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Abstract: This study was aimed to examine the effect of dietary glycoprotein extracted from the sea mustard Hizikia fusiformis (Phaeophyceae: Sargassaceae) as a dietary supplement on growth performance in association with somatotropin level, proximate compositions, and immunity in juvenile olive flounder Paralichthys olivaceus. Water–ethanol extracted glycoprotein from H. fusiformis was supplemented to three fishmeal-based diets at the concentration of 0, 5, and 10gkg−1 diet (designated as H0, H5, and H10, respectively). After a 12week-long feeding trial, growth performance and biochemical responses were analyzed including proximate composition, and whole body amino acids and fatty acids. We also measured plasma insulin like growth factor (IGF), IGF-binding protein (IGFBP) and interleukin (IL). The fish fed H5 showed the greatest weight gain among the dietary treatments. In parallel with the growth, the fish fed the diets containing H. fusiformis glycoprotein showed an increased plasma IGF-I activity and increased expression of 43-kDa IGFBP-3 compared to that in the control, whereas an opposite trend was observed for 34-kDa IGFBP-1. Although no differences were found in the level of whole body linoleic acid (C18:2n−6) and linolenic acid (C18:3n−3) among treatments, increases in arachidonic acid (ARA, C20:4n−6), eicosapentaenoic acid (EPA, C20:5n−3) and docosahexaenoic acid (DHA, C22:6n−3) were observed in fish fed H5 compared to control. IL-2 and -6 levels increased significantly in fish fed H10 compared to those in the control indicating increased immunity. These results suggest that supplementation of H. fusiformis glycoprotein in fish diet may be beneficial for fish growth and immunity in juvenile olive flounder. [Copyright &y& Elsevier]

This experiment was conducted to compare l-ascorbyl-2-monophosphate-Ca (AMP-Ca) with l-ascorbyl-2-monophosphate-Na/Ca (AMP-Na/Ca) for supplying the dietary vitamin C for juvenile Korean rockfish (Sebastes schlegeli). Fish were fed 1 of 11 semi-purified diets containing equivalent of 0, 50, 100, 200, 400, and 800 mg ascorbic acid (AA)/kg diet in the form of AMP-Ca or AMP-Na/Ca for 12 weeks. After 12 weeks of the feeding trial, weight gain (WG), feed efficiency (FE) of fish fed with the control diet (vitamin C-deficient diet) were significantly lower than those of fish fed with the vitamin C-supplemented diets in either form (P<0.05). WG of fish fed with AMP-Na/Ca 400, AMP-Na/Ca 800, AMP-Ca 400 and AMP-Ca 800 diets were significantly higher than those of fish fed with the control diet, AMP-Na/Ca 50, AMP-Ca 50 and AMP-Ca 100 diets (P<0.05). In general, there was no significant difference between AMP-Ca diets and AMP-Na/Ca diets at the same supplementation levels. By the end of the 9th week, fish fed with the control diet began to show the initial vitamin C deficiency signs such as anorexia, erratic swimming behavior, darkening in skin color and reduced growth.The ascorbic acid concentrations in fish muscle and liver increased with the increase of the vitamin C supplementation levels in fish diets regardless of which kind of vitamin C source used. There were no significant differences in ascorbic acid concentrations in liver and muscle of fish between the two vitamin C sources at the same supplementation level.These results indicate that AMP-Ca is a bioavailable form of vitamin C source for Korean rockfish and it has the antiscorbutic activity equal to AMP-Na/Ca.Broken-line analysis of weight gain indicated that the dietary vitamin C requirement of Korean rockfish was 106 mg AA/kg diet based on the pooled WG of fish fed with the AMP-Na/Ca and AMP-Ca diets. However, based on the different forms of ascorbic acid, the vitamin C requirements were 101 and 112 mg AA/kg diet with the forms of AMP-Na/Ca and AMP-Ca, respectively. [Copyright &y& Elsevier]

An 11-week feeding trial was conducted to study the effects of the different levels of dietary vitamin C on growth, tissue ascorbic acid concentrations and histopathological changes in parrot fish. Casein and gelatin-based diets were formulated to contain 0, 60, 120, 240, 480 and 2000 mg l-ascorbic acid (AA) per kg diets on AA equivalent basis in the form of l-ascorbyl-2-monophosphate (AMP), 60 and 240 mg AA per kg diet as l-ascorbic acid. However, the analyzed AA levels were 0, 50, 100, 205, 426 and 1869 mg AA per kg diet in AMP supplemented diets; 36 and 149 mg AA per kg diet in l-ascorbic acid supplemented diets. Thus, the diets were designated as AA-free, AMP50, AMP100, AMP205, AMP426, AMP1869, AA36 and AA149. Fish averaging 3.9±0.06 g (mean±S.D.) randomly were fed the experimental diets in triplicate groups for 11 weeks. Weight gain (WG) of fish fed AMP50 and AA36 diets were significantly lower than those of the other groups, and fish fed AMP1869 diet showed a higher WG than did fish fed AMP50, AMP100, AMP205, AA36 and AA149 diets (P<0.05). However, there was no significant difference in WG between fish fed diets AMP426 and AMP1869, and among fish fed AMP100, AMP205, AMP426 and AA149 diets. Fish fed the AA-free diet began to show deficiency signs, such as retarded growth, darkening, anorexia and high mortality, after 3 weeks of feeding trial. After 6 weeks of the feeding trial, liver from fish fed the AA-free diet showed severe atrophy. By the end of the seventh week, all fish fed the AA-free diet were dead. Liver AA concentration from fish fed AMP50 diet was significantly lower than that from fish fed AMP205, AMP426, AMP1869 and AA149 diets, and fish fed AMP50, AMP100, AA36 diets showed a significant lower AA concentration in liver than did fish fed AMP205, AMP426 and AMP1869 diets.Broken line analysis of weight gain indicated that the dietary vitamin C requirement of parrot fish is 118±12 mg AA per kg diet in the form of l-ascorbyl-2-monophosphate for maximum growth. [Copyright &y& Elsevier]

Mercury isotope ratios in fish tissues have been used to infer sources and biogeochemical processes of mercury in aquatic ecosystems. More experimental studies are however needed to understand the internal dynamics of mercury isotopes and to further assess the feasibility of using fish mercury isotope ratios as a monitoring tool. We exposed Olive flounder (Paralichthys olivaceus) to food pellets spiked with varying concentrations (400, 1600 ng/g) of methylmercury (MeHg) and inorganic mercury (IHg) for 10 weeks. Total mercury (THg), MeHg concentrations, and mercury isotope ratios (δ202Hg, Δ199Hg, Δ200Hg) were measured in the muscle, liver, kidney, and intestine of fish. Fish fed mercury unamended food pellets and MeHg amended food pellets showed absence of internal δ202Hg and Δ199Hg fractionation in all tissue type. For fish fed IHg food pellets, the δ202Hg and Δ199Hg values of intestine equilibrated to those of the IHg food pellets. Kidney, muscle, and liver exhibited varying degrees of isotopic mixing toward the IHg food pellets, consistent with the degree of IHg bioaccumulation. Liver showed additional positive δ202Hg shifts (∼0.63‰) from the binary mixing line between the unamended food pellets and IHg food pellets, which we attribute to redistribution or biliary excretion of liver IHg with a lower δ202Hg to other tissues. Significant δ202Hg fractionation in the liver and incomplete isotopic equilibration in the muscle indicate that these tissues may not be suitable for source monitoring at sites heavily polluted by IHg. Instead, fish intestine appears to be a more suitable proxy for identifying IHg sources. The results from our study are essential for determining the appropriate fish tissues for monitoring environmental sources of IHg and MeHg. Image 1 • Marine fish was exposed to food pellets amended with inorganic and methylmercury. • All fish tissues equilibrated isotopically to dietary methylmercury. • Only fish intestine equilibrated isotopically to dietary inorganic mercury (IHg). • Redistribution or biliary excretion of IHg explains liver isotope fractionation. Mercury isotope fractionation in fish liver suggests liver cannot be used as a conservative proxy for IHg pollution. Fish intestine is a better proxy for tracing IHg sources. [ABSTRACT FROM AUTHOR]

Poly-γ-glutamic acid (γ-PGA) is an unusual anionic homopolyamide that is biodegradable, edible, and nontoxic. It has a wide variety of industrial applications depending on its combined cations, and molecular weight. In this study, extracellular viscous γ-PGA produced by halotolerant Bacillus sp. SJ-10 isolated from a traditional Korean salted-fermented seafood was purified and characterized. The physicochemical analysis indicated that the γ-PGA produced by Bacillus sp. SJ-10 consists primarily of d -glutamic acid residues combined with sodium cations. When batch fermentation was performed with 8% NaCl for 3 d, Bacillus sp. SJ-10 produced approximately 24.7 g/L γ-PGA with a molecular weight of approximately 400 kilodaltons (kDa). Under fermentation conditions with 6% NaCl, the maximum yield was 26.2 g/L regardless of the molecular weight. The γ-PGA sodium salt with a molecular weight of 400 kDa exhibited antioxidant activity by scavenging 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) radicals and reducing molybdenum, with maximal scavenging activity at 0.5 mg/mL and reducing activity at 1 mg/mL (20 μg ascorbic acid-equivalent), respectively. These results suggest the potential use of γ-PGA in the food, cosmetic, and biomedical industries for its antioxidant qualities. Our results also provide an economical method for controlling the molecular weight of the γ-PGA produced. [ABSTRACT FROM AUTHOR]

Abstract: This study was conducted to investigate the influence of dietary lipid level and supplemental soy lecithin on growth, feed utilization and body composition of juvenile flounder reared at two suboptimal water temperatures, 12 and 17 °C. Three isonitrogenous (CP 50%) diets containing 1% squid liver oil (S7), 7% squid liver oil (S14), and a mixture of 2% soy lecithin and 5% squid liver oil (SL14) were formulated to obtain 7% and 14% of crude lipid. Triplicate groups of fish (6.3±0.2 g) were fed to apparent satiation twice a day for 60 days. Weight gain, daily feed intake, feed efficiency and protein efficiency ratio were significantly higher for fish reared at 17 °C than at 12 °C. Daily feed intake was significantly decreased with the increase of dietary lipid level at the same water temperature, but weight gain was not affected by dietary lipid composition. At 12 °C, feed efficiency and protein efficiency ratio were significantly higher for fish fed the S14 and SL14 diets than those of fish fed the S7 diet, while at 17 °C feed efficiency and protein efficiency ratio of fish fed the S14 diet, which were not significantly different from those of fish fed the SL14 diet, were significantly higher than those of fish fed the S7 diet. There were no significant effects of dietary lipid composition or temperature range on the whole body contents of moisture, crude protein, lipid or ash. Dietary lipid composition and temperature affected the fatty acid content of the polar lipid from the liver; and the n-3HUFA contents such as 20:5n-3 and 20:6n-3 were higher at 12 °C than at 17 °C. The results of this study indicate that an increase of dietary lipid level from 7% to 14% has beneficial effects on feed utilization of flounder when reared in suboptimal water temperatures. The increase of water temperature from 12 to 17 °C improved growth and feed utilization, but 2% soy lecithin had no substantial effect on growth and feed efficiency of juvenile flounder. [Copyright &y& Elsevier]

(1,3)(1,4)-β- d -glucan has been determined to have various beneficial effects due to its unique structure. β-glucooligosaccharides (β-GOS), which are hydrolysates of barley (1,3)(1,4)-β- d -glucan, provide a useful prebiotic material for selective growth of probiotic bacteria. In this study, recombinant β-1,3-1,4-glucanase (Bg1314) from Bacillus sp. SJ-10 (KCCM 90078) was immobilized on porous silica using glutaraldehyde as a crosslinking reagent to achieve efficient production of β-GOS. We investigated the effects of factors such as the amounts of enzyme and glutaraldehyde, reaction temperature, and pH on catalytic activity. Enzyme activity decreased sharply at high concentrations of glutaraldehyde, likely due to the reaction of glutaraldehyde with lysine residues at the catalytic site of Bg1314, because lysine-substituted Bg1314 retained its activity under the same conditions. Immobilized Bg1314 protein (ImBg1314) was stable over a wide range of pH and could be stored long term at 4 °C. The optimal conditions of ImBg1314 were similar to those of Bg1314. However, the optimal temperature of ImBg1314 differed from that of Bg1314. The products were β-GOS composed of 3- O -β-cellobiosyl- d -glucose and 3- O -β-cellotriosyl- d -glucose. After ImBg1314 was reused for 10 cycles, it retained 42% of its initial catalytic activity. This study showed that the Imbg1314 applied economical production of β-GOS. [ABSTRACT FROM AUTHOR]

Extrusion technology is known to enhance feed quality by controlling feed processing conditions. Although extrusion technology has been extensively used to improve livestock feed quality, research on its effects on quality in fish is lacking. Furthermore, studies on feed processing, the physical properties of feed produced using extruders, and the effects of extrusion on formulated feed quality remain scarce. Therefore, in this study, we investigated the effects of extrusion pressure and raw material particle size on the growth performance and digestive physiology of rockfish (Sebastes schlegeli). Experimental diets were prepared under different extrusion pressures by manipulating the screw speed [low pressure (LP), 1080 rpm/min; high pressure (HP), 620 rpm/min] and mean raw material particle sizes [small size (SS), 199.1 μm3; large size (LS), 1026.8 μm3] in a two-level factorial design. Four experimental diets (SS/LP, SS/HP, LS/LP, and LS/HP) were randomly assigned to 12 tanks (3 replicates), which were each stocked with 30 fish (initial mean body weight, 82.7 ± 0.2 g). After a 16-week feeding trial, observations showed that SS and LP enhanced fish weight gain and plasma growth-related hormone activity. In addition, SS and LP increased intestinal digestive activity in fish, positively affecting growth. These results indicate that manipulating physical pellet qualities by adjusting the feed ingredient extrusion pressure and raw material particle size can improve the growth performance and digestive physiology of rockfish, which should be considered in feed manufacturing. • Extrusion pressure and particle size improved rockfish growth rate and growth hormone activity. • Higher water absorption ability of feed was associated with better fish growth. • SS and LP enhanced fish weight gain and plasma growth-related hormone activity. • SS and LP increased the digestive activity of the intestines. [ABSTRACT FROM AUTHOR]

The aim of this study was to improve the stability of β-1,3-1,4-glucanase by substituting hydrophobic residue for specific amino acid. The results indicated that the catalytic efficiency, thermostability and halostability were enhanced simultaneously by replacement of Lys48 with Ala (K48A) or Leu (K48L). Comparison of kinetic parameters revealed that catalytic efficiency of mutants is enhanced as a result of the increase in substrate affinity. A great improvement in thermostability and halostability was observed. The half-lives of mutants significantly increased (up to ∼7-fold) at 60–70 °C. Moreover, relative enzymatic activities of mutants were observed more than 80% even in the presence of 30% NaCl, and half-lives were increased to 3-fold that of wild-type. Based on above results, when applied to ionic liquid, mutants were more active and stable compared to wild-type. These were the results from improvement of protein functions by the substitution of hydrophobic single residue in adjacent with forming carbohydrate binding cavity. Therefore, this report could be helpful for improvement of the enzyme property and for biotechnological application as well. [ABSTRACT FROM AUTHOR]

This study was conducted to evaluate dietary myo -inositol (MI) requirement of juvenile parrot fish. A basal experimental diet was formulated and used as a control and four other diets were prepared by supplementing 100, 200, 400 or 800 mg MI per kg − 1 diet (designated as M0, M100, M200, M400 and M800, respectively). Triplicate groups of fish (initial body weight, 11.5 ± 0.01 g) were fed one of the diets to apparent satiation twice daily for 18 weeks. The results showed the significant increase of growth performance at dietary MI level of 100 mg kg − 1 but no further improvement was observed at higher MI levels. Significantly lower feed conversion ratio was obtained in fish fed the M200 and M400 diets than those fed M0 diet. Significantly lower AST and ALT activities were recorded in fish fed 100 and 100–800 mg kg − 1 MI, respectively, compared to those fed the control. Whole-body protein content decreased significantly at all supplementation levels of MI in comparison to control. Liver MI concentration significantly increased by MI supplementation and inversely correlated with liver lipid content. Broken-line regression analysis indicated that MI requirement of parrot fish is 94.3 and 121.3 mg kg − 1 diet based on weight gain and liver MI concentration, respectively. The findings suggest that approximately 100 mg kg − 1 MI can support maximum growth of juvenile parrot fish and prevent a potential abnormal lipid metabolism. [ABSTRACT FROM AUTHOR]

Abstract: Two consecutive feeding trials were conducted to investigate taurine essentiality and requirement for parrot fish (Experiment I) and to determine whether taurine supplementation to high soybean meal (SM) diets would improve its growth performance (Experiment II). In Exp I, a fish meal (FM) based diet was used as a control and supplemented with 0.2, 0.4, 0.8, 1.2 or 1.6% taurine, and fed to triplicate groups of juvenile parrot fish (initial body weight, 13.5g) to apparent satiation for 8weeks. The growth and feed utilization were significantly improved by taurine supplementation up to 0.8% and thereafter plateaued. An optimum dietary taurine level was determined by a broken-line regression analysis based on weight gain and estimated at 0.88% diet. In Exp II, six experimental diets were prepared by supplementation of 0 or 1.0% taurine to a FM-based diet or addition of 0, 0.1% (low), 1.0% (medium) or 2.0% (high) taurine to a basal diet in which 30% of FM was replaced with SM (designated as FM, FM+T1, SM, SM+T0.1, SM+T1 and SM+T2, respectively). Each experimental diet was fed to juvenile parrot fish (initial body weight, 6.4g) twice daily to apparent satiation for 12weeks. The fish fed SM diet showed significantly lower growth performance compared to fish fed FM-based diets. Supplementation of taurine to SM diet significantly affected fish growth and higher performances were observed in fish fed SM+T1 or SM+T2 diets that were comparable to that of the fish fed FM diet. However, no significant changes were observed regarding the inclusion of taurine into FM-based diet. These results clearly demonstrated the positive effects of dietary taurine supplementation on feed utilization and growth performance of juvenile parrot fish when 30% FM was replaced with SM. The optimum dietary level of taurine seems to be approximately 1% in diets. [Copyright &y& Elsevier]

Abstract: Two studies were conducted to investigate the effects of dietary supplementation of three Bacillus spp. on growth performance, innate immunity and disease resistance of olive flounder against Streptococcus iniae and to examine the efficacy of Bacillus spp. on water quality reducing ammonia concentration and increasing fish survival. In the first experiment, a basal diet was prepared and regarded as a control and three other diets were prepared by supplementing one of three Bacillus spp. (B. subtilis, B. pumilus or B. licheniformis) at the dietary level of 0.5%. Triplicate groups of fish (initial body weight, 25g) were fed one of the four diets for eight weeks. Fish fed with B. subtilis containing diet showed significantly higher growth performance and feed efficiency than fish fed with the control diet. Also, significantly higher survival rates were observed in fish fed B. subtilis or B. pumilus containing diets during the feeding trial. Phagocytic activity was significantly increased in fish fed the probiotic containing diets and higher superoxide dismutase activity was observed in fish fed B. pumilus or B. licheniformis when compared to the control. However, serum lysozyme and myeloperoxidase activities did not significantly differ compared to the control. After a challenge with S. iniae, fish fed B. subtilis or B. licheniformis showed significantly higher survival rates compared to fish fed the control diet. In the second experiment, fish (30.1g) were fed a commercial diet for three weeks and then they were distributed to nine tanks at a density of 30 fish per tank (3 replicates per treatment). Fish were fasted for 5days in static water system, while one of two probiotics, B. subtilis or B. licheniformis was treated every 24h into the rearing water at the concentration of 104 CFUml−1. During the trial, significantly decreased ammonia concentration and fish mortality were observed by the supplementation of B. subtilis into the rearing water. The results in these studies indicate that B. subtilis has beneficial effects on growth performance, innate immunity and disease resistance of olive flounder and quality of the rearing water. [Copyright &y& Elsevier]

The effects of Bacillus sp. supplementation of different types of cells, such as spores and vegetative cells, on fish growth performance, intestinal microbial diversity alteration and immunity in juvenile olive flounder (Paralichthys olivaceus) were investigated. The fish were divided into three groups and provided with either a basal diet (control), Bacillus sp. vegetative cell (VCS) or spore (SS) supplemented diet for 8 weeks. At the end of the experiment, significant differences (P <.05) were found in terms of weight gain, specific growth rate, feed conversion ratio and protein efficiency ratio between the VCS and control groups. Respiratory burst, superoxide dismutase activity, and lysozyme activity, which are innate immune indicators, were observed with positive alterations (P <.05) in SS compared to controls. Intestinal microbial diversity analysis showed that the SS group had an increased richness estimate (Chao 1, ACE, and Jackknife) compared with the control group. Diversity estimates (Shannon and reverse Simpson) revealed that the VCS group was increased compared with the control group. Analyzing the similarity between groups through beta-diversity, Venn diagram, and heatmap analysis, the control and VCS groups were similar, and the SS group was different. IL-1β and TNF-α expression levels in the liver and spleen were increased in the SS group compared with the control group. In growth-related gene expression analysis, only growth hormone increased in the VCS group compared with the control group. In an in vivo challenge experiment with Streptococcus iniae (1 × 108 CFU/mL), the survival rates of the VCS and SS groups were 14.29% and 28.57%, respectively, when the control mortality reached 100%. Therefore, we concluded that supplementation of Bacillus sp. with different physiological processes affects the growth performance and immune activity of flounder. In particular, VCS can induce growth performance and growth-related gene expression, and SS can alter nonspecific immune and immune-related gene expressions. • The effect of dietary supplementation is affected by the Bacillus physiological process. • Dietary Bacillus vegetative cell supplementation improves growth performance. • Bacillus spore supplementation affects the intestinal microbial composition. • Nonspecific immunity is altered by Bacillus spore supplementation. • Pro-inflammatory cytokines are upregulated by dietary spore supplementation. [ABSTRACT FROM AUTHOR]

The overall performance and well-being of juvenile olive flounder were evaluated in response to three isonitrogenous and isolipidic extruded feed pellets containing either wheat flour (WF), potato (PS) or corn starch (CS), as a dietary carbohydrate source. Following the 2-week acclimation period, triplicate groups of fish (16.6 ± 0.01 g) were assigned to each experimental diet and fed to apparent satiation for 8 weeks. The results of the extruded feed pellet's physical quality tests revealed that dietary inclusion of PS could significantly enhance the water stability of the extruded feed pellets. In addition, PS and CS diets had significantly higher bulk density than WF diet. Feeding juvenile flounders with these experimental diets, however, did not induce any significant changes in their overall performance. Significantly higher serum lysozyme activity was recorded in fish fed the PS and CS diets than those fed the WF diet. Fish fed the WF and CS diets had significantly higher superoxide dismutase activity than PS group. Expression of the immune-related genes, including SOD2, EPX-L, TNF-L, IL-6, and TIPRL, was notably up-regulated in liver of fish fed the PS and CS diets compared to those fed the WF diet. Interestingly, however, an inverse expression pattern was found for the same genes in the spleen where lower expression levels were detected in the PS and CS groups than the WF group. Overall, our findings revealed that while dietary utilization of PS produced an extruded feed pellet with markedly higher physical quality than either WF or CS, neither of these starch sources were able to significantly impact the flounder's performance. Further studies are needed to elucidate the potential long-term consequences of the invoked immune response in the PS and CS groups. • Overall performance and well-being of juvenile olive flounders were evaluated in response to the extruded feed pellets containing either wheat flour, potato starch or corn starch as dietary starch sources. • Diets containing potato starch showed significantly higher water stability than the other two experimental diets. • Dietary inclusion of either potato or corn starch in the extruded diet significantly affected immune-related genes expression in the liver and spleen of flounders. • The expression patterns of the target genes involved in the immune response were opposite in the liver and spleen after feeding with different starch sources. [ABSTRACT FROM AUTHOR]

Mercury (Hg) is known as a highly toxic heavy metal, and its toxicity varies depending on its form due to different toxicokinetics between inorganic and organic Hg. Limited information on comparison of Hg toxicity concerning its chemical form by oral exposure is currently available in cultured fishes. Therefore, we conducted a comparative study to have a better understanding of distinct toxic effects between mercuric chloride (HgCl 2) and methylmercury chloride (CH 3 HgCl) in Korean rockfish. The 12-weeks dietary exposure of HgCl 2 and CH 3 HgCl with its graded levels (0.4–6.4 ppm) (2 × 5 factorial design) in the young-of-the-year rockfish (initial weight: 82 ± 0.3 g) resulted in neither interactive nor main effects on whole-organism responses, including growth, feed utilization, and survival. However, the distinct pattern of Hg accumulation between the two forms in dorsal muscle, brain, liver and kidney tissues was observed, showing that the rockfish fed the CH 3 HgCl-contained diets exhibited the dose-dependent accumulation throughout the sampling points (1, 2, 4, 8, and 12 weeks post feeding), whereas those fed the HgCl 2 -contained diets did not show such response. The CH 3 HgCl exposure induced higher oxidative stress and immunotoxicity, reflected by the elevated plasma superoxide dismutase and lysozyme activities, respectively. In addition, the CH 3 HgCl-induced alteration in plasma measurements, including the plasma aspartate transaminase activity and total protein level was found. Taken together, the dietary exposure of methylmercury chloride had more pronounced toxic effects than mercuric chloride in the young-of-year rockfish, needed to be taken into consideration for regulation of maximum allowed levels for Hg by its chemical form. • Dietary-borne methylmercury chloride had higher toxicity than mercuric chloride. • Distinct toxicokinetics between the organic and inorganic mercury was found. • Immunotoxicity resulting from the methylmercury chloride exposure was detected. • Impaired liver function by the methylmercury chloride exposure was observed. [ABSTRACT FROM AUTHOR]

This study was carried out to investigate the effect of dietary differences on intestinal microbial population alteration and its relationship to immune-related gene expression in juvenile olive flounder (Paralichthys olivaceus). Initially, flounder were divided into three groups and supplemented with fishmeal diet (FM), fishmeal replaced by plant protein (termed low-fishmeal (LFM)), and Bacillus sp. SJ-10 probiotic-inoculated LFM (Pro) for 4 weeks. At the start (Initial group) and after completing the feeding trial, intestines were subjected to microbiota analysis and immune-related gene expression. The results of the intestinal microbiota analysis demonstrated that the FM and LFM groups' microbial richness (Chao1, ACE, and Jackknife) and diversity (Shannon and Simpson) did not differ significantly (P >.05) compared to the Initial group. However, the Pro group exhibited increased (P <.05) richness compared to all other groups, but its diversity was lower than that of the Initial group. A similar alteration phenomenon was also found in community composition between these two groups. At the phylum level, the most abundant phylum was Proteobacteria for all groups, but the second most abundant phylum in the Initial and Pro groups was Bacteroidetes, whereas in the FM and LFM groups, it was Firmicutes. An additional analysis of genus-level community composition and prediction of functional composition analysis showed differences among the groups. In the intestine, the transcription of interleukin (IL)-10 and IL-1β was increased more in the LFM and Pro groups compared to the FM group. IL-6 was increased only in the Pro group, and tumor necrosis factor-α (TNF-α) gene expression did not differ significantly among the groups. Therefore, we concluded that dietary changes affect intestinal microbiota composition and immune-related gene expression; in particular, diets containing probiotics can lead to greater change during the same feeding period. • Dietary changes affect intestinal microbiota composition and immune-related gene expression of olive flounder. • Probiotic have a greater impact on intestinal microbial diversity and composition than changes in fishmeal content. • Feed composition changes and probiotic supplements can manipulate the intestinal microbiota of olive flounder. [ABSTRACT FROM AUTHOR]