The threat of disease in the aquaculture industry, coupled with greater restrictions or ban on antibiotic use, has increased interest in evaluating antibiotic alternatives.
The most recent disease to hit the global shrimp industry is the acute hepatopancreatic necrosis disease (AHPND) or more commonly known as early mortality syndrome (EMS), where shrimp mortalities can be 100%.
Certain strains of Vibrio parahaemolyticus have been identified as the causative agents. In response, this has led to the abuse and overuse of antibiotics in the aquaculture industry.
The uncontrolled use of antibiotics can negatively affect the host species, the environment as well as the health of human consumers which has led to greater restrictions or ban of such practices in many countries
A promising alternative is organic acids, which have been used for decades in the livestock feed industry as an antimicrobial and growth promoter.
However, very limited information exists on their applications to the shrimp aquaculture industry.
The aim of the study was to examine the potential beneficial effects of a novel microencapsulated organic acid blend (OAB) to the production of tiger shrimp, Penaeus monodon.
The shrimp were raised in earthen ponds at a commercial farm and fed commercial feeds without (Diet A) or with (Diet B) organic acid supplementation at 2% OAB throughout the grow-out period.
Farm-raised shrimp were randomly sampled and transferred to the laboratory to examine any effects on nutrient utilization, resistance of shrimp to Vibrio harveyi and associated hepatopancreatic histopathology and phenoloxidase (PO) activity.
Results showed that after 22 weeks of culture in ponds, shrimp growth was similar between treatments. Lower nitrite-N and nitrate-N concentrations in the pond water indicated potential improved protein utilization from shrimp fed the organic acids.
This was supported by data from the digestibility trial, demonstrating crude protein, but also dry matter, ash and phosphorous utilization was significantly enhanced in the Diet B shrimp.
Total viable bacteria and presumptive Vibrio spp. counts were lower at the end of the grow-out period in the pond water of shrimp fed Diet B.
Shrimp fed Diet B showed significantly higher survival under V. harveyi challenge, likely due to enhanced PO activity and less hepatopancreatic damage. Total viable bacterial and Vibrio counts in the hepatopancreas of shrimp fed Diet B were significantly lower compared to Diet A.
This study provides the first reported data on the use of dietary organic acids in a commercial shrimp farm setting.
The enhancement of nutrient utilisation may reduce feeding costs and improve water quality while the higher resistance of shrimp to pathogenic bacteria such as Vibrio spp. may provide shrimp farmers with an effective method to mitigate disease outbreaks in the global shrimp aquaculture industry.
April 2015
