Title : Earthworm vermicompost to enhance shrimp Litopenaeus vannamei growth and inhibit AHPND disease in an experimental culture
Abstract:
In Mexico, annual shrimp aquaculture production is increasing, thereby requiring more feed inputs and disease inhibitors. Among organic fertilizers, Eisenia foetida solid humus is considered a strong promoter of plankton growth, helping develop these aquatic organisms. On the other hand, the excessive use of antibiotics in aquaculture has negatively affected farmed species and reduced shrimp growth because bacteria have become more resistant to antibiotics. That’s why it is important to find environmental alternatives to reduce shrimp diseases.
The aim of this study was to evaluate the effects of different doses of solid earthworm vermicompost as growth promoters and AHPND inhibitors. Five treatments with three replicates with 120 shrimp larvae in 120L tanks with zero water exchange. The tanks were fertilized with initial doses: control, 0.00mg·L-1 solid Vermicompost [VC], 275, 550, 825, and 1100 mg/L-1 . The doses were thereafter reduced by half on day fifteen. The experiment lasted 45 days. Growth, Food Conversion Ratio and survival were measured.
After the growth experiment, mortality accumulation was evaluated for each treatment when shrimp were challenged against Vibrio parahaemolyticus in three-liter bowls with three replicates, with 10 shrimp of 1.5g each bowl.
Water quality parameters were not constant during the experiment and showed significant differences (P>0.05) between the oxygen and pH treatments. We found that shrimp reared with organic fertilizer had the best growth (Figure 1), and the lowest food conversion average. On the other hand, we have that treatment over 550mg/l of vermicompost was effective against V. parahaemolyticus. Less than three shrimps died in these treatments in a period of 72h, contrary to treatments with less than 550mg/l who had over 50% of the mortality in the first 18h of the challenge (Figure 2). Control had the highest mortality with 80% of the shrimp dead before the 24h trail.
Some studies suggest that vermicompost is an important food resource for juvenile shrimp (Chakrabarty, 2008). This organic fertilizer improves water quality and enhances phytoplankton production (Bwala and Omoregie, 2009; Chakrabarty et al., 2009). We find that vermicompost is a real option for shrimp growth and can lower production costs. It can also enhance shrimp survival and increase shrimp production when used in the first stages of shrimp, when they are more susceptible to diseases, but further investigation is needed to identify which bacterial consortium in the vermicompost acts as an inhibitor of AHPND.
