Abstract
This work evaluated the effects of dietary supplementation of A-Live (phytogenic) either individually or in combination with Aquaform (potassium diformate, acidifier) on juvenile Nile tilapia (Oreochromis niloticus) growth performance, innate immune parameters, gut microbiome, and resistance against Francisella noatunensis subsp. orientalis challenge. Each experimental group contained 140 fishes (34.3 ± 0.33) in two 150L tanks. The experimental design consisted of five groups: a negative control; treated groups (G1, G2, G3) supplemented with different concentrations of A-Live and Aquaform in the feed; and a positive control (PC) for pathogen infection. Groups G1, G2, G3, and PC were challenged with Francisella spp. after 15 days. After infection, the mortality was significantly lower in groups G1, G2, and G3 (p < 0.01). Furthermore, these groups showed significant increase (p < 0.05) in daily weight gain, feed conversion rate, and specific growth rate. The PC group presented increase (p < 0.05) in the leukocytes and neutrophils number. Innate immunity parameters showed no difference between treatments after infection. Microbiome analysis revealed an increased number of bacteria belonging to the Vibrionaceae family after pathogen infection suggesting a secondary pathogen function of these bacteria. These results validate the beneficial effects of these products in tilapia farming.
Highlights
World aquaculture is the sector of animal production that has been showing the highest rate of growth in recent decades[1,2,3]
A smaller number of bacterial cells were visualized in the presence of A-Live than in Aquaform, suggesting that A-Live was capable of causing rapid damage to Francisella spp. (Supplementary Fig. 1)
In vivo results showed better feed conversion ratio (FCR) and specific growth rate (SGR) in groups G2 and G3, which received the combination of the two products at A-Live concentrations of 0.2% and Aquaform of 0.2% and at A-Live of 0.5% and Aquaform of 0.2%, respectively
Summary
World aquaculture is the sector of animal production that has been showing the highest rate of growth in recent decades[1,2,3]. Despite the high potential to increase production of aquatic organisms, there are still many barriers to the development of this sector in many countries[4,5,6]. This rapid growth has led producers to use intensive and super-intensive production systems that have positively increased productivity but have increased the disease susceptibility of fish[7]. Recent studies have reported that phytogenic compounds are capable of promoting improved performance, stimulating the innate immune response, and decreasing mortality against bacterial challenges in fish. Studies evaluating the effect of phytogenic compounds on growth, immunity, and resistance to diseases in Nile tilapia are rare
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