Synbiotic Application for Pacific White Shrimp Litopenaeus vannamei: Resistance to Infectious Myonecrosis Virus and Growth

Abstract

Outbreaks of Infectious Myonecrosis (IMN) attack white shrimp farming in Indonesia and caused death up to 70%. Many studies have shown efficacy of probiotics in improving the resistance of shrimp or fish against disease by suppressing pathogens, while enhancing immunity and or improving water quality. Application prebiotics also has shown a variety of benefits to the aquatic animal. However, the combination of probiotics with prebiotics (synbiotics) showed better results than when it is applied separately. This study aimed to evaluate the potential of synbiotics from SKT-b bacteria and oligosaccharides-extracted from sweet potatoes, in increasing both white shrimp resistance to IMN and their growth performance. The experiment was conducted in Mei-September 2012, held at the Fish Health Laboratory, Faculty of Fisheries and Marine Sciences and the Diploma Programme, Bogor Agricultural University. This study includes the preparation of a prebiotic (sweet potato-extrac preparation and analyzes of oligosaccharides), preparation of probiotic bacteria (SKT-b bacteria growth), in vitro and in vivo tests. In vitro study tested the combination of prebiotics dose 0, 1, 2 and 3% and probiotics 107, 108, 109, 1010 cfu ml-1, that result the best growth of probiotic bacteria. In in vivo test, the white shrimp was given a feed in which probiotics (1010 cfu g feed-1) with various doses of prebiotics (0, 1, 2, and 3%) added, for 30 days. Measurement parameters to test the growth performance is conducted at the end of treatment, including specific growth rate, feed efficiency, retention of nutrients (protein and lipid) and the activity of digestive enzymes (protease and amylase). On challenge their resistance to IMN, shrimp was infected with IMN virus (IMNV) through injection and was observed for 10 days. Parameters observation includes survival, clinical symptoms, and immune parameters (total hemocyte [THC] and phenoloxidase [PO] activities). The ethanol extract of sweet potato used in this study contains three types of oligosaccharide-which are maltoheptaosa, sucrose, and raffinose-with the total concentration of oligosaccharides that reached 64,86%. SKT-b bacteria reached its optimal growth after 16 hours which was 5,9 x1010 cfu ml-1. The results of in vitro assays showed that the addition of prebiotic in culture medium can increase the growth of SKT-b bacteria which was positively correlated with the escalation of the dose of prebiotics and the concentrations of inoculants. The most optimal combination of prebiotics and probiotics was obtained from the addition of 3% of prebiotics and 1010 cfu ml-1 of SKT-b bacteria inoculant. In in vivo tests, the synbiotic feeding treatment (Pro+Pre) for 30 days increased shrimp survival and lowered its infection rates to IMNV, along with the increasing doses of prebiotics. This is because the increased of shrimp’s immunity after the synbiotics treatment was given. Pro+Pre 2% and Pro+Pre 3% treatment can increase THC of white shrimp to two times greater than THC of the shrimp control in the beginning of the observation. The decrease the amount of THC in both treatments after infection IMNV indicates a rapid reaction to the infection. IMNV infection caused the increase of PO activities in the shrimp in all treatments until the end of the observation. The highest PO activity itself occurred in Pro+Pre 3% treatment. The giving of synbiotic feed does not affect the growth rate. However, it can improve the food efficiency of shrimp with Pro+Pre 2% and Pro+Pre 3% treatment. This is caused by the increase of protease and amylase enzyme activities compared to the controls, which is believed can increase the digestibility of the feed. The retention value of protein and lipid in the shrimp with Pro+Pre 2% and Pro+Pre 3% treatment is also higher than the control, which indicates the better nutrient absorption. In general, Pro+Pre 2% and Pro+Pre 3% treatment showed a better response to both the increase of the resistance to IMNV infection and the growth performance of white shrimp.