Uptake of Natural Food and Supplemental Feed by Cultured Nile - - PowerPoint PPT Presentation

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Uptake of Natural Food and Supplemental Feed by Cultured Nile - - PowerPoint PPT Presentation

Oct 25, 2022 151 likes •332 views

Uptake of Natural Food and Supplemental Feed by Cultured Nile Tilapia, Oreochromis niloticus (L.), in Laguna de Bay, Philippines Hartmut Richter 1 Angelito Gonzal 2 Ulfert Focken 1 1 2 Klaus Becker 1 Laguna de Bay (Physical properties) ! 911km

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SLIDE 1

Uptake of Natural Food and Supplemental Feed by Cultured Nile Tilapia, Oreochromis niloticus (L.), in Laguna de Bay, Philippines

Hartmut Richter 1 Angelito Gonzal 2 Ulfert Focken 1 Klaus Becker 1

1 2

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SLIDE 2

Laguna de Bay (Physical properties)

! 911km2 but only 3m deep

  • n average

! 22 inflows but only one

  • utflow (Pasig River)

! Annual temperature 25- 31°C ! Dissolved oxygen high due to wind mixing ! Water normally turbid (Secchi depth <30cm) due to resuspension of silty lake sediment

Watershed boundary Pasig River Sampling site

  • f this study
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SLIDE 3

Laguna de Bay from the air

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SLIDE 4

Water normally very turbid…..

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SLIDE 5

…..due to erosion in the watershed

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SLIDE 6

Settlements confined to shoreline

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SLIDE 7

Culture setups regularly destroyed by typhoons every few years

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SLIDE 8

Aquaculture started in 1970 in large netpens (milkfish)…

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SLIDE 9

…and later included small cage culture (tilapia and chinese carps)

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Materials & Methods

! Five trials 1996-97, each on one fish cage ! Five fish sampled per hour over 24 hours (N=120) ! Stomach content composition quantified by visual estimation of slide coverage under microscope ! Daily rations calculated with fish feeding model MAXIMS (dry weight basis)

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SLIDE 11

Results (1) - Fish body data

Date

  • St. Lengths

(cm) Total Weights (g)

  • 19. March 1996

10.0 41.0

  • 16. May 1996

9.1 30.5

  • 17. July 1996

9.0 32.5

  • 26. September 1996

with feed (8% BME) no feed 8.4 8.6 25.1 25.3

  • 14. January 1997

with feed (excess) no feed 7.5 7.5 15.4 14.8

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Results (2) - Diet Composition Analysis

0.1 0.2 0.3 0.4 0.5 1.5 6 10 14 18 22

Time of Day (hours) Stomach fullness (% BME) Detritus

  • O. Algae

Ceratium

  • B. Anim.

Zoopl.

Overall average Data for July 1996

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Results (3) - Diet Composition

March 1996 May 1996 July 1996

Detritus Ceratium Microcystis Coscinodiscus Zooplankton/Benthos Supplemental feed

  • Sept. 1996

SF

  • Sept. 1996

NF

  • Jan. 1997

SF

  • Jan. 1997

NF

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SLIDE 14

Results (4) - consumption compared to maintenance & other localities

1 2 3 4 5

Mar 96 May 96 July 96 Sept 96 SF Jan 97 SF Jan 97 NF George Rudolf Awasa Daily Ration (Dry Matter, % BME)

Natural food Other sites Supplemental feed Maintenance

(Maintenance calculated from Richter et al., 2002, Aquacult. Int. 10: 1-9) SF: supplemental feed given, NF: no feed

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Conclusions

! Food quality is a major limiting factor for unsupplemented fish ! Large amounts of supplemental feed are wasted, probably contributing to detritus ! When algal bloom occurs, supplemental feed not necessary

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Recommendations

! If supplementation must continue: ! Investigate sources of detritus, cut down on input and revert to extensive aquaculture

  • cut feed losses (less feed in more

daily doses, use solid-bottomed cages)

  • investigate possibility of culturing more

profitable species

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SLIDE 17

Thank you!

(You may now wake up again!)

Full version of thesis can be downloaded at http://opus-ho.uni-stuttgart.de/hop/ volltexte/2003/35/index.html