Note: Experimental Design has been revised. See Second Addendum to the Eighth Work Plan
Note: Schedule has been revised. See First Addendum to the Eighth Work Plan

Objective
Significance
Anticipated Benefits
Beneficiaries
Experimental Design
Sampling Schedule

Objective

Evaluate the effect of water exchange on pond dissolved oxygen and water quality.

Significance

Optimization of water use, a component of the production optimization research area, is the focus of this experiment. In addition, this experiment should increase our understanding of effects of various levels of water exchange on pond dynamics and nutrient concentrations of pond effluents. The previous experiment will have provided information on the impacts of daily water exchange. However, many producers base their water exchange program on daily pond DO, not a set daily rate. This experiment will build on the previous experiment by investigating the effects of water exchange on maintaining early morning dissolved oxygen above a minimal level.

Anticipated Benefits

Information from this experiment would continue to refine the techniques for exchanging water efficiently.

Beneficiaries

This information will be useful to shrimp producers who stock semi-intensively and exchange water to maintain DO levels.

Experimental Design

The exact design may change depending on results from the previous experiment.

Site: Private shrimp farms in Choluteca

Pond Facilities: 12 earthen ponds of about 1 ha on one farm and blocks of 3 ponds each on other collaborating farms.

Culture Period: warm season (rainy season), May - August; cool season (dry season) November - February

Stocking Rates: Post larvae will be stocked at 25/m². A survival rate of 30% will be assumed because of the Taura syndrome.

Water Management: per treatment

Test Species: Penaeus vannamei

Sampling Plan: A completely randomized design will be used to test 4 water exchange regimes.

1. 2% a day;

2. 5% only when early morning DO is 2.5 or less;

3. 10% only when early morning DO is 2.5 or less;

4. 15% only when early morning DO is 2.5 or less.

Each treatment will be replicated 3 times. Water exchange will be accomplished independently for each pond within each treatment. A complete experiment will be arranged on one farm, and other collaborating farms may simultaneously stock a block of 4 ponds, each one tested at one of the water exchange regimes. Shrimp in all treatments will be fed a complete ration with 20 - 25% protein at equal rates prescribed by the results of a current experiment. The experiment will be repeated during hot and cool growing periods. Dissolved nutrients, chlorophyll-a, BOD, and salinity will be determined weekly for all ponds. Dissolved oxygen, water temperature and pH will be monitored in the field.

Statistical Methods and Hypotheses: Data will be analyzed with ANOVA and orthogonal contrasts to test the hypothesis that volume of water exchange per exchange event does not affect early morning DO, pond water quality, or shrimp production.

Sampling Schedule

Cool season study: 11/97 to 2/98

Hot season study: 5/98 to 9/98 (if funding is extended)

Final Report Submittal: 4/98