FEEDING OF TILAPIA ON MICROBIAL FLOCS

Yoram AvnimelechTechnion, Israel Inst of Technology

Figure 1

Figure 2

Recycled protein

Data on feed protein utilization

� Conventional fish, shrimp ponds 20-25%� ASP Tilapia ponds (Avnimelech) 45%� ASP Shrimp ponds (McIntosh) 45%� Closed shrimp tanks (Velasco) 63%

� ASP shrimp ponds, 15N studyMichele Burford et al. 18-29% of total N consumption

Typical Biomass:Intensive shrimp ponds 1-2 kg/m2

Intensive fish ponds 10 – 50 kg/m2

Objectives

� Evaluate uptake of microbial flocs by fish.

� Follow utilization of microbial protein by fish

� Develop predictive tools

Pacific Aqua farmsImperial valley CA

Pond Characteristics

1313Aeration, hp/1000 sq.m

2030-35% protein in feed

620% Daily Water exchange

ASPConventional

Tanks: 800 l20 fish, 107 g each15N added, + 150 g starch To incorporate all TAN in microbial cells

2 Experimental phases:

� 1. No feed added for 6 days.Only food source – microbial flocs

2. Feed added (6 days in Pacific, 9 days in Dor, Israel)

Results: a. Floc volume

Results: Floc volume

0

5

10

15

20

25

30

35

40

45

-5 0 5 10 15Days from stocking

floc

volu

me,

ml

FV = 31 – 1.714 t, R2 = 0.686,

Floc Plug contained 1.4% dry solidsDaily uptake per fish = 1.15g

0

100

200

300

400

500

600

700

TSS,

mg/

l

1 3 6 9 12

Days

Changes of TSS, Total suspended solids with time-20 mg/l day in no fed phaseDaily uptake per fish, 0.954 g

0.020.040.060.080.0

100.0120.0140.0160.0180.0

0 2 4 6 8 10 12 14daysm

gC/l

Changes of suspended carbon with timeC = 168 – 6.61 t R2 = 0.986 Daily uptake by fish 0.59 g carbon

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0 2 4 6 8 10 12 14days

mgN

/l

Changes of suspended nitrogen N = 24.8 – 0.868 t R2 = 0.987 Daily uptake by fish = 0.039 g N

= 0.25 g protein

Daily decrease of TSS, floc volume, suspended carbon and nitrogen,

during the no – feed period.

1.0341.181.1540.954Daily uptake by fish as equivalent SS (g/fish)

23.526.924.320Equivalent dry SS change (mg/l)

0.87 mg/l6.61 mg/l1.74 ml/l20 mg/lDaily measured change

NitrogenCarbonFloc Volume

TSS

Bonus: 15N Results

15N enrichment (%) of suspended matter in the Pacific Aquafarm tanks.

y = -0.0465x + 1.5942R2 = 0.9728

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

0 2 4 6 8 10 12 14

Days

%15

N

15N enrichment (%) of suspended matter in the Dor tanks.

y = -0.048x + 1.65R2 = 0.9455

0.00.20.40.60.81.01.21.41.61.82.0

0.0 5.0 10.0 15.0 20.0 25.0

Days

15n

enri

chm

ent

%

What are the reasons for the decline of 15N enrichment?

� 1. Uptake of 15N enriched microbial protein.

� 2. Excretion of TAN originating in “old”, un-tagged fish protein

15N percentage in fish sampledin the Pacific Aquafarm experiment

15N, Fish, California

0.30

0.32

0.34

0.36

0.38

0.40

0.42

0.44

0.46

0 2 4 6 8 10 12 14Days

15N

enric

hmen

t,%

15N percentage in fish sampled in the Dor experiment

15 n enrichment, Fish, Dor

0.30

0.32

0.34

0.36

0.38

0.40

0.42

0.44

0.46

0.48

0.50

0 5 10 15 20 25

Days

15N

enric

hmen

t,%

Calculation of N uptake and excretion

� Assumptions:� Two processes:� 1. Uptake of suspended N (flocs, feed)� 2. Excretion of TAN� NH3 volatilization, denitrification, negligible.

∆15Nw (mg /l) = ∆ 15Nw (%) x Nt (mg /l)

and:Net Nt uptake (mg /l) =

= ∆ 15N (mg /1)/∆15Nw(%)

Net Nt Uptake in Pacific was found to be44.4 + 14.8 mg N/ fish * day for both non-fed and fed phases(From balance approach, N uptakeWas 39 mgN/fish * day

The difference between uptake and accumulation by fish

A certain fraction of N taken up is excreted.Nt accumulated= Nt up – Nt ex

In previous calculations, both those using material balances and those using 15N,

The net uptake (accumulation) were obtained.Using the 15 N technique, it is possible to

evaluate amount of excreted N.

Results

� During the no-feed period in Pacific expt.,� N uptake was 25 mg N/day * fish.� N excretion 4.4 mg N/day * fish, � i.e. excretion was 15% of uptake, � Compared to ~ 70% for whole pond

balances.� Is it since microbial protein is a better

diet?? More work is needed

Conclusions (1)

� 1. It was shown that microbial flocs are effectively utilized by tilapia. Consistent results were obtained using a number of independent measures: Floc volume, changes in time of TSS, C & N in the water and changes with time of 15N in water & fish.

Conclusion (2)

� 2. for a tilapia pond with ca 25 kg fish/m3 and floc volume of ~ 30 ml/m3, about 50% of feed and protein requirement were supplied by the microbial flocs.

� 3. Volumetric concentration of flocs (FV) is an easily obtained indicator of floc feeding potential. e.g., 5 ml/l FV is equivalent to 700 kg feed/ha.

Conclusion (3)

� 4. It seems that flocs harvesting is independent of feeding.

� 5. Floc harvesting probably follows:� Floc Harvesting = VFC * FS * K(fish)� Where VFC is floc volumetric

concentration, FS, properties of flocs (size, charge, adherence..) and K (fish), prperty of fish (species, size, etc)

Conclusion (4)

� 6. It is possible that microbial protein has a higher availability than feed protein.

� 7 This topic needs and deserves more research

� Thanks for your attention� agyoram@tx.technion.ac.il