Effects of dietary supplementation of a multi-strain commercial probiotic on growth performance, feed conversion ratio, and survival rate in rainbow trout Oncorhynchus mykiss

Abstract

In aquaculture, inefficient feed utilization and disease infections are main causes of delayed growth and mortality which results in economic losses. Research has demonstrated that by modifying the fish’s gut microbiota, probiotic treatment can improve nutritional performance and reduce mortality. This study was organized to examine the effects of commercial multi-strain probiotic PRO-360 (Bacillus subtilis, Bacillus licheniformes, and Bacillus magaterium) on growth performance, feed conversion ratio, and survival rate of rainbow trout (Ohcorhynchus mykiss). For this, a total of 945 fish each weighing 29.65 ± 2.57 g were divided equally into 15 flow-through raceway tanks and fed experimental diets at rate of 5% body weight for 90 days. The first group (T1) was given a basal diet; the remaining four groups (T2, T3, T4, and T5) received a basal diet supplemented with PRO-360 (4% or 6% w/v) at two different concentrations (1.5 g/kg and 3 g/kg). While assessing the growth performance, feed utilization, and survival, after 90 days feeding on experimental diets, no significant improvement of weight gain, specific growth rate, feed conversion ratio, or survival rate were observed in the probiotic supplemented group. However, fish given 3 g/kg 6% PRO-360 had the lowest FCR, the highest weight gain and the specific growth rates, and all groups had 100% survival. These findings imply that rainbow trout growth, feed utilization, or survival are not impacted by PRO-360 supplementation in feed under typical rearing conditions.