AI: Food Value, Water Use Efficiency and Economic Productivity of an Integrated Aquaculture-Olericulture System as Influenced by Component Ratio – AI

Food Value, Water Use Efficiency and Economic Productivity of an Integrated Aquaculture-Olericulture System as Influenced by Component Ratio

Enhancing Food Value, Water Use Efficiency, and Economic Productivity in Integrated Aquaculture-Olericulture Systems: The Impact of Component Ratios

M.R. McMurtry², D.C. Sanders³, R.G. Hodson⁴ and B.C. Haning^5,6

Department of Horticultural Science, UNC Sea Grant Program and Department of Plant Pathology, North Carolina State University, Raleigh, NC 27695

Additional index words: biofiltration, Cucumis sativus, hydroponics, integrated aquaculture, Lycopersicon esculentum, Oreochromis mossambicus, Oreochromis niloticus, sand culture.

Abstract.

Fish and vegetable production were linked in a recirculating water system. Hybrid tilapia (Oreochromis mossambicus (Peters) x O. niloticus (L.)) were grown in tanks and fed a commercial feed. Tomato (Lycopersicon esculentum Mill. ‘Laura’) was grown in summer 1988, cucumber (Cucumis sativus L. ‘Fidelio’) in fall 1988, and tomato ‘Kewalo’ in spring 1989 in a Raleigh NC greenhouse.

Four tank to biofilter volume ratios were studied. Plants were grown in the biofilters at 4 plants m^-2 and surface irrigated 8 times daily with water from the associated fish tank. Biofilter drainage returned to the fish tanks by gravity. Each system received identical nutrient inputs and plants received equal water. Biological filtration, aeration, and mineral assimilation by plants maintained water quality within limits suitable for tilapia.

Dissolved oxygen levels, make-up water, fish biomass increase and growth rates increased with biofilter volume. Total fruit yield increased but yield per plant decreased with increasing biofilter volume. Caloric content of the increase in fish biomass per liter of total water decreased while that of tomato increased with increasing biofilter volume. Calories per liter of water used in the combined yields did not differ by treatment. Total protein production per liter of water used decreased with increasing biofilter volume. Both caloric value and protein production in the combined outputs increased with biofilter volume irrespective of water consumption.

This study evaluates the food value, water use efficiency, and economic productivity of an integrated aquaculture-olericulture system, focusing on the impact of varying biofilter to tank volume ratios. Hybrid tilapia (Oreochromis mossambicus x O. niloticus) and various vegetable crops were cultivated in a recirculating water system. Results indicate that increasing biofilter volume enhances vegetable yield and nutrient assimilation but reduces fish biomass per unit of water. The findings suggest that optimizing biofilter volume can significantly improve the sustainability and economic viability of integrated aquaculture systems, particularly in arid regions.

Introduction

In arid and semi-arid regions, agriculture creates a heavy demand on water resources, and returns in terms of productivity are low (Kowal and Kassam, 1978). The integration of aquaculture with olericulture offers a promising solution to these challenges by conserving water resources and nutrients, achieving high levels of fish and vegetable production per unit area, and increasing food value and protein per unit volume of water (Rakocy, 1989b; McMurtry et al., 1990a, 1990b).

This study aims to evaluate the food value, water use efficiency, and economic productivity of an integrated aquaculture-olericulture system as influenced by the biofilter to tank volume ratio. The constraints of water supply, soil type, and land availability do not limit the use of recirculating systems as they do in pond or cage aquaculture systems (Rakocy, 1989a).

Integrated systems use less than 1% of the water required in pond culture for equivalent tilapia yields (Rakocy, 1989b; McMurtry et al., 1990a). Such symbiotic systems are applicable to the needs of arid or semi-arid regions where fish and fresh vegetables are in high demand (Rakocy, 1989b). The expansion of aquaculture should be given high priority in developing and developed countries (World Comm. on Environment and Development, 1987).

Dissolved and suspended organic materials accumulate rapidly in aquaculture systems and must be removed for efficient fish production (Nair et al., 1985). Previous integrated fish-vegetable systems have removed suspended solids from the water by sedimentation in clarifiers prior to plant application (Rakocy, 1989b). Removal of these solids resulted in insufficient residual nutrients for good plant growth. Acceptable fruit yields in integrated systems have only been achieved with substantial supplementation of plant nutrients (Lewis et al., 1978, 1981; Rakocy, 1989b).

Reciprocating biofilters, which are alternately flooded and drained, provide advantages of uniform distribution of nutrient-laden water in the filtration medium during the flood cycle and improved aeration from atmosphere exchange with each dewatering (Lewis et al., 1978; Paller and Lewis, 1982; Rakocy, 1989a). These advantages benefit both nitrifying bacteria and plant roots (Lewis et al., 1978; Paller and Lewis, 1982; Rakocy, 1989b).

Aqueous nitrate concentrations in recirculatory aquaculture have been adequately regulated when integrated with vegetable crops on a reciprocative flow basis (Lewis et al., 1978; Watten and Busch, 1984; Rakocy, 1989b; McMurtry et al., 1990e).

The primary objective of this study was to evaluate fish and vegetable yields per unit of water used and per unit nutrient input as influenced by the biofilter to tank (v/v) ratio. Efficiency of water utilization in food production (e.g., grams protein l-1 and kCal. l-1) was the fundamental impetus in developing this technique. A second objective was to project economic productivity per composite unit area as influenced by component ratio.

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In arid and semi-arid regions, agriculture creates a heavy demand on water resources, and returns in terms of productivity are low (Kowal and Kassam, 1978). “Production of fish from natural waters or by aquaculture is both feasible and highly desirable in arid zones.” (Welcome, 1977). Integrating aquaculture with olericulture includes the following benefits: 1) conservation of water resources and nutrients, 2) high levels of fish and vegetable production per unit area, and 3) increased food value and protein per unit volume of water (Rakocy, 1989b; McMurtry et al., 1990a, 1990b).

The constraints of water supply, soil type and land availability do not limit the use of recirculating systems as they do in pond or cage aquaculture systems (Rakocy, 1989a). Integrated systems use less than 1% of the water required in pond culture for equivalent tilapia yields (Rakocy, 1989b; McMurtry et al., 1990a). Such symbiotic systems are applicable to the needs of arid or semi-arid regions where fish and fresh vegetables are in high demand (Rakocy, 1989b). “The expansion of aquaculture should be given high priority in developing and developed countries!” (World Comm. on Environment and Development, 1987).

Recirculating aquacultural water has potential for hydroponic cultivation of higher plants (Naegal, 1977; Lewis et al., 1978; Watten and Busch, 1984; McMurtry et al., 1990b). Aquacultural water has been successfully used to grow many different vegetable species in biofilters operated on a reciprocative basis (McMurtry et al., 1990e). Dissolved and suspended organic materials accumulate rapidly in aquaculture systems and must be removed for efficient fish production (Nair, et al., 1985).

Previous integrated fish-vegetable systems have removed suspended solids from the water by sedimentation in clarifiers prior to plant application (Rakocy, 1989b). Removal of these solids resulted in insufficient residual nutrients for good plant growth. Acceptable fruit yields in integrated systems have only been achieved with substantial supplementation of plant nutrients (Lewis et al., 1978, 1981; Rakocy 1989b).

These advantages benefit both nitrifying bacteria and plant roots (Lewis et al., 1978; Paller and Lewis, 1982; Rakocy, 1989b). Aqueous nitrate concentrations in recirculatory aquaculture have been adequately regulated when integrated with vegetable crops on a reciprocative flow basis (Lewis et al., 1978; Watten and Busch, 1984; Rakocy, 1989b; McMurtry et al. 1990e).

The primary objective of this study was to evaluate fish and vegetable yields per unit of water used and per unit nutrient input as influenced by the biofilter to tank (v/v) ratio. Efficiency of water utilization in food production (e.g., grams protein I-1 and kCal. 1-1) was the fundamental impetus in developing this technique. A second objective was to project economic productivity per composite unit area as influenced by component ratio.

Materials and Methods

Olericulture was integrated with recirculatory aquaculture in a greenhouse in Raleigh, NC (McMurtry et al., 1990a, 1990b, 1990c). All-male (sex-reversed) hybrid tilapia (Oreochromis mossambicus (Peters) x O. niloticus (L.)) were cultivated in tanks which were physically associated with a biofilter utilizing builders’ grade sand as substrate (McMurtry et al., 1990a).

Four tank to biofilter volume (BFV) ratios were selected as treatments (McMurtry et al., 1990a). Fish were fed modified Purina Fish Chow 5140, which had an analysis of 32% crude protein. Feed composition was previously reported (McMurtry et al., 1990a). The rate of daily feed application was based on fish biomass as influenced by age and mean individual weight. Standing fish biomass and feed rates were adjusted monthly (McMurtry et al., 1990a).

Irrigation water was drawn from the bottom of the fish tanks 8 times daily between dawn and sunset and pumped to the biofilter surface at 5001 m-2 d-1 (McMurtry et al., 1990a, 1990b). Tanks were recharged with city water equal to evapotranspiration losses when tank volumes were 75% capacity. The number of recycled water applications for the fish crop per unit volume was calculated from the percent tank exchange per day multiplied by the duration of the respective fish culture interval.

The number of water applications to the vegetable crops was calculated from the number of irrigation events per day multiplied by the duration of the respective vegetable cropping interval. The sum of applications per total water used was calculated as twice the volume moved (2 crops) divided by the total volume used. Biofilter nutrient amendment, make-up water due to evapotranspiration and leakage, the number of fish, their biomass at stocking, the total feed input, mean standing fish biomass, and the fish biomass increase during the crop interval were previously reported (McMurtry et al., 1990a, 1990b).

Vegetable seedlings were transplanted into each biofilter at 4 plants m-2 resulting in 4, 6, 9, or 14 plants per biofilter (McMurtry et al., 1990a). Tomato fruit were harvested at the incipient color stage (McMurtry et al., 1990b) and cucumber fruit were harvested when they attained 5 cm in diameter.

The soil-borne bacterial pathogen Pseudomonas solanacearum (Smith) Smith was anticipated from preliminary studies and preplant fumigation of the sand with methyl bromide-chloropicrin (98-2 v/v) was made at 250 kg ha-1.

Insect pests were controlled principally through the use of beneficial insects, including Encarsia formosa Gahan and Chrysopa carnea Stephens for greenhouse whitefly (Trialeurodes vaporariorum (Westwood)), and Hippodamia convergens (Guerin-Meneville) for potato aphid (Macrosiphum euphorbiae (Thomas)). Safer’s™ Insecticidal Soap was applied as necessary to maintain Sweetpotato whitefly (Bemisia tabaci (Gennadius)) populations below threshold levels.

Shrews (Blarina spp.) inhabited the greenhouse during the winter cucumber crop. Spring traps were ineffective in controlling damage to developing fruitlets. Installation of an in-ground subsonic alarm (Go’pher It™) purged the greenhouse of this pest.

The edible portion of fish biomass produced was calculated as 50% of the increase in live weight. Caloric content of the edible fish biomass was calculated at 1.02 cal g-1 (Anon. 1975). The protein fraction was calculated at 18.2% of the edible portion (Anon. 1975).

The edible portion of tomato fruit was calculated as 100% of the Grade No. 1 and Grade No. 2 yields. Caloric content of the tomato fruit was calculated at 0.22 cal g-1 (Lorenz and Maynard 1980). The protein fraction was calculated at 1.1% of the edible yield (Lorenz and Maynard, 1980).

Annualized fish growth rates in each treatment ratio were estimated from linear regressions of the mean individual increases in fish weight from 14 g to 214 g and from 14 g to 442 g on time.

Economic yields for fillets were calculated for the 214 g fish at 40% live weight with a market value of $3.00 kg-1 and for the 442 g fish at 50% live weight with a market value of $4.40 kg-1.

Annualized yield of ‘Laura’ tomato in each treatment was estimated for trusses 1-8 at twice the mean yield of trusses 1-4 (McMurtry et al., 1990b) with 3 crops grown per year. Annualized yield for ‘Kewalo’ tomato in each treatment was estimated at 3 times the yield of trusses 1-8 (McMurtry et al., 1990b) for 3 crops yr-1.

Fruit quality grade distribution was assumed to be 60% Grade No. 1, 30% Grade No. 2, and 10% cull at $2.20, $1.32, and ($0.05) per kg, respectively. Production value per composite unit area was calculated from the addition of the gross values returned from 442 g fish and the respective tomato crops divided by the combined fish tank and biofilter area of each treatment ratio.

The experiments were conducted as a randomized complete block design with four replicates. Multiple daily observations were averaged. Analyses for factorial experiments were made with Statview™ 512+ on a PC. One factor multi-comparison ANOVA tests were conducted for significance levels of P ≤ 0.05, 0.01, and 0.005. When F-test warranted, LSD were calculated.

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Olericulture was integrated with recirculatory aquaculture in a greenhouse in Raleigh, NC (McMurtry et al., 1990a, 1990b, 1990c). All-male (sex-reversed) hybrid tilapia (Oreochromis mossambicus (Peters) x O. niloticus (L.)) were cultivated in tanks which were physically associated with a biofilter utilizing builders’ grade sand as substrate (McMurtry et al., 1990a).

Irrigation water was drawn from the bottom of the fish tanks 8 times daily between dawn and sunset and pumped to the biofilter surface at 5001 m^-2 d^-1 (McMurtry et al., 1990a, 1990b). Tanks were recharged with city water equal to evapotranspiration losses when tank volumes were 75% capacity. The number of recycled water applications for the fish crop per unit volume was calculated from the percent tank exchange per day multiplied by the duration of the respective fish culture interval.

Biofilter nutrient amendment, make-up water due to evapotranspiration and leakage, the number of fish, their biomass at stocking, the total feed input, mean standing fish biomass, and the fish biomass increase during the crop interval were previously reported (McMurtry et al., 1990a, 1990b).

Vegetable seedlings were transplanted into each biofilter at 4 plants m^-2 resulting in 4, 6, 9, or 14 plants per biofilter (McMurtry et al., 1990a). Tomato fruit were harvested at the incipient color stage (McMurtry et al., 1990b) and cucumber fruit were harvested when they attained 5 cm in diameter.

The soil-borne bacterial pathogen Pseudomonas solanacearum (Smith) Smith was anticipated from preliminary studies and preplant fumigation of the sand with methyl bromide-chloropicrin (98-2 v/v) was made at 250 kg ha^-1.

Insect pests were controlled principally through the use of beneficial insects, including Encarsia formosa Gahan and Chrysopa carnea Stephens for greenhouse whitefly (Trialeurodes vaporariorum (Westwood)), and Hippodamia convergens (Guerin-Meneville) for potato aphid (Macrosiphum euphorbiae (Thomas)).

Safer’s™ Insecticidal Soap was applied as necessary to maintain Sweetpotato whitefly (Bemisia tabaci (Gennadius)) populations below threshold levels. Shrews (Blarina spp.) inhabited the greenhouse during the winter cucumber crop. Spring traps were ineffective in controlling damage to developing fruitlets. Installation of an in-ground subsonic alarm (Go’pher It!™) purged the greenhouse of this pest.

The edible portion of fish biomass produced was calculated as 50% of the increase in live weight. Caloric content of the edible fish biomass was calculated at 1.02 cal g^-1 (Anon. 1975). The protein fraction was calculated at 18.2% of the edible portion (Anon. 1975). The edible portion of tomato fruit was calculated as 100% of the Grade No.1 and Grade No. 2 yields. Caloric content of the tomato fruit was calculated at 0.22 cal g^-1 (Lorenz and Maynard 1980). The protein fraction was calculated at 1.1% of the edible yield (Lorenz and Maynard, 1980).

Annualized fish growth rates in each treatment ratio were estimated from linear regressions of the mean individual increases in fish weight from 14 g to 214 g and from 14 g to 442 g on time. Economic yields for fillets were calculated for the 214 g fish at 40% live weight with a market value of $3.00 kg^-1 and for the 442 g fish at 50% live weight with a market value of $4.40 kg^-1.

Experiment 1

Fish were stocked on 5 May 1988 at a uniform stocking density, mean individual weight, and total biomass (McMurtry et al., 1990a). Tomato (Lycopersicon esculentum Mill. ‘Laura’) was transplanted 13 May 1988 and grown as a single stem (McMurtry et al., 1990b, 1990c). Fruit was set only on trusses 1-4 because of excessive heat (40°C+) after 22 June (McMurtry et al., 1990b).

Experiment 2

Fish were stocked on 25 August 1988 at a uniform density, mean individual weight, and total biomass (McMurtry et al., 1990a). The system was irrigated and fish feeding continued for 42 days without plants grown in the biofilters to assess whether or not plants were contributing to pH buffering of the water (McMurtry et al., 1990a).

Water pH fell rapidly to below pH 4.0 and incremental amendments with CaMg(CO₃)₂ were made totaling 2.0 kg per biofilter in an effort to raise water pH and reestablish nitrification prior to replanting (McMurtry et al., 1990a).

The fish were harvested 42 days after stocking and biomass per tank was adjusted to uniformity across treatments by removal of the largest individuals in appropriate tanks prior to replanting of the biofilters (McMurtry et al., 1990a).

A parthenocarpic greenhouse cucumber (Cucumis sativus L. ‘Fidelio’) was transplanted 22 September 1988 and grown as a single stem (McMurtry et al., 1990a). Water pH was considered too low for proper nutrient assimilation by cucumber and CaO was added approximately twice weekly in quantities sufficient to raise water pH above 6.5 following each application (McMurtry et al., 1990a).

Experiment 3

Fish were stocked 5 Jan 1989 at a uniform density, mean individual weight, and total biomass (McMurtry et al., 1990a). The semi-determinate, bacterial wilt-resistant tomato ‘Kewalo’ was planted 5 January, 1989 and grown as a single stem (McMurtry et al., 1990b, 1990c).

Results

Experiment 1

The number of total fish applications (tank volume exchanges) of recycled water increased with BFV due to the fixed irrigation rate per unit biofilter area (Table 2a). The number of water applications to the plant crop was identical in all treatments. The sum of crop applications per liter of total water used increased with BFV. Fish biomass increase per liter of total water used decreased with increasing BFV, while fruit yield per liter of total water used increased with BFV.

Both calories and edible protein per unit of total water used decreased with BFV for fish yield and increased with BFV for tomato yield (Table 3a). Total calories per unit water used did not differ by treatment. Total protein in the fish and tomatoes per liter of total water used decreased with increasing BFV. Irrespective of water usage, both total calories and protein in the fish and tomatoes increased with BFV.

Experiment 2

Total water inputs increased with BFV (Table 2b). Make-up water for evapotranspiration and seepage losses increased with BFV and ranged from 1.2% to 2.7% system capacity per day (data not shown). The number of recycled water applications to the fish tanks increased with BFV due to the fixed irrigation rate per unit biofilter area (Table 2b).

The number of applications of water to the plants was identical in all treatments. The sum of water applications to the crops per liter of total water used generally increased with BFV. The decline in the sum of crop applications per total volume used in the 1:2.25 v/v ratio was attributed to seepage losses in two of these plots.

Fish biomass increase per liter of total water used tended to decrease with increasing BFV. Cucumber fruit yields per liter of total water used were not significantly different. This was attributed to low pH of the water following the ‘no crop’ interval (McMurtry et al., 1990a). Calories in the calculated increase in fish biomass per liter of total water decreased with increasing BFV.

Calories of the cucumber fruit did not differ with BFV (Table 3b). The total energy represented in the combined outputs per liter of total water did not differ with BFV. The calculated protein content of the edible portion of fish biomass increase per liter of total water generally decreased with increasing BFV. Protein content of the cucumber fruit did not differ with BFV.

Total protein represented in the combined outputs per liter of total water did not differ with BFV. Both total caloric value and total protein represented in the combined outputs increased with BFV irrespective of water consumption.

Experiment 3

Total water inputs increased with BFV (Table 2c). Make-up water for evapotranspiration and seepage losses increased with BFV and ranged from 2.6% to 4.7% system capacity per day (data not shown).

The number of total fish applications of recycled water increased with BFV due to the fixed irrigation rate per unit biofilter area (Table 2c). The number of plant crop applications of water was identical in all treatments. The sum of crop applications per liter of total water used increased with BFV.

Fish biomass increase per liter of water used decreased with increasing BFV while fruit yield increased with BFV except for in the 1:2.25 v/v ratio treatment which was attributed to seepage losses. Calories of the increase in fish biomass decreased with increasing BFV while calories in tomato fruit were not affected by BFV (Table 3c). Total calories per unit water used did not differ with treatment.

Edible protein of the fish biomass increase per unit of total water used decreased with increasing BFV while protein production per liter of total water used for tomato fruit did not differ. Total protein in the fish and tomatoes per liter of water differed only between the 1:2.25 v/v biofilter ratio and each other ratio. Irrespective of water consumption, both total calories and protein in the fish and tomatoes increased with BFV.

Annualized fish production rates for 214 g and 442 g market size fish are given in Table 4. Corresponding market values per unit tank volume were estimated to range $63 to $77 m-3 yr-1 for 214 g fish (data not shown) and $91 to $112 m-3 yr-1 for 442 g fish.

Annualized yields for tomato ‘Laura’ and ‘Kewalo’ decreased with BFV (Table 4). The combined value of annualized fish and ‘Laura’ tomato production per composite unit area ranged from $124 to $98 m-2 (Table 4). Substitution of ‘Kewalo’ tomato for ‘Laura’ resulted in production value ranging from $99 to $56 m-2 yr-1 (data not shown).

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Experiment 1

Elemental composition and pH of the water after a year of continuous operation are given in Table 1. Total water inputs increased with BFV (Table 2a). Make-up water for evapotranspiration and seepage losses increased with BFV and ranged from 1.7% to 3.2% system capacity per day (data not shown). The number of total fish applications (tank volume exchanges) of recycled water increased with BFV due to the fixed irrigation rate per unit biofilter area (Table 2a). The number of water applications to the plant crop was identical in all treatments.

The sum of crop applications per liter of total water used increased with BFV. Fish biomass increase per liter of total water used decreased with increasing BFV, while fruit yield per liter of total water used increased with BFV.

Experiment 2

Cucumber fruit yields per liter of total water used were not significantly different. This was attributed to low pH of the water following the ‘no crop’ interval (McMurtry et al., 1990a).

Calories in the calculated increase in fish biomass per liter of total water decreased with increasing BFV. Calories of the cucumber fruit did not differ with BFV (Table 3b). The total energy represented in the combined outputs per liter of total water did not differ with BFV. The calculated protein content of the edible portion of fish biomass increase per liter of total water generally decreased with increasing BFV.

Protein content of the cucumber fruit did not differ with BFV. Total protein represented in the combined outputs per liter of total water did not differ with BFV. Both total caloric value and total protein represented in the combined outputs increased with BFV irrespective of water consumption.

Experiment 3

Total water inputs increased with BFV (Table 2c). Make-up water for evapotranspiration and seepage losses increased with BFV and ranged from 2.6% to 4.7% system capacity per day (data not shown). The number of total fish applications of recycled water increased with BFV due to the fixed irrigation rate per unit biofilter area (Table 2c).

The number of plant crop applications of water was identical in all treatments. The sum of crop applications per liter of total water used increased with BFV. Fish biomass increase per liter of water used decreased with increasing BFV while fruit yield increased with BFV except for in the 1:2.25 v/v ratio treatment which was attributed to seepage losses.

Calories of the increase in fish biomass decreased with increasing BFV while calories in tomato fruit were not affected by BFV (Table 3c). Total calories per unit water used did not differ with treatment. Edible protein of the fish biomass increase per unit of total water used decreased with increasing BFV while protein production per liter of total water used for tomato fruit did not differ.

Total protein in the fish and tomatoes per liter of water differed only between the 1:2.25 v/v biofilter ratio and each other ratio. Irrespective of water consumption, both total calories and protein in the fish and tomatoes increased with BFV.

Annualized fish production rates for 214 g and 442 g market size fish are given in Table 4. Corresponding market values per unit tank volume were estimated to range $63 to $77 m^-3 yr^-1 for 214 g fish (data not shown) and $91 to $112 m^-3 yr^-1 for 442 g fish. Annualized yields for tomato ‘Laura’ and ‘Kewalo’ decreased with BFV (Table 4).

The combined value of annualized fish and ‘Laura’ tomato production per composite unit area ranged from $124 to $98 m^-2 (Table 4). Substitution of ‘Kewalo’ tomato for ‘Laura’ resulted in production value ranging from $99 to $56 m^-2 yr^-1 (data not shown).

Discussion

Fruit yield per biofilter increased with BFV (McMurtry et al., 1990b) suggesting increased efficiency of nutrient extraction from aquaculture effluents with increasing plant number per unit fish or unit feed input. Yield per plant increased with decreasing BFV (McMurtry et al., 1990b), indicating greater per plant nutrient availability. This finding supports an earlier observation of greater per plant uptake of most nutrients with decreasing BFV (McMurtry et al., 1990c).

Plant uptake of anions and cations helped buffer water pH (McMurtry et al., 1990a). Plant growth was adequately maintained on minimal nutrient levels due to the constant replenishment characteristic of recirculated aquacultural water (Lewis et al., 1978; Winsor et al., 1985).

As in any system, only one dependent variable can be optimized. If optimal use of nutrient inputs is sought, a high plant number to unit fish biomass appears preferable. However, fruit yield per plant was greatest at low plant population per unit fish biomass production (McMurtry et al., 1990b).

Additionally, total protein output per liter of water tended to be higher with smaller BFV. If maximal fish production per composite unit area is sought, a low plant population per unit of fish biomass production is required. Total calories produced per unit water used did not change with biofilter ratio which is a reflection of identical fish food inputs.

The pH of the water remained below 7.0 indicating that the largest percentage of the ammonia resulting from fish metabolism remained in ionized form (non-toxic to fish). Subsequent microbial conversions and plant assimilation of nitrogenous compounds maintained water quality suitable for tilapia production (McMurtry 1990a). When N assimilation rates approximate N input rates, alkaline amendment is not necessary in this system (McMurtry 1990a).

Uniform crop development and satisfactory performance of this system can be attributed in part to the reciprocating water movement, which ensured even distribution of nutrients and O2 to all plants by drawing atmospheric O2 through the medium during every drainage period (McMurtry et al., 1990b). This co-culture technique appears to have greater potential for profit than traditional commercial greenhouse tomato production which is valued at $62 m-2 yr-1 under identical fruit quality distribution and market value assumptions.

The combination of aquaculture and olericulture provides opportunity to increase profitability by reducing direct production costs relative to both current systems operated separately. The culture system employed in these studies is simple to operate. Fish stocking density and feed rates are adjusted to optimize water quality as influenced by plant growth rate.

Plants are grown using traditional methods excluding any which are harmful to either fish, plants, or biofilter microbes. Water quality must be monitored regularly to provide a basis for management decisions.

Plants should be grown in the biofilters on a continuous basis. This may be accomplished through rotational multicropping. This polytrophic culture system has substantial potential in areas of limited water supply and/or high land value.

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If maximal fish production per composite unit area is sought, a low plant population per unit of fish biomass production is required. Total calories produced per unit water used did not change with biofilter ratio which is a reflection of identical fish food inputs.

This co-culture technique appears to have greater potential for profit than traditional commercial greenhouse tomato production which is valued at $62 m^-2 yr^-1 under identical fruit quality distribution and market value assumptions. The combination of aquaculture and olericulture provides opportunity to increase profitability by reducing direct production costs relative to both current systems operated separately.

The culture system employed in these studies is simple to operate. Fish stocking density and feed rates are adjusted to optimize water quality as influenced by plant growth rate. Plants are grown using traditional methods excluding any which are harmful to either fish, plants, or biofilter microbes.

Water quality must be monitored regularly to provide a basis for management decisions. Plants should be grown in the biofilters on a continuous basis. This may be accomplished through rotational multicropping. This polytrophic culture system has substantial potential in areas of limited water supply and/or high land value.

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Watten, B.J., and R.L. Busch. 1984. Tropical production of tilapia (Sarotherodon aureus) and tomatoes (Lycopersicon esculentum) in a small-scale recirculating water system. Aquaculture 41:271-283.

Welcomme, R.L. 1977. Inland fisheries in arid zones. pp. 303-306 In: E. Barton Worthington (ed.). Arid Land Irrigation in Developing Counties: Environmental Problems and Effects. Pergamon Press, Oxford, England. 463 p.

Winsor, G. W., R.G. Hurd and D. Price. 1985. Nutrient Film Technique. 2nd Ed. Glasshouse Crops Research Institute. Growers Bulletin No. 5, Littlehampton, England. 59 p.

World Commission on Environment and Development. 1987. Our Common Future. Oxford University Press, Oxford, England. 383 p.

Additional Citations;

Rakocy, J.E., Masser, M.P., & Losordo, T.M. (2006). Recirculating Aquaculture Tank Production Systems: Aquaponics—Integrating Fish and Plant Culture. SRAC Publication No. 454.

Somerville, C., Cohen, M., Pantanella, E., Stankus, A., & Lovatelli, A. (2014). Small-scale aquaponic food production: Integrated fish and plant farming. FAO Fisheries and Aquaculture Technical Paper No. 589. Rome, FAO.

Love, D.C., Fry, J.P., Li, X., Hill, E.S., Genello, L., Semmens, K., & Thompson, R.E. (2015

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