Intensive production of the white leg shrimp, Litopenaeus vannamei (Boone 1931), in Central America and SE Asia is estimated to have reached more than 4.5 million t in 2019. Despite remarkable progress in shrimp nutrition and feed formulation, disease outbreaks in shrimp ponds can still lead to farming setbacks and increased use of antibiotics. Although state-of-the-art shrimp farm management is often practiced, severe losses have occurred, diagnosed as white feces disease (2010) and early mortality syndrome (EMS, aka acute hepatopancreatic necrosis syndrome AHPNS). EMS is a fatal disease occasionally found in farmed shrimp throughout the world, with an estimated global cost to the aquaculture industry of USD 1 billion. Both diseases are caused by Vibrio spp., a bacteria residing in the shrimp gut and hepatopancreas. In both cases, affected organs are ruptured, reducing feed intake and shrimp condition with massive mortalities within a few weeks after stocking. Researchers have meanwhile identified at least four strains of Early Mortality Syndrome (EMS) in shrimp farms in Latin America within the last few years. These were isolated either from the stomach of diseased shrimp or from the sediment of AHPNS-affected farms. Since dietary acidifiers are known particularly to inhibit pathogenic Gram-negative bacteria directly, they may therefore have a supporting action in suppressing the onset of the disease. This formed the impetus for a commercial trial in an affected area in Mexico, which tested the use of two different dietary acidifiers.
15 ponds on a commercial farm of approx. 6 ha each were stocked with 110,000 PL of white leg shrimp per ha. The farm had had previous issues with Vibrio spp., including Vibrio parahaemolyticus occurrence. While the control diet (containing 0.2% of an additive based mainly on citric acid, fumaric acid and phosphoric acid) was fed to shrimp in 11 ponds, the test diet in 4 ponds contained potassium diformate (KDF, 0.3%; Aquaform®, ADDCON). Shrimp were fed to satiation over the course of the day. The trial lasted for 123±8 days. Results on performance and productivity index are expressed as mean ± standard deviation. Data were subjected to statistical analysis and a significance level of 0.05 was used in all tests.
Results showed a significantly higher (P=0.03) number of harvested shrimp in the ponds fed with KDF (368,000 vs. 246,000). Therefore, the overall survival rate tended (P=0.09) to be increased in shrimp on diets containing dietary potassium diformate (54.6% vs. 39.7%). Shrimp in the KDF-fed ponds had a significantly (P= 0.02) lower final weight, but achieved a highly significantly (P<0.01) improved feed conversion (2.00 vs. 2.23). The harvested biomass per ha was numerically increased by almost 80 kg/ha when fed with KDF (900 kg vs. 822 kg). Overall, this led to an increased productivity index, based on weight gain, survival rate and FCR (P<0.1). by almost 30% (45.5 vs. 35.1) in shrimp fed with KDF.
Using dietary diformates therefore poses a promising nutritional alternative to reduce bacterial related losses in modern shrimp farming, even when tested against a positive control and contributes to an economically and ecologically sustainable grow-out operation.