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The present study was performed to investigate yellow catfish manganese (Mn) requirement with Mn dioxide nanoparticles (MnO2NPs) as Mn source, and to evaluate effects of dietary Mn on growth performance, Mn metabolism and kidney health. Using MnO2NPs as the Mn sources, six experimental diets were formulated with dietary Mn levels at 1.67, 4.35, 7.37, 13.63, 26.06 and 50.37 mg Mn/kg diet, respectively, and fed to yellow catfish for 8 weeks. Yellow catfish growth performance and feed intake were the highest in the group of 13.63 mg Mn/kg diet, and the lowest in the group of 1.67 mg Mn/kg diet; and the feed conversion rate showed opposite trend with growth performance. Dietary Mn addition increased Mn content in the whole body, kidney and serum. The mRNA abundances of dmt1, zip8and znt10increased with the increase of dietary Mn level. Yellow catfish fed high dietary MnO2NPs level had higher mRNA abundances of dynamin1, dynamin2, cav1, cltcand eps15. Dietary Mn excess damaged the kidney histology. Yellow catfish fed the 13.63 mg Mn/kg diet had higher T-AOC, T-SOD, Mn-SOD, CAT activities, and mRNA levels of sod1, sod2and cat(antioxidant response), but lower mRNA abundances of grp78, ire1, perkand atf4(endoplasmic reticulum stress), tnfα, il1βand il6(inflammatory response). The broken-line analysis of WG and the linear regression of whole-body Mn retention against dietary Mn levels showed that optimal Mn requirement was 12.57 mg Mn/kg diet and 8.33 mg Mn/kg diet, respectively, with MnO2NPs as Mn source. For the first time, we explored the effects of dietary MnO2nanoparticles on growth performance, Mn uptake and metabolism, antioxidant responses, endoplasmic reticulum stress and inflammatory responses of the kidney, and determined the optimal dietary Mn requirement of yellow catfish fed MnO2nanoparticles-added diet.

Three diets were formulated with dietary zinc (Zn) levels at 12.10 mg Zn/kg (L-Zn), 18.69 mg Zn/kg (M-Zn) and 120.82 mg Zn/kg (H-Zn) to explore effects of dietary Zn on growth, nutrient composition, muscle development, antioxidant and inflammatory responses in the muscle tissues of yellow catfish, one of the important economic fish in several Asian countries, including China. Zn content in M-Zn group could meet Zn requirement of yellow catfish. 270 juvenile yellow catfish (4.97 ± 0.01 g, mean ± S.E.M) were stocked in nine 300-L indoors tanks, 30 yellow catfish in each tank, and randomly provided with three diets for 10 weeks. Among three treatments, yellow catfish fed the middle Zn diets showed higher growth performance and condition factor but lower feed conversion rate than those fed the high Zn diets. Dietary Zn addition increased muscle Zn contents, but did not significantly influence feed intake, viscerosomatic and hepatosomatic index, survival, moisture, lipid, crude protein and ash contents in the muscle. Dietary Zn levels significantly influenced mRNA expression of several muscle development-related genes, such as mef2a, myod, myf5, myog, mef2d, pax7, mrf4, myhcand mstn. Middle dietary Zn levels increased antioxidant capability and reduced oxidative stress, as evaluated by enzymatic activities, gene and protein expression related to antioxidant response. Fish fed the middle Zn diets had the lower il8, tnf-αand tnf-βmRNA expression but higher il10and tgf-βmRNA expression than those fed the high Zn diet, suggesting that optimal dietary Zn levels activated anti-inflammatory response and inhibited pro-inflammatory responses. Based on the observation, our study suggested that the suitable dietary Zn levels promoted the growth, muscle development, antioxidant and anti-inflammatory responses in fish.

Excessive phosphorus (Pi) contributes to eutrophication in an aquatic environment, which threatens human and fish health. However, the mechanisms by which Pi overload influences aquatic animals remain largely unexplored. In the present study, Pi supplementation increased the Pi content, inhibited lipid accumulation and lipogenesis, and stimulated lipolysis in the liver. Pi supplementation increased the phosphorylation of glycogen synthase kinase-3 β (GSK3β) at serine 9 (S9) but inhibited the phosphorylation of GSK3α at tyrosine 279 (Y279), GSK3β at tyrosine 216 (Y216), and peroxisome proliferator-activated receptor α (PPARα) at serine 84 (S84) and threonine 265 (T265). Pi supplementation also upregulated PPARα protein expression and stimulated its transcriptional activity, thereby inducing lipolysis. Pi suppressed GSK3β activity and prevented GSK3β, but not GSK3α, from interacting with PPARα, which in turn alleviated PPARα phosphorylation. GSK3β-induced phosphorylation of PPARα was dependent on GSK3β S9 dephosphorylation rather than Y216 phosphorylation. Mechanistically, underphosphorylation of PPARα mediated Pi-induced lipid degradation through transcriptionally activating adipose triglyceride lipase (atgl) and very long-chain-specific acyl-CoA dehydrogenase (acadvl). Collectively, our findings uncovered a new mechanism by which Pi facilitates lipolysis viathe GSK3β–PPARα pathway and highlighted the importance of S84 and T265 phosphorylation in PPARα action.

An experiment was conducted to determine the effect of dietary lipid levels on growth performance and body composition of grouper Epinephelus coioidesjuveniles cultured in floating netcages (1.5 m × 1 m × 1.5 m). Six isonitrogenous diets (53% dietary protein) with increasing dietary lipid concentration (5.16, 7.38, 9.73, 12.36, 14.13, 16.04% of dry material, DM) were fed to satiation to triplicate groups of 20 fish (mean weight: 10.9 ± 0.1 g) for 56 days. Dietary energy levels were 300, 322, 340, 371, 382, 400 kcal/100 g DM, respectively. Fish fed the 9L diet had the highest weight gain (WG) and specific growth rate (SGR), but they were not significantly different from that of fish fed the 7L or 12L diet (p> 0.05). FI varied inversely with dietary lipid levels. The poorest FCR and the lowest PER were observed in fish fed the 5L diet but these parameters showed no significant differences (p> 0.05) for fish fed the dietary lipid level ranging from 9 to 16%. Nitrogen intake decreased with dietary lipid levels. Fish fed the 7L diet showed the highest N gain, which was not markedly different from that of fish fed the 9L and 12L diets (p> 0.05). N retention was significantly lower in fish fed the 5L diet than in the other groups. Lipid intake and lipid gain increased with dietary lipid levels. Lipid retention (%) of the 7L diet was lowest but showed no significant differences among other treatments (p> 0.05). Proximate composition of fish body was significantly affected by dietary lipid level (p< 0.05). Body lipid content increased in direct proportion to dietary lipid levels. In contrast, moisture content of whole-body was correlated negatively to dietary lipid level. Dietary lipid content had no significant effect on protein content in whole-body and white muscle (p> 0.05). Condition factor (CF), hepatosomatic index (HSI) and viscerosomatic index (VSI) increased with increasing dietary lipid level. Based on second-order polynomial regression analysis of WG against dietary lipid level, a breakpoint of 10.0% was indicated to be the optimal dietary lipid concentration for maximum growth for grouper Epinephelus coioidesjuveniles cultured in floating netcages.