Crustacean immunity against pathogens and stress is largely dependent on non-specific immunity. To date, no evidence is present for long term specific immunity in crustaceans. Oral administration of β-glucan and vitamin C has been found to have a synergistic effect on inducing the beneficial nonspecific immune responses and enzyme activity in white leg shrimp (L. vannamei).
Euglena gracilis is a freshwater microalga that has been used as a candidate for bioremediation and produce value- added nutrients. Euglena can also be cultured under heterotrophic conditions, under these conditions it has been found to accumulate up to 90% of the cell mass with linear β-1,3 glucan.
The strain of Euglena gracilis used, accumulates β-glucan granules, which constitutes about 50% of its cell volume. More than 90% of Euglena β-glucan is composed of linear chains of glucose molecules linked through β-(1-3) glycosidic bonds. Purified algal β-glucan and the whole algae as feed supplements were found to be safe in genotoxicity tests carried out using bacterial reverse mutagenicity and mammalian micronucleus tests. They were also found to be safe in both long-term (90 days) and short- term oral toxicity tests at inclusion levels up to 5% of the diet. Safety was also proven with dermal and inhalation studies.
To evaluate the effect of β-1,3 glucan in a commercial set up, trial was conducted in two locations using earthen ponds. The combination of with dried Euglena gracilis cells and vitamin C was given at 5g per kg of feed, supplemented twice per day, once a week in treatment ponds and performance was compared with untreated ponds. The parameters recorded were feed intake (daily), water quality parameters (weekly)- ammonia, dissolved oxygen and nitrate. Average body weight was measured weekly by netting at three different locations in each pond
Trial I was conducted for a duration of 28 days. The mean body weight was 1.1g higher in the group supplemented with algal β-glucan and vitamin C than the control. Feed conversion ratio (FCR) for the control and treatment group during the four weeks of trial was 0.48 and 0.40, respectively. The return on investment (ROI) was found to be 1:72.
Trial II, which lasted for 10 weeks from DOC 16, had all the ponds affected by white gut disease towards the end of the study. The control and two treatment ponds were found to have FCR and survival of 2.09, 70% (control), 1.26, 100% (treatment 1) and 0.99, 110% (treatment 2), the ROI was found to be 1: 53 and 1: 93 in both treatment ponds.