Abstract
The present study investigated the potential mechanisms of astaxanthin in the regulation of gastrointestinal immunity and retinal mitochondrial function of golden pompano (Trachinotus ovatus). Triplicate groups of juvenile T. ovatus (mean initial weight: 6.03 ± 0.01 g) were fed one of six diets (D1, D2, D3, D4, D5, and D6) for 8 weeks, with each diet containing various concentrations of astaxanthin (0, 0.0005, 0.001, 0.005, 0.01, or 0.1%, respectively). Growth performance of fish fed the D2–D5 diets was higher than that of fish fed the D1 diet; however, growth performance and survival of fish deteriorated sharply in fish fed the D6 diet. Gut villus in fish fed the D2–D5 diets were significantly longer and wider than that of fish fed the D6 diet. Feeding with D2–D5 diets led to increased abundance of Bacillus, Pseudomonas, Oceanobacillus, Lactococcus, Halomonas, Lactobacillus, and Psychrobacter while abundance of Vibrio and Bacterium decreased. Additionally, feeding with the D6 diet resulted in a sharp decline in Pseudomonas and Lactobacillus abundance and a sharp increase in Vibrio abundance. A low dissolved oxygen environment (DO, 1.08 mg/L) was conducted for 10 h after the rearing trial. No fish mortality was observed for any of the diet treatments. Lysozyme (LZY) activity in fish fed the D6 diet decreased sharply and was significantly lower than that in other groups. ROS production also decreased sharply in fish fed the D6 diet. Moreover, the conjunctiva and sclera in the fish fed the D6 diet were indistinguishable. Suitable dietary astaxanthin supplementation levels (0.005–0.1%) exerting a neuroprotective effect from low dissolved oxygen environments is due to up-regulated expression of anti-apoptotic factors, such as phosphorylated Bcl-2-associated death promoter (pBAD), phosphorylated glycogen synthase kinase-3β (pGSK-3β), Bcl-2 extra large (Bcl-xL), and down-regulated expression of Bcl-2-associated X protein (Bax) pro-apoptotic factor in retinas. Furthermore, suitable dietary astaxanthin levels (0.0005–0.01%) suppressed up-regulation of critical mitochondrial components, such as peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), mitochondrial transcription factor A (TFAM), and mitochondrial DNA (mtDNA), while excessive astaxanthin supplementation produces the opposite effect. In brief, high-dose astaxanthin arouses and aggravates low dissolved oxygen-induced inflammation, oxidative stress, intestinal disorder, retinal apoptosis, and retinal mitochondrial dysfunction in T. ovatus. Second-degree polynomial regression of WG indicated that the optimum dietary astaxanthin for juvenile T. ovatus is 0.049%.
Highlights
Aquaculture is the fastest-growing source of food production worldwide due to increased demand and decline of wild capture fisheries
When the quadratic regression analysis was used for estimating the optimum dietary astaxanthin for maximal growth of juvenile T. ovatus, the regression equations used was y = 146,507x2 + 14,486x + 1218.3 (Figure 1)
The present results showed that suitable astaxanthin diet treatments alleviate cell apoptosis in the retinas under hypoxic conditions, accompanied by up-regulation of retinal anti-apoptotic factors (BAD, GSK-3β, and Bcl-2 extra large (Bcl-xL)) and downregulation of retinal pro-apoptotic factors (Bax)
Summary
Aquaculture is the fastest-growing source of food production worldwide due to increased demand and decline of wild capture fisheries. Many species of marine fish lose their natural skin coloration under captive conditions compared to the wild conditions. Carotenoids have been shown to promote growth performance and reproduction, improve antioxidant activity and immunity, and positively benefit intermediary metabolism and coloring of aquatic animals (Chuchird et al, 2015; Rahman et al, 2016; Song et al, 2017). Astaxanthin (3,3 -dihydroxy-β, β-carotene-4,4 dione) has stronger antioxidant activity than canthaxanthin and β-carotene, which are found in many microorganisms, marine animals (such as shrimp), microalgae, and yeast (Chatzifotis et al, 2005; Niu et al, 2012, 2014). Astaxanthin has few concerning adverse effects compared to antibiotic use and is generally considered safe in the aquafeed industry (Shimidzu et al, 1996)
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