Honduras Research

Objectives:
Evaluate the effect of time of initiation of water exchange on pond dissolved oxygen, water quality, and shrimp production.

Significance:
The previous experiment indicated that daily or emergency water exchange did not affect significantly shrimp production, but that water quality was better in ponds that received daily water exchange. However, differences in water quality generally did not become pronounced until the latter half of the 12-16 week production cycle. Producers may find unacceptable the risk associated with utilizing an emergency only water exchange policy. However, it appears that the current standard practice of initiating water exchange beginning the 4th week post-stocking is not the most efficient water exchange strategy. This experiment will build on the previous experiment by investigating the effects of time of initiation of water exchange on pond early morning dissolved oxygen, water quality, and shrimp production.

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:
Site: Private shrimp farm in Choluteca
Pond Facilities: 9 earthen ponds of about 1 ha.
Culture period: warm season (rainy season), August-October; cool season (dry season) December-March.
Stocking rates: Post larvae will be stocked at 15/m2 . A survival rate of 50% 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 3 water exchange regimes:

1. Daily water exchange at 10% of pond volume starting the 4th week post-stocking
2. Daily water exchange at 10% of pond volume starting the 7th week post-stocking
3. Daily water exchange at 10% of pond volume starting the 10th week post-stocking

Each treatment will be replicated 3 times. Water exchange will be accomplished independently for each pond within each treatment. Pond water will be discharged and then added to refill ponds. Shrimp in all treatments will be fed a complete ration with 20-39% protein at equal rates prescribed by the results of a current experiment; use of higher protein feed is at discretion of farm manager in response to shrimp growth. The experiment will be repeated during hot and cool growing periods. Water samples will be collected weekly from ponds and supply canal and analyzed for dissolved nutrients, chlorophyll a, BOD, and salinity. Pond and canal water sampling will begin as soon as pond filling is completed. Dissolved oxygen and water temperature will be monitored daily in the field. Samples of feed will be collected weekly, bagged, and labeled (date, source, feed, protein, production date or batch), and frozen until submitted for proximate analysis.
Statistical Methods and Hypotheses: Data will be analyzed with ANOVA and orthogonal contrasts to test the hypothesis that time of initiation of water exchange does not affect early morning DO, pond water quality, or shrimp production.

Sampling Schedule:
Cool Season Study: December 1998-March 1999
Hot Season Study: August 1998-October 1998