ROLE OF ALGAE EXTRACTS IN REDUCING STRESS AND ACUTE HEPATOPANCREATIC NECROSIS SYNDROME (AHPNS) MORTALITIES IN WHITELEG SHRIMP Litopenaeus vannamei

Algae are known for their biological activities. Many algae species were, and still are, used in the development of traditional medicine. The main active component of these algae are marine sulphated polysaccharide (MSP) molecules which are only found in marine plants. These MSP's have shown highly biological activity, including immunomodulatory, anti-bacterial, anti-viral, mucin-stimulating, anti-hyperlipidemic activities.

In an industry where intensive culture sets a high strain on the culture conditions, and where sustainability is becoming an important factor in production, natural solutions are what is needed. Stressful conditions can be found during transport from hatchery tanks to grow out ponds, changes from the hatchery environment to the more challenging grow out pond environment and throughout the intensive grow out systems. These factors are just a few that can create the right conditions for disease to develop. One such  disease that has had a large impact on the shrimp industry over the past 7 years is AHPNS. In many cases diminishing the total production by half. Even today the industry is looking for different ways to reduce the risks of AHPNS. Here too, preventive measures are often the best practices.

Olmix has specialized in using algae in innovative ways to increase sustainable production. The aim of this study was to see if these natural algae extracts would help improve shrimps ability to cope with stress and if they could improve the survival after an AHPNS disease challenge.

The trial was set up in two parts. The first part was aimed at stress tolerance of shrimp PL. PL 5 shrimp kept in 4 tanks until the size PL12. All tanks received the same standard diet. Treatment 1 was the control receiving only the standard diet. Treatments 2, 3 and 4 received the standard diet but coated with the algae extract during 3, 5 and 7 consecutive days respectively, prior to the different stress tests (10ppt salinity, 30ppt salinity and 100ppm formalin stress tests).

At PL 12 the shrimp were submitted to three different stress tests. Results showed that there was an increasing survival rate when algae was added to the diet prior to the stress tests. These results suggest that algal extracts help increase the PL tolerance of the stress tests of which they were submitted.

The second part was aimed at testing against a challenge test. In separate tanks PLs were raised to size PL25 when they were submitted to an immersion challenge with AHPNS infected bacteria (vibrio paraheamolyticus). Here too, after receiving similar treatments as in the stress tests (0, 3, 5 and 7 consecutive days of algae extract coated feed prior to the challenge test), the recorded mortalities show a dose dependent increased survival over the post challenge period.

In conclusion this study highlights the capacity of algal extracts to provide a natural way of reducing mortalities caused by stress and by an AHPNS challenge.