Nutrient dynamics in integrated aquaculture–hydroponics systems

Changes in concentrations of dissolved Ca, Cu, Fe, K, Mg, Mn, NO₃-N, Na, P, and Zn, as a function of increasing biomass of Nile tilapia (Oreochromis niloticus) fed a commercial diet in integrated aquaculture–hydroponic systems growing romaine lettuce (Lactuca sativa longifolia cv. Jericho), were monitored over three, 28-day experimental trials. The integrated systems, 320–330 l in volume, were filled initially with a complete nutrient hydroponic solution, and were operated at a 100% recirculation rate. Treatment levels were 0 (control) 151, 377, 902, and 1804 g of fish/system and treatments were conducted in duplicate. Nutrient concentrations and mutual ratios of nutrients quickly departed from initial conditions because the relative proportion of dissolved nutrients excreted by fish and subsequently absorbed by plants differed. The removal of nutrients by lettuce, fish, and solids collection was determined as a function of treatment size. The objective of this study was to quantify both the flow of nutrients through representative integrated aquaculture–hydroponics systems and the effects of different quantities of feed nutrient input on changes in nutrient-specific concentrations.     

Dissolved nutrient release from solid wastes of southern bluefin tuna (Thunnus maccoyii, Castelnau) aquaculture

Finfish pens are point sources of dissolved nutrients released from fish metabolism or degradation of solid wastes. Nutrients leaching from uneaten feed and faeces are not usually quantified in mass budgets for these systems, leading to an overestimation of fish retention or deposition to the seabed. In this study, we investigated nutrient leaching from pellets and baitfish feed as well as faeces of southern bluefin tuna (Thunnus maccoyii) into seawater. Faeces were nitrogen depleted (51–54 mg N g⁻¹ dw) and phosphorus enriched (62–72 mg P g⁻¹ dw) compared with feeds (83–111 mg N g⁻¹ dw and 17–21 mg P g⁻¹ dw). Less phosphorus was available for leaching from pellets and faeces of pellet‐fed tuna (5–6%) than from baitfish and faeces of baitfish‐fed tuna (17–21%). The proportion of soluble nitrogen in pellets (15%) was also lower than in baitfish and faeces (35–43%). Leaching loads for a feed conversion ratio of 5 were estimated as 22 and 26 kg N tonne⁻¹ growth when baitfish or pellets were used as feed respectively. Phosphorus loads were estimated as 15 and 4 kg P tonne⁻¹ growth respectively. More than 90% of nitrogen loads, and approximately 50% of phosphorus, are likely to be released into seawater before solid wastes reach the seafloor.     

Water and nutrient budgets of ponds in integrated agriculture–aquaculture systems in the Mekong Delta, Vietnam

A participatory on-farm study analysed water and nutrient budgets of six low and four high water-exchange ponds of integrated agriculture–aquaculture (IAA) farms in the Mekong delta. Water, nitrogen (N), organic carbon (OC) and phosphorus (P) flows through the ponds were monitored, and data on fish production and nutrient accumulation in sediments were collected during a fish culture cycle. Results showed that, on average, only 5–6% of total N, OC or P inputs introduced into ponds were recovered in the harvested fish. About 29% N, 81% OC and 51% P accumulated in the sediments. The remaining fractions were lost through pond water discharges into adjacent canals. Fish yields and nutrient accumulation rates in the sediments increased with increasing food inputs applied to the pond at the cost of increased nutrient discharges. High water-exchange ponds received two to three times more on-farm nutrients (N, OC and P) while requiring nine times more water and discharging 10–14 times more nutrients than the low water-exchange ponds. Water and nutrient flows between the pond and the other IAA-farm components need to be considered when optimizing productivity and profitability from IAA systems.     

The Impact of Nutrient Concentration (N:P) and Manure Type on Fish Polyculture

Abstract

Nutrient availability is considered to have a major role in controlling primary productivity. Therefore, an important aspect of successful aquaculture management in fish culture systems is making available basic nutrients, for example, phosphorous (P), nitrogen (N), and carbon (C) in optimal concentrations. The use of fertilizers in relation to pond productivity has been studied in order to develop better fertilization procedures under given environmental conditions. Many researchers from across the world have suggested different N:P ratios for optimizing fish production. The primary aim of this study was to understand the influence of nutrient quality and quantity on fish and primary productivity in terms of optimizing fish production. Two objectives of this study include evaluating the performance of pig and cow manures in terms of primary productivity and fish production; and understanding the influence of different N concentrations ranging from 1-2 ppm on fish production while P was maintained at 0.5 ppm. It was evident from this research that fish species nutrient-sensitivity to nitrogen concentrations ranging from 1-2 ppm was significantly different. The 1 ppm N:0.5 ppm P concentration was found to be the most suitable nutrient ratio for pond fertilization as significantly higher fish production and lower mortality were recorded in this treatment. In terms of plankton and fish production, pig manure was found to be significantly more effective than cow manure. Higher nutrient (>1 ppm N) concentrations negatively impacted zoo-plankton and zoo benthos development. Daily manure application would considerably reduce the organic load in the fish culture system, enabling more efficient use of nutrients for primary and secondary production.     

Bio-filters: The need for an new comprehensive approach

The aquaculture industry struggles to profit in light of low product prices, increasing costs of inputs and constrains due to environmental, water and land limitations.

Intensive aquaculture systems are relevant to efficiently produce fish and shrimp. The two important limiting factors of intensive aquaculture systems are water quality and economy. An intrinsic problem of these systems is the rapid accumulation of feed residues, organic matter and toxic inorganic nitrogen species. This cannot be avoided, since fish assimilate only 20–30% of feed nutrients. The rest is excreted and typically accumulates in the water. Often, the culture water is recycled through a series of special devices (mostly biofilters of different types), investing energy and maintenance to degrade the residues. The result is that adding to the expenses of purchasing feed, significant additional expenses are devoted to degrade and remove 2/3 of it.

There is a vital need to change this vicious cycle. One example of an alternative approach is active suspension ponds (ASP), where the water treatment is based upon developing and controlling heterotrophic bacteria within the culture component. Feed nutrients are recycled, doubling the utilization of protein and raising feed utilization. Other alternatives, mostly based upon the operation of a water treatment/feed recycling component within the culture unit are discussed.

The present paper was presented in the biofilter workshop held in Honolulu, 8–11 November 2004. The main purpose of this paper was to raise new ideas and new options toward the planning and operation of intensive fish/shrimp ponds.     

Effects of dietary phosphorus and lipid levels on utilization and excretion of phosphorus and nitrogen by rainbow trout (Oncorhynchus mykiss). 2. Production-scale study

In a 8-week production-scale experiment at a commercial trout farm, the effects of dietary lipid level and phosphorus level on phosphorus (P) and nitrogen (N) utilization of rainbow trout (initial mean weight 99 g) were assessed. A low-phosphorus, high-lipid experimental diet (457 g protein, 315 g lipid, 9.1 g P  kg^–1 dry diet) was compared with a commonly used commercial diet (484 g protein, 173 g lipid, 13.6 g P  kg^–1 dry diet). P and N budgets were constructed using data from the production-scale experiment and digestibility data for the two diets. In addition, orthophosphate and ammonia-N waste were measured in effluent over one 24-h period. Relative to the commercial diet, the experimental diet resulted in significantly increased feed efficiency ratio, N retention and P retention, and substantially reduced dissolved, solid and total P waste (g kg^–1 dry feed). Although N retention resulting from the experimental diet was higher, this was attributable to higher N (protein) digestibility of the experimental diet. Solid N waste (g kg^–1 dry feed) resulting from the experimental diet was substantially lower, but dissolved N waste (g kg^–1 dry feed) was not significantly different relative to the commercial diet. Mean effluent orthophosphate production (mg day^–1 kg^–1 fish) of fish fed the experimental diet was substantially lower than that of fish fed the commercial diet ( P  < 0.05), but effluent ammonia-N production (mg day^–1 kg^–1 fish) was not significantly affected by dietary treatment.     

Ration level for salmonids: I. Growth, survival, body composition, and feed conversion in Atlantic salmon fry and fingerlings

Twelve groups of Atlantic salmon (Salmo salar L.), raised in fibre-glass tanks, were fed at 12 ration levels for 7 periods, each period lasting 28 days. The basic ration level was calculated from an expected maximum growth rate, depending on fish size and water temperature. This level was defined as “level 1.00”. The experimental ration levels varied from 0.50 to 3.25 in intervals of 0.25.

During the start-feeding period there was an average survival rate of 95%. After the remaining 6 periods the group which was fed least had a survival rate of 48%. The other groups had an average survival rate of 81%. In all 7 periods, increasing the ration levels from 0.50 to 1.00 resulted in increased growth. A further increase in ration level did not result in extra growth. The weight distribution of the fingerlings was bimodal, with the majority of fish in the scantiest fed groups being in the lower mode. The majority of the fish in the adequately fed groups were distributed in the upper mode.

The water temperature varied from 10 to 17°C, and the thermal sum was 2430 day-degrees. The average final weight of the fish which received ration levels from 1.00 to 3.25 was 28.3 g, while the fish on the scantiest ration weighed only 9.6 g at the end of the study. The feed conversion rate, which was 0.9–1.0 kg dry feed/kg growth for the two underfed groups, ranged from 1.0 to 3.0 in the other groups. The chemical composition of the fish varied according to fish size and ration level.     

Photoperiod influences the growth, food intake, feed efficiency and digestibility of red sea bream (Pagrus major)

Two consecutive trials were conducted to investigate the effects of photoperiod manipulation on growth rate, food intake and feed conversion efficiency (Trial 1), and the digestibility of nutrients and energy (Trial 2) in red sea bream, Pagrus major (body weight 19–120 g). Fish were exposed to four photoperiods (6L:6D, 12L:12D, 16L:8D and 24L:0D) with light intensity 1500 lx on the water surface. The fish were fed with a commercial diet to apparent satiation. In Trial 2, 0.5% chromic oxide (Cr₂O₃) was used as an inert marker. Significantly higher weight gain and specific growth rates were observed in fish exposed to a 24L:0D photoperiod followed by 16L:8D, 6L:6D and 12L:12D photoperiods (P < 0.05). Food intake and feed conversion efficiency (FCE) were also significantly higher in fish exposed to 24L:0D followed by 16L:8D, 6L:6D and 12L:12D photoperiods (P < 0.05). Fish exposed to 24L:0D and 16L:8D photoperiods showed significantly higher lipid and energy digestibility than those exposed to a 12L:12D photoperiod (P < 0.05). The results demonstrated that the enhancement of growth performances under 16L:8D and 24L:0D photoperiods were attributed to improved appetite, greater food intake and higher feed conversion efficiency as well as higher digestibility.     

Autumn conditioning of the oyster Crassostrea gigas: a new approach

Gametogenesis, emitted gametes and larval yield (D larvae) of the oyster, Crassostrea gigas (Thunberg), were simultaneously examined in laboratory under two different conditions of temperature and photoperiod. One batch (“natural” cycle, NC) followed the equivalent cycle of average conditions of these parameters measured in La Tremblade (Charente-Maritime, France) during the last 15 years. The second batch (“accelerated” cycle, AC) was maintained under a variation two times faster of these parameters. Three conditioning experiences were performed during October, November and December 1998 with oysters from both NC and AC conditions. “Accelerated individuals” produced oocytes in growing stage from October and mature oocytes were noticed from December. In contrast, oysters from NC produced growing oocytes until January. Animals in AC produced 42% (October), 56% (November) and 96% (December) of mature oocytes after conditioning. Only the “natural” lot conditioned in December showed growing (23%) and mature oocytes (8%). Higher Walne–Mann index (WMI) values were recorded for “accelerated oysters” and significant differences (P<0.05) between treatments were noticed during October and November, suggesting nutrient accumulation before conditioning in the “accelerated” condition. Gamete emission and D larval yield results were equivalent to those reported in literature during early spring for the same species. The effect of temperature and photoperiod is discussed in order to understand their relationship with gametogenesis under these particular experimental conditions. It was demonstrated that internal clocks regulating gametogenesis can be change if stimulating factors (environmental cues) also change.     

Coldwater RAS in an Arctic charr farm in Northern Norway

Use of coldwater recirculating aquaculture systems (RAS) are still very rare in Norway, and only two farms are producing Arctic charr. This project took place in one of these commercial Arctic charr farms; Villmarksfisk AS in Bardu, Northern Norway.The farm gets its make-up water from ground water that holds 5 °C year around. Temperature in the rearing water varies between 7.5 °C (“low”) to 12 °C (“high”) through the year. The biological filter in the RAS seems to work stable at both “low” and “high” temperatures, including after incidents when feeding has been stopped for a day and started on top again the day after. Such an extreme change in loading was measured as a 70% increase in TAN concentration, with only minor changes in nitrite levels recorded. The biofilter also kept the nitrite stable and low in spite of diurnal variation in TAN excretion at normal feeding regimes (every day in three periods at day-time).The farming concept is to stock the farm with wild caught juvenile fish for on-growing to market size fish (0.75–1.00 kg). A drop in growth rate during early autumn has been a main concern for the farm. This may reflect a seasonal shift in growth potential, sometimes referred to as “autumn depression”. Interestingly, there is little sign of seasonal changes in the growth of hatchery-produced fish tested in the farm. Sampling of water quality through the seasons in tanks holding fish undergoing such growth depressions indicate that TAN excretion is much higher per kg feed used in the wintertime than in the springtime. This observation corresponds with the lack of weight gain during wintertime despite that the fish is feeding. Thus, feed conversion calculations indicate that feed utilization also varies with season reaching its nadir during this period.Both challenges concerning RAS in cold water and strongly reduced growth in autumn and winter time, have been investigated from 2005 to 2007 in a project financed by the Norwegian research council and the partners in the agricultural framework agreement.     

Comparison of nutrients release among some maricultured animals

Integrated mariculture is a feasible method to maintain sustainable and high productivity of aquaculture. The choice of cultured animals and biofilters in the integrated system has to be made on the basis of their nutrient release rates and the clearance rate of each component of the system. We are examining the nutrient release rates among fish (mangrove snapper, Lutjanus russeli, and sea perch, Abudefduf septemfasciatus), abalone (Haliotis diversicolor), scallops (Chlamys noblis), and green mussels (Perna viridis) in the laboratory. Fish feed is the major sources of inorganic nutrient input in fish farms. The orthophosphate and ammonia release rates of minced trash fish (1593 μg P g⁻¹ day⁻¹ and 150 μg N g⁻¹ day⁻¹) were respectively 6–12 times and 4–88 times higher than those of cultivated fish. Mangrove snapper had the overall highest nutrient release rate, followed by sea perch, abalone, scallops, and mussels for nitrite and nitrate; and followed by abalone, sea perch, mussels, and scallops for orthophosphate and ammonium. Among mollusks, abalone had the highest orthophosphate (162 μg P g⁻¹ day⁻¹), nitrate (1.4 μg N g⁻¹ day⁻¹), nitrite (1.6 μg N g⁻¹ day⁻¹) and ammonium (25.0 μg N g⁻¹ day⁻¹) release rates per gram wet weight per day. Abalone released large amounts of orthophosphate, nitrite and nitrate in the experiment. Scallops and green mussels had low nutrient release rates.     

Nutrient budgets in tanks with different stocking densities of hybrid tilapia

Nitrogen and phosphorus budgets were estimated in 12 indoor fiberglass tanks stocked with hybrid tilapia (Oreochromis niloticus×O. aureus) at densities of 1 kg, 5 kg, 10 kg and 15 kg/m³ and reared for 14 days. Each density was replicated three times, and the experiment was repeated five times. The water in each tank was changed daily. Fish were fed a 34% protein tilapia feed to satiation twice daily. Feed consumption rate significantly decreased (P<0.05) with increasing density, but the FCR did not vary significantly (P>0.05) among the treatments. The production of one kilogram of fish required 2.0–2.2 kg of feed in different stocking density treatments, while 87.1–95.6 g nitrogen and 12.6–13.8 g phosphorus were released into the water, as metabolic waste. Of the feed input, 21.4% of the nitrogen and 18.8% of the phosphorus were incorporated in the fish harvested.     

Reuse strategy of wastewater in prawn nursery by microbial remediation

A strategy of reusing the prawn nursery wastewater was developed by the previous remediation with Bacillus subtilis and nutrients addition. The suggested method was preliminarily verified in rearing prawn larval. Bacteria assimilation is proved as a main and powerful mechanism for removing dissolved organic matter (DOM) and total ammonia nitrogen (TAN) in the experiments. The process of microbial remediation could be featured as two sequential stages: DOM degradation and TAN reduction. In the first stage (from day 0 to day 2), DOM was degraded directly as the bacterial carbon and nitrogen sources. The 48-h COD removal efficiencies (R_COD) in the treatment were 57.7±5.5%, showing significantly different from 12.2±4.1% in control. In the second phase (from day 2 to day 5), the deficiencies of C and P source relative to N source might limit bacteria proliferation and TAN removal. The glucose and/or phosphate addition significantly influenced the TAN removal performance, while the addition of vitamin mixture and/or microelement solution was not. When the initial TAN level was nearly 5 mg N/l, the optimal TAN removal efficiencies from day 2 to day 5 were above 85% in the treatments with both glucose and phosphate additions, where the white microbial floccules were observed to suspend. The C/N or N/P weight ratio of 5.4:1or 5–7:1 was suggested for remediating the nursery effluents. The situation that the maximum bacterial levels did not exceed 10⁸ CFU/ml was estimated to correlate with the formation of microbial floccules. After 5 days of microbial remediation by these adequate methods, the wastewater had been became the “microbially matured” water suitable to reuse. In the practical operations, the nutrient supplements were directed by Glucose/TAN weight ratio of 13:1 and KH₂PO₄/TAN weight ratio of 0.6–0.9:1. The results of the application trial pointed out that the remediated water reclaimed to the larvae culture tanks did not produce observable deleterious effects on the water quality and on the mortality of the prawn larvae. The method of reusing the remediated wastewater by microbial agents and nutrients additions will be advantageous to reduce both production cost and environmental pollution in the inland hatchery and nursery for prawn.     

Phosphorus utilization in rainbow trout (Oncorhynchus mykiss) fed practical diets and its consequences on effluent phosphorus levels

Excessive dietary phosphorous (P) concentrations in effluents from aquaculture present a major environmental problem. We therefore studied the effect of dietary P and vitamin D₃ on P utilization by rainbow trout-fed practical diets and on P concentrations in the soluble, particulate and settleable components of the effluent from fish tanks. Rainbow trout (average weight: 78 g, initial biomass: 13 kg in 0.7 m³ tanks) were fed for 11 weeks, practical diets that varied in total P, available P, and vitamin D₃ concentrations. Soluble, particulate (10–200 μm) and settleable (>200 μm) P in the effluent were sampled every 0.5–6 h for 1–3 days in the third and eleventh weeks of the experiment. Trout in all diets more than doubled their weight after 11 weeks. Increasing the concentrations of available dietary P from 0.24% to 0.88% modestly enhanced growth rate. Feed conversion ratio (FCR) and biomass gain per gram P consumed decreased as dietary P concentrations increased. Carcass P, daily P gain, and plasma P concentrations were lower in fish fed with low P diets. Soluble P concentrations in the effluent peaked immediately after and again 4–6 h after feeding, and is a linear function of available dietary P. No soluble P would be produced during consumption of diets containing less than 0.22±0.02% available P. Above this dietary concentration, soluble P would be excreted at 6.9±0.4 mg/day/kg for each 0.1% increase in available dietary P. Particulate P concentrations in the effluent were independent of dietary P concentrations. Settleable, presumably fecal, P concentrations tended to increase with dietary P concentrations. In trout fed with low P (0.24% available P, 0.6% total P) diets, 60% of total dietary P were retained by the fish and the remaining 40% were excreted in the effluent as settleable P (20–30%) and particulate or soluble P (10–20%). In trout fed with high P (0.59–0.88% available P; 0.9–1.2% total P) diets, 30–55% of total dietary P was retained by fish, and the remaining 15–25% appeared in the effluent as settleable P, 20–55% as soluble P, and 5–10% as particulate P. Vitamin D₃ did not affect fish growth nor effluent P levels. Physicochemical management of aquaculture effluents should consider the effect of diets on partitioning of effluent P, the peaks of soluble P concentration following feeding, and the contributions of particulate P to total P in the effluent. Increasing our understanding of how dietary P is utilized and is subsequently partitioned in the effluent can contribute significantly towards alleviating this important environmental and industry problem.     

Inter-specific variation of the mitochondrial r16S gene among silversides, “Peces Blancos”, (Atherinopsidae: Menidiinae) and its utilization for species identification

Analysis of 570 nucleotide sequences of the mitochondrial r16S gene of four species of silversides “peces blancos” (Chirostoma sp.) and of two euryhaline related species Membras martinica and Menidia menidia indicated variation that aided in development of a DNA-based method for species identification. The nucleotide sequence data showed levels of inter-generic genetic variation that ranged from 3.3–7.9% and from 1.06 to 1.6% at the inter-specific level. The variation observed allowed the identification of 18 diagnostic restriction enzymes that in any combination of two or three could aid in the diagnosis of species of “peces blancos”; six of these enzymes could also discriminate between the genera Membras and Menidia; the enzymes AseI, CviAII and FatI discriminate the genus Membras from Chirostoma; and the combination of any of the enzymes BsaAI, CviAII, FatI or HpyCH4IV discriminate Menidia from the “peces blancos”. PCR-RFLP analysis of amplified mitochondrial r16S fragments of 90 un-identified “peces blancos” from Lake Patzcuaro utilizing the restriction enzymes HpyCH41V, TaqI, BsmF1 and BbvI allowed us to diagnose unambiguously cultivated Chirostoma estor and C. humboldtianum in juvenile and adult stages. The use of a non-invasive method to PCR-amplify specific DNA markers from live brood stocks suggests use of this tool for identification of endangered or threatened species.     

Off flavor characterization and origin in French trout farming

The results of a study on off-flavor problems in four French trout (Onchorynchus mykiss) farms are presented. Methodological aspects on sensory analyses and volatile compounds quantification in fish are discussed. Detection of odorous compounds by gas chromatography–mass spectrometry shows that significant concentrations of geosmin (up to 18 μg/kg in fat) are found in trout. The sensory evaluation, the presence/absence of geosmin in the flesh and the identification of off-flavor compounds producers demonstrate the implication of Microcoleus in the appearance of earthy/musty off-flavors. The presence of this particular cyanobacterium is linked to the deterioration of water quality during the water recirculation period. Correlations between chemical and sensory detection in the flesh indicate that the taste evaluation enables the differentiation of the four categories “non-tainted”, “slightly-tainted”, “tainted” and “strongly-tainted”. However, the average concentrations of geosmin found for these different intensities are relatively limited, from 0.2 to 4.9 μg/kg. Finally, recommendations are made to allow a more effective control of off-flavor occurrences.     

Ration level for salmonids II. Growth, feed intake, protein digestibility, body composition, and feed conversion in rainbow trout weighing 0.5–1.0 kg

Six groups of rainbow trout (Salmo gairdneri Richardson), raised in fibre-glass tanks, were fed at six different ration levels for two periods of 21 days each. Each tank contained 20 individually tagged fish with a mean initial weight of 415 g. The water temperature averaged 8.4°C and 10.2°C in the two periods. The basic ration level was calculated from an expected maximum growth rate, depending on fish size and water temperature. This level was defined as “level 1.000”. The other experimental levels were 0.125, 0.250, 0.500, 2.000, and 4.000 relative to this, respectively.

No fish died during the experiment. The growth of the fish increased significantly with increasing rations up to the level 2.000. The fish lost weight at the ration level 0.125. The growth rate was near zero at the ration level 0.250. The growth of the fish receiving the highest ration level was 1.72% of their weight per day. The variation in growth of the fish within various weight classes was influenced by the ration level so that the growth distribution of the scantiest fed groups was skewed to the left. There was no skewness in the distribution of the most plentifully fed groups. The ration level had no significant effect on the apparent protein digestibility. Measurements of the feed intake using a radioactive isotope in a 6-h meal showed that the fish ingested all the feed at the ration levels from 0.125 to 1.000. The feed intake recorded was equivalent to the requirements for fish growth at the ration level 2.000, while it was lower at the ration level 4.000. The liver weight percentage increased with increasing ration while the dressed-out carcass percentage decreased. The chemical compostion of the carcass was influenced to a greater extent by the feeding than that of the intestines. The feed conversion efficiency (FCE) and the productive protein value (PPV) of the feed were highest at the ration level 1.000. The values obtained were an FCE of 1.0 kg growth per kg dry feed ingredients and a PPV of 41%.     

Mass balanced based LCA of a common carp-lettuce aquaponics system

An aquaponics system (AS) is an integrated system that combines a recirculating aquaculture system and a hydroponics system (HS). It is designed to recover nutrients released from fish and transfer them to plants to provide a system more environmentally-friendly than the two systems working separately. As a result, several AS are under development, but little information is available about their overall performances. The aim of this study was to assess nutrient-use efficiency and environmental impacts of an AS, specifically a common carp-lettuce AS located in a greenhouse. Nutrient budgets of nitrogen (N) and phosphorus (P) were calculated and Life Cycle Assessment (LCA) was performed for the AS and for a lettuce Individual Hydroponics System (IHS), similar to the HS of the AS, operating in the greenhouse at the same time. The experiment was performed over a 52-day cycle, which corresponds to the growing time required to harvest marketable lettuce. The nutrient budgets were well balanced, with 24.6% of the N unaccounted-for, most likely due to N2 gas emission, and 6.6% of the P unaccounted-for, most likely due to having underestimated the quantity of sediment. At the beginning of the experiment, N represented 55.9%, 37.1% and 0.1% of the total N input in the formulated feed, stocked fish and lettuce seedlings, respectively. At the end of the experiment, N represented 47.6% and 0.4% of the total N input in the harvested fish and lettuce, respectively. At the beginning of the experiment, P represented 56.94%, 40.20% and 0.03% of the total P input in the formulated feed, stocked fish and lettuce seedlings, respectively. At the end of the experiment, P represented 51.52% and 0.42% of the total P input in the harvested fish and lettuce, respectively. LCA clearly indicated two environmental impact hotspots: the origin of nutrients and energy use. One kg of lettuce growth in the AS clearly had lower environmental impacts than that in the IHS for climate change, acidification, eutrophication, land competition and cumulative energy demand; however, a decrease in water dependence was not observed. The indicator for net primary production use highlighted the dependence of the AS on natural resources, especially fish meal and fish oil. Compared to the use of chemical nutrients in the IHS, the use of nutrients from formulated feed in the AS decreased climate change impact but increased the use of natural resources.     

Food inputs, water quality and nutrient accumulation in integrated pond systems: A multivariate approach

A participatory on-farm study was conducted to explore the effects of food input patterns on water quality and sediment nutrient accumulation in ponds, and to identify different types of integrated pond systems. Ten integrated agriculture-aquaculture (IAA) farms, in which ponds associate with fruit orchards, livestock and rice fields were monitored in the Mekong delta of Vietnam. Pond mass balances for nitrogen (N), organic carbon (OC) and phosphorus (P) were determined, and pond water quality and sediment nutrient accumulation were monitored. Data were analyzed using multivariate canonical correlation analysis, cluster analysis and discriminant analysis. The main variability in pond water quality and sediment nutrients was related with food inputs and water exchange rates. Water exchange rate, agro-ecological factors, pond physical properties and human waste input were major variables used to classify ponds. Classification was into: (1) low water exchange rate ponds in the fruit-dominated area, (2) low water exchange rate ponds in the rice-dominated area receiving homemade feed, and (3) high water exchange rate ponds in the rice-dominated areas receiving wastes. Pond water exchange rate was human-controlled and a function of food input patterns, which were determined by livelihood strategies of IAA-households. In the rice-dominated area with deep ponds, higher livestock and human wastes were found together with high water exchange rates. In these ponds, large organic matter loads reduced dissolved oxygen and increased total phosphorus concentrations in the water and increased nutrient (N, OC and P) accumulation in the sediments. In the rice-dominated area with wide ponds, higher homemade feed amounts were added to the ponds with low water exchange rate. This resulted in high phytoplankton biomass and high primary productivity. The contrary occurred in the fruit-dominated area, where fish were grown in shallow and narrow ponds, receiving more plant residue which resulted in lower phytoplankton biomass and lower sediment nutrient accumulation.