5-Aminolaevulinic acid reduced the mortality of the Pacific white shrimp Litopenaeus vannamei infected with Enterocytozoon hepatopenaei

Abstract

Hepatopancreatic microsporidiosis, the shrimp disease caused by Enterocytozoon hepatopenaei (EHP) infection, has been widely spread in farmed Litopenaeus vannamei in Thailand. The symptoms include decreased feeding, muscle waste, slow growth, and chronic mortality. Since 5-aminolaevulinic acid (5-ALA), a non-protein amino acid, has been known to enhance ATP production in the cell through the increased formation of hemoproteins in the electron transport complex of mitochondria, it was hypothesized that providing 5-ALA to EHP-infected shrimp might reduce the mortality caused by the infection. Naturally EHP-infected L. vannamei were randomly sampled from a commercial shrimp pond that showed signs of hepatopancreatic microsporidiosis. The shrimp samples were reared under 30-ppt seawater in 40-L plastic tanks, divided into four groups; each receiving commercial pellets supplemented with different doses of 5-ALA: 0 (control), 15, 30, and 60 ppm. After 21 days of the experiment, it was found that the shrimp receiving 5-ALA at 60 ppm survived at a rate significantly (p < 0.05) higher than that of other groups, and had a significant increase in biomass, compared with that of the control group. Histology of the hepatopancreas of the 60-ppm group revealed significantly (p < 0.01) less percentage of atrophic tubules and larger areas of the vacuoles of the B-cells, suggesting improved hepatopancreatic functions. The levels of the EHP load in the hepatopancreas as revealed by semi-quantitative PCR were increasing in a dose-related manner of 5-ALA supplement. Histology of the hepatopancreas also revealed the presence of EHP. The ATP levels in the hepatopancreas of the 30- and 60-ppm groups were significantly (p < 0.01) higher than that of the control group. Further tests are required in commercial farms to find out if the 5-ALA supplement is beneficial to tackle the problem of hepatopancreatic microsporidiosis at the industrial level.