February 15-18, 2009 Washington State Convention Center Seattle ...

2 0
EFFECTS OF FISHMEAL VERSUS SOYBEAN-BASED FEEDS AND SOLIDS REMOVAL
BY SETTLING TANKS AND TILAPIA ON HIGH-DENSITY SHRIMP Litopenaeus vannamei
PRODUCTION IN BIOFLOC CULTURE SYSTEMS
Andrew J. Ray*, John W. Leffler, Gloria Seaborn, Beth Thomas, Jesus A. Venero, Luis Vinatea and Craig L. Browdy
SCDNR - Waddell Mariculture Center
211 Sawmill Creek Rd.
Bluffton, SC 29910 USA
raya@dnr.sc.gov
Biofloc-based culture systems function as an environmentally friendly, cost-effective method of growing shrimp (Litopenaeus
vannamei) at high density. The microbial communities, largely contained within biofloc particles, are responsible for nutrient
cycling, system stability, and growth-enhancement benefits for shrimp. Regulating the abundance and composition of these
microbes is an important step in maintaining reliably productive systems. In addition, the feeds used in biofloc systems should
be cost-effective, eco-friendly, and provide optimal nutrition for accelerated shrimp growth. We explored these requirements
by applying three biofloc solids management tactics along with two feed formulations in high-density culture units. System
dynamics and shrimp performance parameters were evaluated in light of these treatments.
Shrimp were stocked at 300/m 2 in 3.35m diameter, 6.3m 3 outdoor tanks. A high quality, soybean meal-based diet and a traditional,
fishmeal-based diet were each administered to half of the tanks. Among tanks receiving each diet, one third had solids
removal in the form of a settling chamber, one third had water diverted through a tilapia tank, and the remaining third received
no additional management. The combination of solids removal tactics and feed types created six unique treatments; each was
replicated four times. Differences in biofloc nutrition were measured with proximate analysis and fatty acid assessments.
System dynamics were assessed by measuring turbidity, total and volatile suspended solids, water quality parameters, percent
light penetration and community respiration. Microbial dynamics were monitored with light microscopy observations and fatty
acid biomarkers. Shrimp performance was characterized by mean individual weight, biomass yield, feed conversion ratio, and
survival. Shrimp quality was determined using a double-blind taste test and by testing product shelf-life.
The two diets led to differences in shrimp growth and feed conversion ratios. Differences in the nutritional profiles of biofloc
generated by the two diets were documented and these correlated with disparities in shrimp flesh nutrition and quality. Removal
of suspended solids by both the settling chambers and the tilapia increased light availability in tanks and reduced the
occurrence of potentially harmful cyanobacteria. Settling chambers reduced the abundance of bacteria and zooplankton while
tilapia reduced algae from systems. Both settling-based and tilapia-based solids removal increased system stability by reducing
oxygen demand and enhanced shrimp growth and survival compared to the non-cropped systems. This project demonstrates
that suspended solids management techniques provide benefits for shrimp production in high-density biofloc culture. The
study also shows that a carefully formulated plant-based diet can produce shrimp production results equivalent to those of a
traditional, fishmeal diet.