Performance of an Integrated Aquaculture-Olericulture System as Influenced by Component Ratio

Water Quality Maintenance and Mineral Assimilation by Plants Influence Growth of Hybrid Tilapia in Culture with Vegetable Crops 

M.R. McMurtry, D.C. Sanders and R.G. Hodson,S Department of Horticultural. Science and UNC Sea Grant Program, North Carolina State University, Raleigh, NC 27695 

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


Fish and vegetable production were linked in a recirculating water system. Hybrid tilapia (Oreochromis mossambicus (Peters) x 0. niloticus (L.)) was grown in tanks and fed a 32% protein feed. Tomato (Lycopersicon esculentum Mill. ‘Laura’) was grown in summer 1988, cucumber (Cucumis sativus L. cFidello’) in fall 1988, and tomato’Kewalo’ in spring 1989 in a Raleigh, N.C., greenhouse.

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

Dissolved oxygen levels, make-up water, fish biomass and fish growth rates increased with biofilter volume. Total arornoniacal-N, N0 2-, and N03- concentrations decreased with increasing biofilter volume~ Water pH declined rapidly when the system was operated without plants. When plants grew nor1nally, water pH remained stable at approximately pH 6.0 if feed rates were not excessive.

Fruit yields per fish biomass increase and per biofilter increased with biofilter volume. Fruit yields and fish biomass increase per plant declined with increasing biofilter volume. Fish growth associated with the largest bioftlter was 120% that associated with the smallest biofilter.


Benefits of integrating aquaculture and olericulture are: 1) conservation of water resources and plant nutrients (McMurtry et al. 1990c, 1990d), 2) intensive production of fish protein and 3) reduced operating costs relative to either system in isolation. The constraints of water supply, soil type and land availability do not limit the use of recirculating systems as occurs in pond or cage aquaculture (Rakocy 1989a).

Water consumption in integrated systems including tilapia production is less than 1 % of that required in pond culture to produce equivalent yields (Rakocy 1989b; McMurtry 1990d). Such a symbiotic system is applicable to the needs and req11irements of arid or semi-arid regions where fish and fresh vegetables are in high demand (Nair et al. 1985; Rakocy 1989b; McMurtry et al. 1990e).

Organic vine-ripened, pesticide-free produce and ‘fresh-daily’ fish can bring premium prices, panicularly during winter months in urban areas. Markets for fresh fish abound in landlocked regions and overfished coastal areas throughout the world (Nair et al. 1985; Rakocy 1989b).

Recirculating aquaculture water has been used for hydroponic cultivation of higher plants (Lewis et al. 1978; Nair et al. 1985; Rakocy 1989a, 1989b). Previous integrated systems have removed more than 95% of the suspended solids from the water by sedimentation in clarifers prior to plant application (Rakocy 1989b).

Hydroponic vegetable production controlled N03- concentrations in recirculating aquaculture water (Lewis et al. 1978; Nair et al. 1985; Kane 1987; Rakocy 1989a), and eliminated the need for microbial denitrification. Biofilters that are alternately flooded and drained were first proposed by Lewis et al. (1978) and are called reciprocating bioftlters (RBF).

Advantages of a RBF are 1) • unifo1111 distribution of nutrient-laden water within the flltration medium during the flood cycle and 2) improved aeration of the bioftlter from atmosphere exchange with each dewatering (Lewis et al. 1978; Paller and Lewis 1982; Nair et al. 1985; Rakocy 1989a) . • 4 Nitrification is limited by oxygen concentrations lower than 2 mg L-1.(Nair et al. 1985) and complete oxidation of 1 mg of NH3-N requires 4.6 mg of oxygen (Kaiser and Wheaton 1982). RBF’s benefit nitrifying bacteria and plant roots (Lewis et al. 1978; Rakocy 1989a, 1989b ).

Management of integrated systems includes maintenance of a nutrient balance to maximize both fish and plant yields (Rakocy 1989b). The objective of this study was to evaluate the influence of fish tank to bioftlter volume (BFV) ratio on fish growth rate and water quality. 

Materials and Methods 

All male (sex-reversed) hybrid tilapia (Oreochromis mossambicus (Peters) x O. niloticus (L.), Cichlidaceae) were cultivated in 500 liter in-ground tanks with aeration provided by regenerative blowers at 0.7 L·s- 1 through two (3.8 x 3.8 x 15 cm.) airstones per tank.

Water temperatures were kept above 25°C by two Visithe1m™ 250W the1mostatic aquaria heaters per tank. The rectangular tanks were fon11ed with plywood, the bottom sloped to 45° and lined with 0.50 mm (2@ 10 mil.) black polyethylene (Fig. 1 ).

Each tank was coupled to a biofilter employing a builder’s grade sand as substrate. Tanlc water level at capacity was 10 cm below the bottom of the biofilter. Biofilters were 1.2 m wide, 0.33 m deep and of variable length to achieve 4 ratios by volume to the fish tank (Table 1). Biofilters were lined with 0.45 mm (three @ 6 mil.) polyethy!ene plastic and the bottom sloped I : 200 along the length to direct drainage for return to the associated tank

Media composition was 99.25% quartz sand, 0.75% clay, 0.0% silt. The sand fractionation was: very fme sand, 1.1 %; fine sand, 5 .2%; medium sand, 21.0%; coarse sand, 38.8%; and very coarse sand, 33.3%.

Four tank to BFV ratios, bracketing that used in preliminary studies, were selected as treatments (McMurtry et al. 1990d). • 5 Experiments were conducted in a greenhouse in Raleigh, N.C.

Infection with the soil-borne bacterial pathogen Pseudomonas solana.cearwn (Smith) Smith was anticipated from preliminary studies and preplant fumigation of the sand with methyl bromidechloropicrin (98-2) was made at 250 kg ha- 1. Each bioftlter was inoculated with 1.0 liter of Fritz-zyme #7 (a suspension of Nitrosomonas Winogradsky sp. and Nitrobacter Winogradsky sp.), and irrigated with aquaculture effluents for nine days prior to planting the frrst vegetable crop. Tomato (Lycopersicon esculentum Mill.) or cucumber (Cucumis sativus L.) seedlings were transplanted into each biofilter at four plants m-2 in each study.

Plant populations were 4, 6, 9, or 14 plants with increasing BFV. The fish were fed a diet of modified Purina Fish Chow 5140, with a minimum analysis of 32% crude protein, 3.5% crude fat, and not more than 7 .0% crude fiber. The feed was not fortified with vitamins or trace elements (Table 2). The daily feed input rate was based on a percentage of standing fish biomass as influenced by age and mean individual weight (Pullen and Lowe-McConnell 1982).

The daily ration was divided equally into two feedings administered at 0800 and 1300 hours. The fish also grazed algae (Oscillatoria Vaucher spp., Cyanophyta and Ulothrix Klitzing spp., Chlorophyta) which grew in the water and on the tank sides. Fish food was analyzed using atomic absorption spectrophotometry for K, Ca, Mg, Fe, Mn, Zn, and Cu, vanadomolybdophosphoric yellow procedure (Jackson 1958) for P, Kjeldahl procedure (Black et al. 1965) using a salicylic acid modification for N, a curcumi~ method (Grinstead and Snider 1967) for B, and a turbidanetric procedure (Hunter 1979) for S.

Analyses are reported on a dry weight (DW) basis. Irrigation water was pumped from the bottom of the fish tan.ks eight times daily and delivered to the biofilter surfaces at a rate of 500 L m-2 of bioftlter surface per day.

The water flooded the biofilter surfaces, percolated through the medium, and drained back to the fish tank. The tank water level dropped approximately 25 cm during each irrigation • 6 event. Therefore, the returning water therefore provided additional aeration. Biofilters drained intensively for approximately 15 min. and at a diminished rate for one hour.

Evapotranspiration losses were replaced weekly with city water. Input water composition and pH were reported by McMurtry et al.(1990d). Water pH, and temperature measurements were made in situ at random times daily with an Orion SA250 A TC pH meter using a Fisher double-junction pH electrode and . Orion ATC probe. Diurnal modulation of pH, temperature, total ammoniacal-N (TAN), N02-, and N03- levels were assayed weekly.

The tank water was sampled prior to each filtration event, irrigate sampled during each filtration event, and biofilter drainage sampled prior to tank return. V aloes obtained from the random assays were compared with those taken at the same hour in the diurnal sampling of the same week. Water samples of 120 ml were drawn at the time of each water pH assay from the top of each tank, titrated to pH 2.0, sealed and stored at 5°C for up to two weeks prior to assays for nitrogenous compounds. Aqueous TAN and N02 .. concentrations were assayed on an Orion SA270 Ion Specific Electrode (ISE) meter using Fisher NH(3+4) and N0 2-, ISE electrodes. Aqueous N03- concentrations were assayed on an Orion Research Ionalyzer model 407 A meter with a Fisher N03 – ISE electrode and/or were verified using a modified salicylic acid and NaOH colorimetric procedure (Cataldo et al. 1975.) with a Beckman model DB-G grating spectrophotometer. Dissolved oxygen (DO) measurements were made at 0730 and 1300 hours in situ with an Otterbine Barebo 111 DO mete_r at least weekly. Methyl orange alkalinity was dete1·mined by titration. Fish biomass was deterrnined after removal of all fish from the tank.

The fish were sedated with Quinadine, blotted dry, and weighted individually. Fish biomass increase per time interval was calculated by subtraction of the respective stocked biomass. Fish were returned to the same tank with adjustments made (fish added or removed) to maintain unifo11n (±2.5%) biomass. Feed conversion ratio (FCR), monthly production • • 7 rate (MP), monthly specific growth rate (MSG) and the daily rate of increase in biomass (DRIB) were calculated. The experiments were conducted as a randomized complete-block design with four replicates.

Analyses of variance were made for factorial experiments with Statview™ 512+ on a personnal computer. When F-test warranted, LSDs were calculated.

Experiment 1 

Fish were stocked on 5 May 1988 at a unifo11n stocking density, mean individual weight (Pmi), and initial biomass (Bi) as seen in Table 3a. An initial feeding rate of 4.3% of Bi d-1 was increased when inputs were consumed within 15 minutes.

Daily feed input increased with fish biomass and was 2.2 % of frnal biomass (Br) per day at harvest 99 days from stocking. Tomato ‘Laura’ was transplanted into the bioftlters on 13 May 1988. This indeterrninate greenhouse variety was grown as a single-stem.

Fruit were harvested at the incipient color stage (McMurtry et al. 1990b, 1990c). The crop was terminated after harvest at four trusses.

Experiment 2 

Fish were restocked on 25 August 1988 so that expected Br during the succeeding interval would be lower than the 17 kg m-3 occurring in Experiment 1. Stocking densities, Pmi, and Bi are given in Table 3b. A feed rate of 5.0o/o of Bi d-1 was maintained until the fish were harvested after 42 days.

The system was operated for 42 days without plants grown in the bioftlters to assess whether or not plants were contributing to pH buffering of the water . • Incremental additions of CaMg(C03) 2 were made to each bioftlter after water pH fell below pH 4.0 in order to raise water pH and reestablish nitrification.

Fish biomass per tank was equalized across treatments by removing the largest individuals in appropriate tanks prior to replanting the biofilters. Feed input rate was adjusted to 3.4% of Bi d-1 and maintained until fish were harvested at 85 days from • 8 restocking. Cucumber ‘Fidello’ was transplanted into the bioftlters on 22 September 1988 and pruned to a single-stem. Following CaMg(C03) 2 inputs, water pH in most tanks remained below pH 6.0 which was deemed too low for balanced nutrient assimilation by cucumber. Therefore, CaO was added to the tank water approximately twice weekly in quantities sufficient to raise water pH in each tank to above 6.5 following each application. 

Experiment 3 

Fish were stocked on 5 January 1989 at a unifo1·m stocking density, Pmi, and Bi as seen in Table 3c. An initial feed rate of 1.8% of Bi d-1 was reduced gradually when feed remained uneaten for more than 15 minutes. Fish were harvested 132 days from stocking.

The semi-determinate, bacterial wilt-resistant tomato ‘Kewalo’ was planted 5 January, 1989 and grown as a single-stem (McMurtry et al. 1990b, 1990c). Fruit were harvested at the incipient color stage.


Experiment 1 

Mean fish growth rate (G) and total biomass increase increased with increasing BFV while the MSG and DRIB were not significantly different but tended to increase with BFV (Table 3a). Mean FCR tended to decrease as BFV increased.

Mean individual size at harvest (Pmr) was not different among treatments while Bt and MP di.ff ered ~ong treatments. Diurnal mean DO concentration increased as water temperature decreased with increasing BFV (Table 4a). Water DO concentrations ranged from 4.8 and 7.8 mg L-1 with minimal day to day variation (data not shown).

Total alkalinity increased from 40 mg L-1 in week 1 to 180 mg L-1 by week 5, but remained stable through week 8 and was not assayed thereafter (data not shown). • 9 The TAN and N0 2 • concentrations decreased with increasing BFV (Table 4a). Initial TAN concentrations increased from 0.0 mg L •1 over the first 7 weeks to mean high levels ranging from 10.8 to 30.2 mg L-1 with decreasing BFV (data not shown). Initial N0 2- concentrations increased from 0.0 mg L· 1 over the first 4 weeks to mean high levels ranging from 3.0 to 8.1 mg L-1 with decreasing BFV (data not shown). At te1·111ination of the tomato crop, TAN and N02- concentrations ranged from 0.7 to 1.1 mg L-1 and 0.02 to 0.07 mg L-1 , respectively (data not shown).

Mean water pH generally decreased with increasing BFV (Table 4a). Water pH increased from pH 6.5 to 7 .4 in each treatment over the first 2 weeks as bacterial and plant populations became established (data not shown).

Water pH declined to approximately pH 6.0 in all treatments by week 5 and remained stable through tetntlnation of the tomato crop (data not shown). Total make-up water increased with BFV and water consumption per unit bioftlter area declined with increasing BFV (Table 4a). No amendments were made to adjust water pH.

Experiment 2 

Water pH declined rapidly from approximately pH 6.0 in all treatments to pH 4.3 or less during the interval with no crop in the biofilters (data not shown). Subsequent CaMg(C03) 2 amendment, given in Table 4b, raised the mean pH to 5.5 or greater (data not shown).

The mean fish biomass increase ranged from 1.88 to 3.04 kg m-3 and G ranged 1.85 to 2 .. 74 g fish-1 ct-1 at 42 days from stocking. The FCR ranged from 1.43 to 3.50, but there was no consistent trend with BFV (data not shown).

The ending feed input rate was 3.1 % of Br a-1. Water pH at terrnination of the cucumber crop was pH 6.0, 5.5, 5.8, and 6.4 with increasing BFV, respectively (data not shown). Cucumber yield per biofilter was 11.18, 10.04, 11.41, and 33.32 kg and yield per plant was 2.80, 1.67, 1.27, and 2.38 • 10 kg with increasing BFV, respectively (data not shown). Co11elation of diurnal mean pH and fruit yield per biofilter within treatments were 0.992, 0.901, 0.968, and 0.928 with increasing BFV, respectively (r2= 0.984, 0.812, 0.937, and 0.861 with P= 0.008, 0.099, 0.032 and 0.072, respectively).

Feed input rate at day 85 from transplant of cucumber was 1.0% of Bt d- 1. Composite 127 day fish growth rates (G, MSG and DRIB) and fish biomass increase tended to increase with BFV (Table 3b). Composite 127 day FCR tended to decrease as BFV increased. Mean Pmr did not differ between any treatment combination. The Br and the MP rate increased with BFV through the 1:.1 .. 50 v/v ratio Mean water temperature generally declined with increasing BFV (Table 4b). Differences in water pH were not related to BFV.

Total make-up water increased with BFV and water consumption per unit area declined with increasing BFV. Lime amendment was identical across treatments while CaO amendments were inversely proportional and negatively correlated to mean water pH over time (CV= -4.84, CR= –0.82, r2= 0.673, P= .0001 ).

Experiment 3, 

The G, MSG, and DRIB rates did not differ significantly but tended to increase with BFV (Table 3c). The FCR in response to BFV was inconsistent. The fish biomass increase, Br and MP did not differ among treatments. The feed input rate at day 77 was 0.9o/o of Bi d-1 and was 0.6% of Br d~l by the end of the 132 day feeding regime (data not _shown). The DO levels increased with BFV (fable 4c).

Water DO concentrations ranged from 5.6 and 6.1 mg L-1 with minimal day to day variation (SD=0.31, data not shown). Water temperature decreased with increasing BFV·(fable 4c). The TAN, N02· and N03- concentrations decreased with increasing BFV (fable 4c). Mean N03- concentrations differed between the l; 2.25 v/v treatment ratio and each • • 11 other ratio. The TAN and N02- concentrations irutially ranged from 0.03 to 0.20 mg LI and 0.05 to 0.10 mg L-1 , respectively, and increased over 2 and 10 weeks to mean high levels ranging 1.18 to 1.49 mg L- 1 and 0.06 to 0.35 mg L- 1 , respectively, with decreasing BFV (data not shown).

At peak tomato harvest the TAN and N02- concentrations ranged from 0.29 to 0.32 mg L-1 and 0.06 to 0.09 mg L- 1 , respectively, with decreasing BFV (data not shown). The N03- concentrations increased with BFV, initially ranged 88 to 230 mg L- 1 , increased for 2 weeks to a range of 99 to 246 mg L- 1 , and at peak tomato harvest had declined to 30 to 241 mg L-1 (data not shown).

Mean water pH tended to increase with BFV but differences were not significant because CaO inputs were made to maintain levels above pH 6.0 (Table 4c). Total makeup water increased with BFV and water consumption per unit area declined with increasing BFV. Water pH had remained low following Experiment 2 and weekly additions of CaO were made until pH remained above pH 6.0 in all treatx11ents (data not shown).

Total CaO input to each tank was negatively co11elated to mean pH (CV = -13.04, CR.= -0.86, r2 =0.732, P= .0001) (Table 4c). Water pH remained stable through termination of the tomato crop following the CaO inputs (data not shown). 

Total Fish Growth and Mean Water Quality in Experiments 1, 2 and 3, 

The fish biomass increase in all experiments and the G, MSG, and DRIB rates increased or tended to increase with BFV (Table 5). Total fish biomass increase per plant decreased with increasing BFV while cumulative fruit yields per kg fish biomass increase increased with BFV . 

The average water DO concentration increased and temperature, TAN, N0 2-, and N03- decreased with increasing BFV (Table 6). Mean water pH over time was not related to BFV. Total make-up water increased-and water consumption per unit area declined with increasing BFV. Inputs of CaO were negatively correlated to diurnal mean water pH (CV.= -15.14, CR= -0.75, r2= 0.554; P= 0.0009) . 

12 Water drawn from fish tanks for irrigation had TAN and N02- concentrations approximately twice that of the water returning after biofiltration (Fig. 2). The percentage reduction in TAN and N02- concentrations with each filtration event decreased with increasing BFV (data not shown).

Percent reduction in N03 • concentration with each filtration event was much less than TAN or N0 2 – (data not shown)~ Fish growth rates from other recirculatory systems that included plants were compared, contrasting similar Pmi, Pmf and culture intervals (Table 7). Growth rate (G) was negatively co11elated to stocking density, regardless of culture system (Fig. 3). The MP per unit volume regressed on stocking density, but was better in this system than those that removed suspended solids prior to plant application of effluents. Mean MP from the 3 other systems used in this comparison, at a stocking density of 100 m-3, would be 3.0 kg m-3 while similar stocking in this system had a treatment mean MP of 5.8 kg m-3. 


A rapid decline in FCR was observed in the frrst experiment when standing fish biomass exceeded 12 kg m-3 regardless of BFV. Fish were stocked in Experiments 2 and 3 so that expected Br would not exceed 10 kg m-3 in order to minimize the quantity of non-ingested feed.

The differential in fish weight gain between experiments is attributed to the differences in Pmi and stocking density. Fish production in Experiments 2 and 3 was limited by a reduction in number of individuals cultured and by their relatively large Pmf· Growth rate (G) was similar between experiments. Because FCR declines with increasing fish size and/or age (Pullen and Lowe-McConnell, 1982), the feed input per mean standing fish biomass and per fish biomass increase was greater in Experiments 2 and 3 than in Experiment 1 . 

13 Biofiltration maintained water quality at acceptable levels for tilapia. Nitrogenous compounds, which frequently limit production in recirculatory aquaculture (Lewis et al. 1978), never reached toxic levels and were extracted by the plants (McMurtry et al. 1990c).

Yield of both fish and fruit per bioftlter increased with BFV in both studies. Mean fruit yield per biofilter ranged 13.66 to 31.65 kg in Experiment 1 and ranged 19.88 to 33.11 kg with increasing BFV (McMurtry et al. 1990b). Increased nutrient uptake by the plants with increasing yield (McMurtry et al. 1990c) resulted in improved water quality, and therefore, increased fish growth with increasing BFV.

Biofilter mass increased the rate of thex mal energy transfer between the water and filter substrate resulting in lower water temperatures with increasing BFV. Microbial conversions and plant assimilation maintained sub-lethal concentrations of aqueous Ncompounds although the assayed levels were in excess of reported toxicities of 48 h LD50 = 2.4 mg NH3 … N L- 1 (Redner and Stickney 1979) and 0.45 mg N0 2–N L-1 (Balarin and Haller 1982) for tilapia. No clinical signs of nitrite toxicity were detected and the fish grew well.

Traditional recirculatory aquaculture has relied on carbonate inputs to neutralize the acidification (Rakocy 1989b ). Alkaline amendment was not necessary when N input rate approximated N assimilation rates, as in Experiments 1 and 3. This was believed to be due to: 1) nitrification occurring in the biofilters where organic matter accumulated to provide buffering capacity 1 2) both ammoniacal-N and N03–N was available to plants, and 3) plant N uptake was mainly N0 3- which increased alkalinity of the medium. Availability of both N14+ and N0 3- ions buffers nutrient solution pH during plant nutrient assimilation (Haynes and Goh 1978; Noggle and Fritz 1983) and N03- uptake was in exchange for OH- ions or bicarbonate ions produced during respiration (Kirkby and Hughes· 1970; Riley and Barber 1971).

CaO amendments in Experiment 3 were due to residual acidity from Experiment 2. Once water pH was reestablished within an acceptable range for plant growth (pH 6.0~6.5), it • I • 14 remained stable. Buffering of water pH also may be attributed to NJ¾+ reacting with OH· ions released during plant anion adsorption to form NJ¾OH (Noggle and Fritz 1983) or to carbonate and/or bicarbonate ions formed in the reaction of ammonia gas, CO2 and H20 (Berber 1968).

Comparison of growth and production levels between culture systems is complicated by Pmi and Pmt, stocking density, and feed quality. Good tilapia growth rates were attributed panially to water pH remaining below pH 7 .0. The greatest percentage of ammoniacal-N generated in fish metabolism remains non-toxic to fish at pH levels <7.0. Fish would have reduced their feeding activity if pH had increased above pH 7.0 (Rakocy 1989a). Ammoniacal-N concentrations can be regulated by adjusting feed input rate (Rakocy 1989a).

Optimum ratios between feed input rate, standing fish biomass, system water volume, and biofilter volume needs to be established for various combinations of fish and vegetable species (Rakocy 1989b). Uniform crop development and satisfactory perf 01·1nance of this system can be partially attributed to the reciprocating water movement. Muir (1982) found that high oxygen availability in the bioftlter favored nitrifying bacteria over heterotrophic aerobes and starch hydrolyzers that compete for attachment sites.

This food-production system produces good yields of both fish and vegetables (McMurtry et al. 1990b) and reduces production costs relative to separated systems (Rakocy 1989b; McMurtry et al. 1990d) .

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Table 1. Physical parameters of tank to biofilter (treatment) ratios.
Biofilter ratio (v/v) Water: Biofilter (v/v) No. Plants (m-2) (plot1) Irrigation (liter m-2 d-1)
1: 0.67 1 : 0.67 4 500
1: 1.00 1 : 1.00 6 500
1: 1.50 1 : 1.50 9 500
1: 2.25 1 : 2.25 14 500


Table 2. Elemental composition of the fish feed input to the system
Element N P K Ca Mg Cl S Fe Mn Zn Cu B Mo
Fish Feed (%) 4.65 0.88 1.20 1.31 0.28 0.6 1600 201 52 65 12 22 0.4




Table 5. Fish growth during the 362 day interval with ‘Laura’ tomato, no crop, ‘Fidelio’ cucumber and ‘~cwalo’ tomato as influenced by tank to biofilter ratio.
Biofilter ratio (v/v) G (g d-1) Composite Growth Rates Composite Production Ratios
MSG (%) Fish increase (kg m-3) DRIB (%) Increase (%) Fruit yield / Fish increase (kg kg-1)
1: 0.67 1.80 148.4 1.08 23.77 0.96 3.8
1: 1.00 1.93 154.8 1.11 27.10 2.26 3.27
1: 1.50 2.07 162.2 1.18 27.38 1.52 4.51
1: 2.25 2.16 176.5 1.22 28.41 1.02 6.92
LSD (P=0.05) NS NS NS 3.12 0.28 1.32
G: average growth rate of individual fish during the culture period
MSG: average monthly specific growth rate
DRIB: daily rate of increase of the biomass calculated from Br= Bi (1 + i)n where n= interval in days and i = (DRIB/100)
NS: Non-significant


Table 6. Water quality and total amendments made during the 362 day interval of ‘Laura’ tomato, no crop, ‘Fidello’ cucumber and ‘Kewalo’ tomato as influenced by tank to biofilter ratio.
Biofilter Ratio (v/v) Water Temp (°C) NH3 (mg/l) NO2- (mg/l) NO3- (mg/l) pH HOH Added (liters) pH Adjustment (l m-2) Lime (g) CaO (g)
1: 0.67 28.7 4.49 0.65 229.0 5.94 3782 3815 2000 265
1: 1.00 28.7 3.82 0.53 237.0 5.75 4285 2857 2000 324
1: 1.50 28.1 2.88 0.46 207.0 5.83 5007 2225 2000 221
1: 2.25 27.7 1.87 0.32 92.0 5.97 7170 2125 2000 51
LSD (P= 0.05) 0.29 1.2 0.50 0.11 72.4 NS 406
165 NS 150

D0 : dissolved oxygen
TAN : total ammoniacal nitrogen
lime : CaMgCaMg(CO3)2
CaO : Calcium oxide
NS : Nonsignificant




Note; Figures 2 and 3 are yet to be added to this page…..