的氮排放负荷和排放强度均显著低于全流水养殖模式,而6种养殖模式之间,磷排放负荷和排放强度的差异不显著,磷排放是制约扩大养殖规模的主要因素。     

Geochemical changes in white seabream (Diplodus sargus) earth ponds during a production cycle

The knowledge of geochemical processes in fishponds is important in defining farming strategies and the carrying capacity of these systems, and is therefore essential for the management and sustainability of semi‐intensive aquaculture in earth ponds. The main purpose of the present work, developed in the Aquaculture Research Station located in Ria Formosa, was to study the geochemical changes in semi‐intensive earth ponds of white seabream Diplodus sargus L. during a production cycle, and relate it to farming conditions (fish biomass and feeding rate). Settled material and sediment samples were collected in a fish production pond and in a non‐fish production pond during 2 years. The results obtained showed that particle‐settling rates (S, g m⁻² day⁻¹) increased linearly with time (t, days): S=0.7t–34, in the fishpond. Increasing deposition of particulate material increased the organic matter content of bottom sediments, particularly during the second production year. Organic matter mineralization, during periods of high temperatures, led to high nutrient concentrations in porewater (NH₄⁺, 965 μM; NO₃⁻, 40 μM; HPO₄²⁻, 39 μM) and subsequently to an increase in benthic primary production in the fishpond. The geochemical similarities between fishpond sediments and shallow coastal system's sediments, along with the high fish survival rate (94%), suggest that for the assayed farming conditions there were no environmental constraints within the pond. However, some impact on bottom sediments, namely, an increase in settled material, organic matter deposition, nutrients in porewater and microphytobentos production, was evident above a fish biomass of 500 g m⁻³ and a feeding rate of 150 kg month⁻¹, indicating that pond environmental conditions should be carefully monitored from this point on.     

Technical efficiency of carp production in Nepal: An application of stochastic frontier production function approach*

Abstract

Modern aquaculture is a relatively new activity among Nepalese farmers and a small contributor to the economy. Given the abundance of water resources and fish species, rising demand for fish, and its high profitability, aquaculture has potential for future expansion if it is given appropriate attention from the government. In Nepal, productivity in aquaculture is much lower compared to other countries in the region, which suggests that there is potential for increased fish production through technological progress and improvement in farm‐level technical efficiency. However, no formal analysis has yet been conducted to assess the productive performance of Nepalese aquaculture and its potential for future improvement. Against this background, this paper examines the technical efficiency and its determinants for a sample of fish pond farms from the Tarai region of the country using a stochastic production frontier involving a model for technical inefficiency effects. The estimated mean technical efficiency is 77%, with intensive farms being more efficient than extensive farms. The adoption of regular fish, water, and feed management activities has a strong positive effect on technical efficiency.     

胶州湾菲律宾蛤仔生态容量评估及其碳汇功能

胶州湾是我国重要的菲律宾蛤仔(Ruditapes philippinarum)养殖基地,为探究湾内菲律宾蛤仔的生态容量及其碳汇功能,本研究采用Ecopath模型法评估了胶州湾菲律宾蛤仔的生态容量,并利用Ecosim模块动态分析了菲律宾蛤仔生物量扩大对胶州湾生态系统结构与功能特征的潜在影响,同时估算了胶州湾菲律宾蛤仔个体及种群水平的碳收支情况。结果显示,胶州湾菲律宾蛤仔的生态容量为239.9 t/km2,虽然整体水平尚未达到生态容量,但局部养殖区域已远超出了菲律宾蛤仔的生态容量;当胶州湾菲律宾蛤仔生物量从当前增加至生态容量时,生态系统总流量、容量、优势度和循环指数分别提高了16.0%、3.9%、47.1%和103.0%,而熵值降低了10.4%,表明此时生态系统具有更高的成熟度与稳定性,但菲律宾蛤仔生物量扩大至生态容量10倍时会对生态系统产生不利影响甚至崩溃;菲律宾蛤仔个体在1个养殖周期内约摄取3 310.1 mg C,其中约46.2%的碳沉降至海底,约13.2%的碳通过收获移出,如按菲律宾蛤仔生物量达到生态容量时计算,胶州湾每年将有1.5万t碳以生物沉积形式沉降至海底,有0.6万t碳以收获形式移出。研究结果为指导菲律宾蛤仔增养殖产业的健康可持续发展、阐明菲律宾蛤仔的碳汇功能提供了理论依据与数据支撑     

Use of macrobenthic infaunal communities in the monitoring and control of the impact of marine cage fish farming

Benthic macrofaunal community changes are used extensively to monitor the impact of polluting discharges to the marine environment. Regulatory and pollution control authorities have recognized the particular value of the well studied and reported responses of infaunal communities to organic pollution including wastes from aquaculture. Benthic systems are embraced in both the consent (licence) to discharge and monitoring procedures for marine cage fish farms in the Clyde River Purification Board's (CRPB) area. The relevant protocols of the CRPB are described and data are presented from impact studies throughout west central Scotland, focussing on the sedimentary environment (macrobenthos, organic carbon and redox: Eh). Macrobenthic infaunal responses, though not fully understood, were considered to provide the best measure to date of determining the impacts of organic wastes from cage fish farming and a possible way forward in developing benthic Environmental Quality Standards (EQSs) for aquaculture. Some patterns in physico-chemical data were identified, but frequently, the relationship both with benthic infaunal data and each other were inconsistent. Grossly impacted faunal communities varied little between sites and could readily be described by the simple community determinands of abundance (A), species richness (S) and Shannon Weiner diversity index (H). Moderate to lightly impacted zones were less easily defined but detailed faunal studies have allowed the selection of some widely distributed marker species. However, site-specific observations emphasized the site individuality and difficulties of setting EQSs across the industry. Using the principles of enhanced species populations and by identifying marker species, measurable impacts were found to extend further than previously reported. In naturally enriched systems, like the Firth of Clyde and some sea lochs, difficulty in separating slight effects from background was experienced. Continued monitoring and impact assessment, as well as building a better biological data base, may help develop appropriate benthic EQSs relating to aquaculture.     

SUBSTITUTABILITY OF FISHMEAL AND FISH OIL IN DIETS FOR SALMON AND TROUT: A META-ANALYSIS

Intensive aquaculture, especially the production of carnivorous species requires artificial feeding. Marine proteins are preferred to vegetable proteins, since fishmeal and oil provide the essential nutrients required by farmed fish. Given the stagnant production of industrial species and the rapid increase in aquaculture production, fishmeal availability would pose a biological constraint on aquaculture contribution to world fish supplies in the future, unless alternative feed sources can be incorporated in diets. In this paper, the technical substitutability between fish and vegetable-based feeds for salmon and trout are assessed through the estimation of Morishima elasticities of substitution. These are derived from a meta-analysis production function based on a large number of published feed trials. The results suggest that vegetable oil may be a potential substitute for fish oil, particularly in salmon aquaculture, but fishmeal is likely to remain a necessary component of feed unless some new feed source can be developed.