Novel bacterial meal may help promote robust immune response in shrimp

The study, which was published in Frontiers in Marine Science​, and led by Dr Orapint, Department of Aquaculture, Faculty of Fisheries, Kasetsart University, Bangkok, indicated that the methanotroph bacteria meal can entirely replace fishmeal in white shrimp diets.

At a 15% inclusion rate, FeedKind in shrimp diets, said the researchers, showed no adverse effects on growth performance, feed utilization and survival rate.

In addition, they noted shrimp in the study​​, which was funded by Calysta, demonstrated an increased tolerance to disease when challenged with V. parahaemolyticus​, the causative agent of Early Mortality Syndrome (EMS), indicating the bacteria meal protein may help promote a robust immune response.

EMS is one of the biggest issues facing shrimp farming today, having cost the industry billions of dollars since it was first identified in Asia in 2009.

The study ​

The growth trial comprised four treatments and five replicates of each:

• T1: A fishmeal-based control containing 15% fishmeal and three diets with graded levels of methanotroph bacteria meal.
• T2: 5% methanotroph bacteria meal
• T3: 10% methanotroph bacteria meal
• T4: 15% methanotroph bacteria meal.

The authors explained that shrimp were fed ad libitum​ for six weeks on trial diets to assess growth.

Subsequent to the growth trial, three replicates of the same groups were exposed to V. parahaemolyticus​ by a single bath challenge and held for a further 15 days on the same diets as the growth study to assess survival and resistance, said the researchers.

Results ​

No significant differences in survival or in growth performance, including final weight, weight gain, specific growth rate, feed consumption or FCR of white shrimp fed feeds containing the methanotroph bacteria meal or control diets for six weeks.

Immune markers such as hemocyte counts, phenoloxidase, superoxide dismutase and lysozyme activity were similar across all groups after the six-week feeding trial, noted the team.  

In the V. parahaemolyticus​ challenge, methanotroph bacteria meal in the diet significantly promoted the survival rate, and the reduction of Vibrio sp.​ in the hepatopancreas of white shrimp, they said.

“Hemocyte count and phenoloxidase activity showed no significant differences between diet treatment groups, but hemolymph protein was significantly higher in shrimp fed diets containing 15% methanotroph bacteria meal after challenge.” ​

The Vibrio​ colony counts from hepatopancreas in the treatment groups were all significantly lower than the control, added the authors.