Effects of dietary β-glucan on maternal immunity and fry quality of rainbow trout (Oncorhynchus mykiss)

• Effects of β-glucan on brood females and fry quality of rainbow trout were studied.
• β-Glucan increased immune competence of broodstock.
• β-Glucan had positive effects on the immunity of fry and disease resistance.

The effects of dietary β-glucan on fry quality of rainbow trout were studied. Two feeding trials were conducted with rainbow trout broodstock (trial 1) and fry (trial 2). The experimental diets contained 0 (control), 0.1% and 0.2% β-1,3/1,6 yeast glucan. In trial 1, 45 female rainbow trout were randomly divided into three experimental groups (15 fish per group) and were fed with one of the three experimental diets over three months prior to spawning. In trial 2, fry descending from the control fed broodstock were allocated to three different treatment groups: control fed (L1, considered as the control), 0.1% β-glucan fed (L2), and 0.2% β-glucan fed (L3). The fry from the 0.1% β-glucan fed mothers were divided into two dietary groups: control fed (L4) and 0.1% β-glucan fed (L5), and the fry from 0.2% β-glucan fed females were also allocated to two treatment groups: control fed (L6) and 0.2% β-glucan fed (L7). In trial 2, the fry were fed with one of the experimental diets for two months. Brood fish fed the diet with 0.2% β-glucan exhibited the highest white blood cell (WBC) value, ACH50 and lysozyme activity (P < 0.05). Total Ig and IgM levels were significantly higher (P < 0.05) in all β-glucan fed females compared to broodstock fed the control diet. The ACH50 level was also significantly (P < 0.05) higher in oocytes from females fed 0.2% β-glucan diet compared to those of other groups. No significant differences (P > 0.05) in survival rates (from fertilization to swim-up stages) were found among dietary treatments. In trial 2, dietary β-glucan resulted in better final weight, WG and SGR in groups L2, L3, L5 and L7. ACH50, lysozyme, total Ig and IgM levels were significantly higher in group L3 compared to the control (L1), and comparable with those in group L7. The challenge experiment with Yersinia ruckeri showed that relative percent survival (RPS) was highest in L3, L5 and L7. The results indicated that administration of 0.2% β-glucan to rainbow trout fry only instead of feeding both brood fish and fry could have the same positive effects in promoting the immunity of fry and resistance to Y. ruckeri.