Abstract
A 30-day feeding experiment was conducted to investigate effects of dietary allicin on survival, growth, antioxidant capacity, innate immunity and expression of inflammatory and appetite related genes in large yellow croaker larvae. Four iso-nitrogenous (53% crude protein) and iso-lipidic (19% crude lipid) diets were formulated via supplementing graded levels of allicin (0.0 (the control), 0.005, 0.01, and 0.02% dry diet, respectively). Results showed that, among dietary treatments, larvae fed the diet with 0.005% allicin had the highest survival rate (SR) (P < 0.05), while larvae fed the diet with 0.01% allicin had the highest specific growth rate (SGR) (P < 0.05). Activities of α-amylase in both pancreatic (PS) and intestine segments (IS) of larvae fed the diet with 0.01% allicin were significantly lower than that in the control (P < 0.05). On the other hand, the supplementation of 0.01% allicin in diets significantly increased activities of alkaline phosphatase (AKP) and leucine aminopeptidase (LAP) in the intestinal brush border membrane (BBM) of larvae than the control (P < 0.05), indicating the promoting roles of allicin on fish larval intestinal development. Moreover, compared to the control, both the nitric oxide (NO) content and the activity of nitric oxide synthase (NOS) were significantly up-regulated in larvae fed the diet with 0.005% allicin, and catalase (CAT) were significantly upregulated in larvae fed the diet with 0.02% allicin (P < 0.05). Transcriptional levels of pro-inflammatory genes including cyclooxygenase-2 (cox-2), interleukin-1β (il-1β) and interleukin-6 (il-6) significantly decreased with increasing allicin, compared to the control. The expression of appetite genes including npy, ghrelin and leptin significantly increased with the prolonged fasting period, and dietary allicin supplementation significantly increased the transcriptional level of neuropeptide Y (npy) at 0.01%, while increased the transcriptional level of leptin in larvae at 0.02% dosages (P < 0.05). These results showed that the supplementation of 0.005% – 0.01% allicin in diets could improve the survival and growth of large yellow croaker larvae probably by promoting intestinal development, alleviating inflammation and enhancing appetite.
Highlights
In recent years, many natural products from plants, animals and microorganisms have been shown to possess potential medicinal value for their extensive physiological function (Yuan et al, 2016)
Specific growth rate (SGR) of larvae showed the similar trend and the specific growth rate of larvae fed the diet with 0.01% allicin (8.93% day−1) was significantly higher than the control (8.38% day−1) (P < 0.05)
Similar results were found in final body length (FBL) and final body weight (FBW) of fish larvae (Table 3)
Summary
Many natural products from plants, animals and microorganisms have been shown to possess potential medicinal value for their extensive physiological function (Yuan et al, 2016). Phytogenic compounds contain a variety of bioactive ingredients, of which the higher proportion of component determines their main biological characteristic (Santos et al, 2011; Chakraborty et al, 2014). Some active phytogenic compounds, such as thymol, carvacrol, limonene, cinnamaldehyde and eugenol from the plant thyme, oregano, citrus, cinnamon and clove respectively, have been noted to exert positive effects on nutrition and health of animals (Wallace et al, 2010; Chakraborty et al, 2014; Upadhaya and Kim, 2017; Sutili et al, 2018). Allicin is reported to improve the non-specific immunity and disease resistance of fish (Jeney and Jeney, 2002; Petrunov et al, 2007; Aly and Mohamed, 2010; Nya and Austin, 2011; Talpura and Ikhwanuddin, 2012)
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